BIOLOGY AND MANAGEMENT OF COMMON GROUNDSEL (Senecio vulgaris L.) IN STRAWBERRY
DISSERTATION
Presented in Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy in the Graduate School of The Ohio State University
By
Rodrigo Figueroa, B.S., Agronomist *****
The Ohio State University 2003
Dissertation Committee: Professor Douglas Doohan, adviser Approved by: Professor John Cardina, co-adviser Professor Kent Harrison ______Professor Daniel Herms Adviser Horticulture and Crop Science Graduate program
ABSTRACT
Common groundsel (Senecio vulgaris L.) is an annual weed of Mediterranean origin that has become a worldwide pest in many crop production systems, including small fruit crops like strawberry. Management of common groundsel has been difficult because of its tolerance of many control measures and resistance to some herbicides, and because of inadequate or conflicting information about its biology. Studies were conducted in Ohio to determine the effect of common groundsel’s maternal environment on seed dormancy, describe the pattern of seedling emergence and seed persistence, and to evaluate the response of common groundsel and strawberry to herbicides. Experiments were conducted using local seeds and seeds collected along a 700-km transect from
Michigan to Kentucky. Freshly matured seeds collected from sites along this transect differed in germination response to temperature, but when plants from these sites were grown in a common environment the seeds responded uniformly to temperature. In growth chamber studies, seeds maturing on plants growing in cold short day conditions were mostly dormant whereas seeds produced on plants in warm long day conditions were mostly non-dormant. Changing temperature conditions from warm to cold increased seed dormancy, especially when the change occurred in early reproductive stages. The dormancy status of buried seeds varied throughout the year, mostly in response to soil temperature. Seedling emergence was limited by both rainfall and temperature but there was an interaction with tillage. A logistic regression model demonstrated that in tilled ii soil, emergence was stimulated by small amounts of rainfall, but in no-till conditions about ten-times as much rainfall is required to stimulate emergence. Nearly all buried seeds germinated or died during two years of burial in soil. In newly established strawberries, common groundsel was controlled with the herbicide sulfentrazone (N-[2,4- dichloro-5-[4-(difluoromethyl)-4,5-dihydro-3-methyl-5-oxo-1H-1,2,4-triazol-1-yl-
]phenyl]methanesulfonamide) applied before seedling emergence at rates of 0.15 and 0.3 kg/ha. Stunting was observed in strawberry plants as herbicide rates increased, and was more severe on a high pH (> 6.5) soil and on cultivar ‘Allstar’ compared with ‘Jewel’.
Late summer applications of clopyralid (3,6-dichloro-2-pyridinecarboxylic acid) herbicide (0.1-0.2 kg/ha) controlled common groundsel without suppressing strawberry foliage or reducing yield.
iii Dedicated to my wife Andrea for her love, companionship, support, patience, and faith throughout these years. To Jose Tomas and Rosarito for many smiles that cheered
me up and gave me strength.
iv ACKNOWLEDGMENTS
I want to thank God for giving me the opportunity to study at OSU and learn from all the incredible people he has put in our way. Thanks to my parents and all my family, for all the support that made us through many difficulties.
I would also like to express my special gratitude to the following individuals and institutions: to my adviser, Dr. Douglas Doohan for his guidance, support, patience and friendship but most importantly for making my PhD studies both a challenging and growing experience. To my co-adviser, Dr. John Cardina for being a model researcher and friend. To my dissertation committee members, Drs. Daniel Herms and Kent
Harrison for their valuable suggestions and guidance with the plant material collections, as well as with the manuscripts review. To the Pontifical Catholic University of Chile,
School of Agriculture and Forestry, for financial support during these four years. To Dr.
Marcelo Kogan, my undergraduate advisor and friend, who introduced me to weed science and pushed me to aspire to the PhD. To Dr. Joel Felix for his positive criticism aimed to improve my work. To Tim Koch for helping during the herbicide applications and evaluations. To Cathy Herms for her many hours of extra work, patience and support finishing my dissertation. To Paul McMillen for his prompt responses to field operations needs and great humor. To John Elliott for his help with strawberry field management, especially during many night hours of frost protection. To all OARDC personal, v particularly to Bert Bishop for his help with questions of statistical analysis. To graduate students in the weed science program, Karen Amisi, Mark Frey and Lynn Sosnoskie. To all summer helpers in the weed lab that spent many hours of hard work: Hayley Bennett,
Ben Doohan, Noah Myers, Mike Peters, Josh Reinford, and Elizabeth Zaleski.
Finally, many thanks to our friends for life: Kitty and Pablo Valencia, Cheryll and
Ted Radovich, and David Scurlock. You have all made these years an incredible and enriching experience.
vi VITA
February 22, 1968……………….. Born – Santiago, Chile 1991……………………………… BS, Pontifical Catholic University of Chile (PUC). 1993……………………………… Agronomist, PUC. 1993 to present…………………… Assistant Professor, PUC 1999 –2003………………………. Graduate Research Associate, The Ohio State University, USA.
PUBLICATIONS Robinson, D.E., O’Donovan, J.T., Sharma, M.P., Doohan, D.J. and R. Figueroa. 2003. The biology of Canadian weeds. 123. Senecio vulgaris L. Canadian Journal of Plant Science, 83 (3): 629-644. Figueroa, R., Doohan, D. and J. Cardina. 2002. Efficacy and crop tolerance of sulfentrazone on strawberries. NCWSS Abstracts 57. Figueroa, R. and D.J. Doohan. 2002. Germination response of six common groundsel (Senecio vulgaris L.) weed collections to temperature and burial. WSSA Abstracts 42: 82-83 Kogan, M., Figueroa, R. and Gilabert, H. 2002. Weed control intensity effects on young radiate pine growth. Crop Protection, 21 (3): 253-257. Kogan, M. and R. Figueroa. 2002. Carry over of flazasulfuron applied post transplanting of tomato. Ciencia e Investigación Agraria, 29 (3): 137-143. Figueroa, R. 1993. Tolerance of Eucalyptus globulus young seedling plants to soil active herbicides. Pontifical Catholic University of Chile. Thesis.
FIELDS OF STUDY Major field: Horticulture and Crop Science vii TABLE OF CONTENTS
Abstract...... ii
Dedication...... iv
Acknowledgments...... v
Vita...... vii
List of Tables ...... x
List of Figures...... xii
Chapters:
1. Introduction...... 1
Literature Cited...... 5
2. Maternal environments effects on seed dormancy of common groundsel ...... 7
Abstract...... 7
Introduction...... 10
Materials and Methods...... 12
Results and Discussion ...... 17
Literature Cited...... 31
3. Common groundsel seed longevity and seedling emergence ...... 35
Abstract...... 35
Introduction...... 37
viii Materials and Methods...... 40
Results and Discussion ...... 46
Literature Cited...... 58
4 Management of common groundsel in newly established strawberry...... 62
Abstract...... 62
Introduction...... 64
Materials and Methods...... 66
Results and Discussion ...... 72
Literature Cited...... 83
5 Response of established strawberry to preemergence and postemergence
herbicides ...... 86
Abstract...... 86
Introduction...... 87
Materials and Methods...... 89
Results and Discussion ...... 91
Literature Cited...... 96
6 Summary and conclusions ...... 98
Bibliography ...... 103
Appendices
A Growth response of annual weed species to sulfentrazone dose ...... 115
ix LIST OF TABLES
Table
2.1 Monthly air temperatures (C) for 2000 and 2002 at different collection sites of common groundsel. Only collection sites with nearby weather stations are presented. Source: NOAA, 2003. National Climatic Data Center (www.ncdc.noaa.gov) ...... 21
2.2 Plant height, biomass, and inflorescence response of common groundsel to different growing conditions 42 days after sowing. Temperature settings were 15/8 or 22/15 C with an 8 h warm cycle. Photoperiods were 8/16 or 16/8-h light/dark. Light was 8-h core irradiance at 400 (±25) µmol m-2 s-1 PPFD. Photoperiod was extended in growth chambers set with a 16/8-h light/dark period by two 120-W incandescent bulbs that provided approximately 35(±5) µmol m-2 s-1 PPFD...... 25
3.1 Parameters for common groundsel emergence equations and rainfall needed for 50 % probability of emergence of two soil disturbance levels. Equations for probability were calculated using the logistic model: log [p/(1-p)]= α + τi + β * Rainfall; where p = probability of emergence; α = intercept; τi = temperature; β = rainfall coefficient; and Rainfall= cumulative weekly rainfall...... 54
4.1 Strawberry injury and common groundsel control 3 weeks after application (WAA) in response to herbicides applied the day of transplanting in 2000. Foliar injury index: 0= no damage; 1= leaf chlorosis <50%; 2= leaf chlorosis >50% and petioles twisting; 3= leaf chlorosis >50% and slight leaf necrosis restricted to the margin; 4= severe leaf necrosis, and 5= plant death...... 78
4.2 Response of newly planted strawberry at 1 and 3 weeks after application (WAA) to herbicides applied immediately after transplanting. Combined for 2001 and 2002. * P= 0.1 was used to reduce risk of type II error and to make analysis more sensitive to potential damage ...... 79
x 4.3 The response of Allstar and Jewel strawberry cultivars to sulfentrazone rates and soil pH levels at 3 and 6 weeks after application (WAA) in 2002. NS= no significantly different; * = p ≤ 0.05; ** = p ≤ 0.01; *** = p ≤ 0.0001...... 80
5.1 Strawberry foliage growth at 3 and 6 weeks after treatment (WAT) and yield response to clopyralid Data were combined for 2001and 2002 after ANOVA indicated no year effect or interaction between years with the herbicide treatments. Values for treatments within columns followed by the same letter are not significantly different according to Fisher’s protected LSD test (P≤ 0.1) ...... 94
xi LIST OF FIGURES
Figure
2.1 Whole (top) and dissected (bottom) inflorescence stages of common groundsel. From right to left: a) Bud; b) Anthesis; and c) Fruit set...... 16
2.2 Cumulative germination of common groundsel seeds in response to constant incubation temperature for 15 days. Seeds were from plants collected from six locations (top) and from progeny of those plants grown in a common environment (bottom)...... 20
2.3 Germination response of common groundsel under six constant temperatures for 2 weeks. Seeds were collected in June 2002 from four different locations in the Midwest (combined data for July and August 2002 replications)...... 22
2.4 Germination response of four types of common groundsel seeds to six constant temperature points. Seeds were from mother plants grown in four different environments, all with 8 h of warm cycle: 22/15 C and 16 h daylength (WLD); 22/15 C and 8 h daylength (WSD); 15/8 C and 16 h daylength (CLD); and 15/8 and 8 h daylength (CSD). Light was 8-h core irradiance at 400(±25) µmol m-2 s-1 PPFD. Photoperiod was supplemented in both cool and warm long daylength environments by two 120-W incandescent bulbs that provided approximately 35(±5) µmol m-2 s-1 PPFD. (Michigan and Kentucky, pooled data)...... 26
2.5 Germination of common groundsel seeds originating from plants collected at Essexville (MI) and Lexington (KY) and later grown in constant and non-constant thermal environments. WW= plants grown continually at 22/15 C; CC= plants grown continually at 15/8 C; WC=plants grown at 22/15 C and transferred to 15/8 C at the designated growth stage until seed maturation; CW=plants grown at 15/8 and transferred to 22/15 C at the designated growth stage until seed maturation ...... 28
3.1 Germination of common groundsel seeds after burial in the field and incubation at 20/10 C and 14 h of white fluorescent light...... 48
xii 3.2 Cumulative emergence of common groundsel in response to soil disturbance at Kingsville, Ohio during 2002. Frequent soil disturbance plots ( ) were raked every other week. Infrequent soil disturbance plots ( ) were cultivated only twice each year (April and September) ...... 51
3.3 Cumulative emergence of common groundsel in response to soil disturbance at Kingsville, Ohio during 2003. Frequent soil disturbance plots ( ) were raked every other week. Infrequent soil disturbance plots ( ) were cultivated only twice each year (April and September) ...... 52
3.4 Percent cumulative emergence of common groundsel from an artificially seeded seedbank in August 2001 and 2002.Seedlings were removed after counting. Data presented has been combined across years and two locations (Columbus and Wooster, Ohio)...... 57
4.1 Control of common groundsel in 2001 and 2002 at 18 WAA of herbicide treatments to newly transplanted strawberry plants. Error bar represent the LSD (P = 0.05) to compare treatment response combined by years...... 81
4.2 The effect of common groundsel growth stage and rate of sulfentrazone on common groundsel height 3 weeks after application (WAA). Nonlinear regression (solid symbols) and raw means (outline symbols) were plotted with means combined over experiments for plant height at 3 WAA as a percentage of the untreated control. Stages of common groundsel growth were: preemergence (PRE), cotyledon (COT) = seedlings at the cotyledon stage, early post (EPOST) = seedlings at the 4 leaf stage and late post (LPOST) = seedlings at the 10 leaf stage ...... 82
5.1 Control of common groundsel with clopyralid applied postemergence to ‘Jewel’ strawberry (2001 and 2002). Regressions were combined over years. Y axis is common groundsel control, as % of growth (height) of the untreated control, at 3 and 6 weeks after treatment (WAT) and flowering at 6 WAT...... 95
A.1 Response (plant height) of four stages of common chickweed (Stellaria media (L.) Vill) growth to sulfentrazone. Nonlinear regression (full symbols) and raw means (empty symbols) are plotted with means combined over experiments for plant height at 21 d after treatment as a percentage of the untreated control. Stages of growth were: preemergence (PRE), cotyledon (COT) with seedlings at the cotyledon stage, early post (EPOST) with seedlings at the 4 fully expanded leaf stage and late post (LPOST) with seedlings at the 10 leaf stage...... 116
xiii A.2 Response (plant height) of four stages of common lambsquarter (Chenopodium album L.) growth to sulfentrazone. Nonlinear regression (full symbols) and raw means (empty symbols) are plotted with means combined over experiments for plant height at 21 d after treatment as a percentage of the untreated control. Stages of growth were: preemergence (PRE), cotyledon (COT) with seedlings at the cotyledon stage, early post (EPOST) with seedlings at the 4 fully expanded leaf stage and late post (LPOST) with seedlings at the 10 leaf stage...... 117
A.3 Response (plant height) of four stages of common mallow (Malva neglecta Wallr.) growth to sulfentrazone. Nonlinear regression (full symbols) and raw means (empty symbols) are plotted with means combined over experiments for plant height at 21 d after treatment as a percentage of the untreated control. Stages of growth were: preemergence (PRE), cotyledon (COT) with seedlings at the cotyledon stage, early post (EPOST) with seedlings at the 4 fully expanded leaf stage and late post (LPOST) with seedlings at the 10 leaf stage...... 118
A.4 Response (plant height) of four stages of redroot pigweed (Amaranthus retroflexus L.) growth to sulfentrazone. Nonlinear regression (full symbols) and raw means (empty symbols) are plotted with means combined over experiments for plant height at 21 d after treatment as a percentage of the untreated control. Stages of growth were: preemergence (PRE), cotyledon (COT) with seedlings at the cotyledon stage, early post (EPOST) with seedlings at the 4 fully expanded leaf stage and late post (LPOST) with seedlings at the 10 leaf stage...... 119
A.5 Response (plant height) of four stages of common purslane (Portulaca oleraceae L.) growth to sulfentrazone. Nonlinear regression (full symbols) and raw means (empty symbols) are plotted with means combined over experiments for plant height at 21 d after treatment as a percentage of the untreated control. Stages of growth were: preemergence (PRE), cotyledon (COT) with seedlings at the cotyledon stage, early post (EPOST) with seedlings at the 4 fully expanded leaf stage and late post (LPOST) with seedlings at the 10 leaf stage...... 120
A.6 Response (plant height) of four stages of yellow woodsorrel (Oxalis stricta L.) growth to sulfentrazone. Nonlinear regression (full symbols) and raw means (empty symbols) are plotted with means combined over experiments for plant height at 21 d after treatment as a percentage of the untreated control. Stages of growth were: preemergence (PRE), cotyledon (COT) with seedlings at the cotyledon stage, early post (EPOST) with seedlings at the 4 fully expanded leaf stage and late post (LPOST) with seedlings at the 10 leaf stage...... 121 xiv CHAPTER 1
INTRODUCTION
During the last two decades, weed science as well as other plant protection areas has struggled to respond to a growing ecological public concern. There is a continuing need for more knowledge on how to control weeds and their impact on crop production, but there is also a need to reduce the use of herbicides. This important requirement will only be achieved if more and better understanding of weed biology is developed. The present research was proposed to specifically generate new information related to the biology and ecology of common groundsel (Senecio vulgaris), and the implications for control in strawberry crops.
A member of the Asteracea family, the genus Senecio is one of the largest in the plant kingdom, containing over 2,000 species, although only a few species are common weeds. Other weedy species in the genus include tansy ragwort (Senecio jacobea L.), woodland groundsel (Senecio sylvaticus L.) and cressleaf groundsel (Senecio glabellus
Poir.). In the U.S., other common names for groundsel include grinsel, simson, birdseed and chickenweed (Britton and Brown 1898; Georgia 1942)
1 Common groundsel is present in many crops, including orchards, forages, cereals, mint, berries, and row crops, as well as in ornamentals and vegetable gardens (Aldrich-
Markham 1994). It is specially a problem in forage crops because it contains toxic alkaloids which can cause serious and incurable liver disease in cattle and horses (Senesac 1991).
Common groundsel (Senecio vulgaris L.) appears as a weed in many crops and countries. It behaves as a weed from Mongolia and Iceland in the north to New Zealand in the south. In general, the reports of major problem with this weed are from Europe and
North America, but there are some important exceptions. Holm et al. (1997), in their classic account reported that common groundsel was a serious weed of maize in Canada, of woody plant nurseries in England, Norway, and Sweden; and of horticultural crops such as vegetables and small fruits in the Netherlands, Norway, Sweden, and Scotland. It is a principal weed of most irrigated crops in Mongolia, of legumes in Hungary, of maize in
England, of woody plant nurseries in the United States, of vineyards in Hungary and Italy, of wheat in Hungary and Korea, and of many vegetable crops, small fruits, and some orchards in Belgium, Canada, England, Germany, Hungary, Ireland, New Zealand, Spain,
Turkey and the United States. In a recent survey, common groundsel was found to be one of the worst weeds of vineyards and soft fruits, especially strawberries, in European countries
(Clay 1987). In an extensive weed survey across Canada, Groh and Frankton (1949) reported that groundsel was generally distributed over the country but was of low frequency in most fields.
Research has also demonstrated the competitive ability of groundsel in horticultural and agronomic crops. In California, United States, only 3 to 8 groundsel plants/m2 reduced
2 yields of broccoli by about 25 % (Agamalian 1983). In a similar way, (Norris 1981) reported that groundsel reduced the yield of seedling alfalfa by 50% at first cutting. Common groundsel is such a pervasive and enduring inhabitant of the world’s agriculture that it seems to find a strategy for being a continued nuisance even in the face of considerable change in field management.
Cussans (1966) in England reported a general decrease in density of annual dicotyledonous weeds with the beginning of direct drilling and minimum soil disturbance.
Nielsen and Pinnerup (1982) in Sweden made twice-yearly weed counts in spring barley grown with reduced tillage and found that common groundsel was one of the weeds that could increase in such a system. As new black peat soils were opened to agriculture in
Ireland, groundsel, with the seeds probably blown in by the wind, increased quickly during the nutrient-rich early cultivation stages but tended to diminish in numbers thereafter. Rola
(1979) reported on a 10-year study on the weed flora of degraded black soils in Poland, where a combination of suitable cropping and use of herbicides caused the disappearance of seven species including common groundsel.
In North America, common groundsel is found from Newfoundland and Hudson
Bay to Virginia and North Carolina, west to Minnesota, South Dakota and Michigan. It also is found on the Pacific Coast (Britton and Brown 1898). Common groundsel was the first weed species in the United States discovered to have biotypes resistant to triazine (simazine, atrazine) herbicides. Since the initial discovery of a resistant biotype in a field nursery in western Washington thirty-four years ago, several hundred thousand acres have become
3 infested in the Pacific Northwest. Infested nursery plant material was shipped to other parts of the country and thought to be responsible for some movement of this biotype.
Common groundsel is arguably the most serious weed problem faced by some
Ohio strawberry growers and nurserymen. This species "escapes" most control practices and seems to be getting worse. It is also an "international/cosmopolitan" weed problem of the U.S. and Chile, my home country.
This dissertation consists of four studies described in the following chapters written as manuscripts to be submitted to journals of the Weed Science Society of
America. The first study deals with effects of maternal environments on common groundsel seed dormancy. The objectives of this study were to: 1) characterize the germination response to incubation temperature in seeds of common groundsel from populations collected along a 700 km N-S transect in the Midwest, 2) characterize effects of maternal temperature and day-length conditions on seed germination of common groundsel populations, and 3) determine the reproductive development stage at which an environmental signal alters the germination behavior in mature seeds.
The second study was conducted to describe common groundsel seed longevity and seedling emergence. The objectives of this study were to determine the dormancy status of common groundsel seeds over 24 months, and to describe the effect of tillage and fertilizer on the pattern of seedling emergence and the rate of depletion of seeds from the soil seed bank.
The third study was conducted to address the management of common groundsel in newly established strawberry. This research was conducted to confirm selectivity of
4 several newly developed herbicides on strawberry and their efficacy on common groundsel in order to integrate the most promising product(s) into strawberry weed management recommendations.
The fourth study addressed the response of established strawberry to postemergence herbicides. The objective of this research was to confirm clopyralid efficacy on common groundsel, tolerance of established strawberries to the herbicide, and to provide data to support development of recommendations.
LITERATURE CITED
Agamalian, H. S. 1983. Competition of annual weeds in broccoli. Proceedings of the Western Society of Weed Science 36: 192.
Aldrich-Markham, S. 1994. Common groundsel: Senecio vulgaris L. PNW. Corvallis, Or. : Washington, Oregon, and Idaho State Universities, Cooperative Extension Service.
Britton, N. L. and A. Brown. 1898. An illustrated flora of the Northen United States, Canada and the British possesions. New York, Charles Scribner's Sons
Clay, D. V. 1987. The response of simazine-resistant and susceptible biotypes of Chamomilla suaveolens, Epilobium ciliatumand Senecio vulgaris to other herbicides. Proceedings of the 1987 British Crop Protection Conference-Weeds.
Cussans, G. 1966. The weed problem. 8th Brit. Weed Control conference.
Georgia, A. 1942. Manual of weeds. New York, The Mcmillan Co.
Groh, H. and C. Frankton. 1949. Canadian weed survey. Ottawa., Dominion of Canada. Department of Agriculture. 5
Holm, L., J. Doll, E. Holm, J. Pancho and J. Herberger 1997. World weeds: natural- histories and distribution. New York, John Wiley & Sons, Inc.: 740-750.
Nielsen, H. and S. Pinnerup. 1982. Reduced cultivation and weeds. 23rd Swedish Weed Conference.
Norris, R. 1981. Weed competition in seedling alfalfa. 31st Weed Science Society of America Conference.
Rola, J. 1979. The combined effect of crop plants and herbicides on the weed population. European Weed Research Society Symposium., Mainz, Germany.
Ryan, G. F. 1970. Resistance of common groundsel to simazine and atrazine. Weed Science 18(5): 614-616.
Senesac, A. 1991. Common groundsel Senecio vulgaris L. Long Island Hortic News. Riverhead, N.Y. : Cornell Cooperative Extension.
6 CHAPTER 2
MATERNAL ENVIRONMENT EFFECTS ON
COMMON GROUNDSEL SEED DORMANCY
ABSTRACT
Common groundsel has become a serious problem weed due to its adaptability to environments and selection pressures. However, there are confusing reports regarding the germination conditions favored by this species and whether it behaves as a winter or summer annual. Research was conducted to characterize the germination response to temperature in common groundsel seeds from populations collected along a 700 km N-S transect (Lexington, KY to Essexville, MI), to determine how maternal temperature and day-length conditions affect germination, and to describe the relationship between maternal environmental conditions and the germination behavior of mature seeds.
Common groundsel seeds were collected in late May 2000 and June 2002 from 35 and
400 randomly selected plants, respectively at each site. Germination response to temperature was first evaluated 2 weeks after collection and repeated monthly 3 times during the summer of 2000; a follow up experiment was conducted during the winter of
2001. To reduce maternal effects and prevent crossing, plants from each location were
7 grown under identical conditions in separate greenhouse rooms with a 14/10-h thermoperiod of 22/18 C. To evaluate effects of maternal environments, seed germination was tested on plants grown in growth chambers with warm long days (WLD:
22/15 C and 16 h of light), warm short days (WLD: 22/15 C and 8 h of light), cold long days (CLD: 15/8 C and 16 h of light), and cold short days (CSD: 15/8 C and 8 h of light).
There was a broad optimum temperature range (10-15 C) for germination, which was similar among sites. Two germination patterns were observed: 1) Seeds from the southern locations averaged 80 – 90% germination across the range of 5 – 25 C; 2) Seeds from northern locations had reduced germination as incubation temperatures move away from about 15 C. High percent germination at 5 C observed in seeds from southern locations may represent adaptation to late fall germination and successful growth and reproduction during winter months. Reduced germination at 5 C observed in seeds from northern locations would minimize losses to the seed bank due to over-winter mortality of late fall- germinated seedlings. However, when plants from the different locations were grown in a common environment, seeds collected had a germination response that was similar across the temperature gradient. Seeds from the WSD and WLD environments germinated at a high percentage (80 %) across the range from 5-25 C indicating that these conditions had produced non-dormant seeds. In contrast, 20% or fewer of the seeds from plants in the
CLD and CSD chambers germinated regardless of temperature, suggesting that dormancy had been induced by the cool maternal environment. Results suggested that under summer conditions, common groundsel produced tall plants with relatively few inflorescences yielding non-dormant seeds, whereas under fall conditions the plants were
8 short, inflorescences were abundant, and seeds were highly dormant. Changing temperature conditions from warm to cold increased seed dormancy, especially when cold temperatures were imposed in early reproductive stages. The temperature adaptations, often interacting with day-length, allow common groundsel to modify its reproductive strategy in response to environmental conditions. Results suggest that different management approaches might need to be employed for common groundsel plants maturing in summer compared with those maturing in autumn.
9 INTRODUCTION
Dormancy of weed seeds varies in degree between and within populations. In many species seed dormancy also varies within an individual parent plant, resulting in variable germination responses to different environmental conditions (Gutterman 1992).
Environmental factors known to modify seed germination within a population include: day length (Gutterman 1973; Gutterman 1978); temperature (Junttila 1973; Heide et al.
1976); parental photothermal environment (Kigel et al. 1977); light quality (Gutterman and Evenari 1972) and altitude (Dorne 1981). Some variation may be of genetic origin, but much is caused by the environmental conditions under which the seeds matured (i.e. the maternal environment), including position of the seed on the parent plant and abiotic conditions of temperature, day length, water availability, etc. The effects of environmental factors on seed maturation have been summarized by Fenner (1991),
Gutterman (2000), Baskin and Baskin (1998) and Tollenaar (1999).
The temperature environment of parent plants can influence seed germination of many species. Using vegetatively propagated mother plants of common lilac (Syringa vulgaris), Junttila (1973) observed that seeds from mother plants grown at 18-24 C were partially dormant, while seeds from plants grown at 12 C were not dormant at all.
Dormancy of lettuce (Lactuca sativa) seeds decreased with an increase in mean temperatures 10 or 30 days prior to seed harvest (Harrington and Thompson, 1952).
Seeds of wheat (Triticum aestivum) produced in dry, warm years were less dormant than those produced in cool, wet summers (Belderok, 1961). Likewise, dormancy decreased in seeds of rose (Rosa spp.) with an increase in mean temperatures 30 days prior to 10 harvesting (VonAbrams and Hand, 1956). Other examples of the effect of parental thermal environment on seed germination can be found in Gutterman (2000).
Common groundsel is a cosmopolitan weed of horticultural and agronomic crops
(Holm et al. 1997) and has recently become a serious problem in vegetable, small fruit, and ornamental nursery plants in Ohio. Common groundsel has shown a high degree of adaptability under different environments and selection pressures. Common groundsel tolerates many herbicides (Senesac 1991) and resistant biotypes have been reported for triazine (Ryan 1970) and nitrile herbicides (Mallony-Smith 1998). An interesting environmental adaptation of common groundsel is its strong light requirement for germination (Popay and Roberts 1970a,b). Common groundsel seeds had a strong requirement for white or red light to attain maximum germination at 20 C (Hilton 1983), although 35% germination was reported in the dark at 10 C (Popay and Roberts 1970a).
Biological factors that influence the success of common groundsel as a weed are summarized in Robinson et al. (2003). Research conducted in Europe predominates in their review, and there remains some confusion about the germination conditions favored by this species. For example, Roberts (1964) described a continuous pattern of germination and emergence in field experiments in England, which is contrary to observations in Ohio, USA. In some areas common groundsel is considered a winter annual and in other areas it is primarily a spring or summer annual (Robinson et al.,
2003). We have previously reported patterns of groundsel germination in OH and longevity of buried seed from populations collected in MI, OH and KY (Figueroa and
Doohan 2002). Variability in patterns of seed germination and adaptation in response to
11 environmental conditions experienced by the species in the Midwest US have not been described. Development of effective weed management recommendations for regional growers is limited by the inadequacy of the current knowledge of common groundsel germination in response to the environment.
The objectives of the research reported herein were: 1) characterize the germination response to incubation temperature in seeds of common groundsel from populations collected along a 700 km N-S transect in the Midwest, 2) characterize effects of maternal temperature and day-length conditions on seed germination of common groundsel populations, and 3) determine the reproductive development stage at which an environmental signal alters the germination behavior in mature seeds.
MATERIALS AND METHODS
Plant material collections
Common groundsel seeds were collected from sites along a 700 km transect between Lexington, KY and Essexville, MI in May 2000. Seeds were collected from 35-
45 plants, selected at random, within a 1 ha area at Bay Landscaping Inc, Essexville, MI;
Hillenmeyer Nurseries, Lexington, KY; Manbeck Nursery, New Knoxville, OH; Scarff’s
Nursery, New Carlisle, OH; North Branch Nursery, Pemberville, OH and Maurer Farm,
Wooster, OH. Seeds were cleaned by rubbing them through sieves with openings of
2380, 1000, and 500 microns, thereby removing all flower structures. Bulked seeds were stored separately by collection at room temperature of 20 ± 5 C in the laboratory at the
Ohio Agricultural Research and Development Center (OARDC, Wooster, OH).
12
Germination in common groundsel populations
The optimum temperature for germination of each collection was determined on a thermo-gradient table (TGT) equipped with cooling and heating water baths at opposite ends. Temperatures on the TGT were monitored with copper/constantan thermocouples connected to a Campbell® data logger. Seeds (50) were placed in Petri dishes and then imbibed in distilled water in an incubator at 4 C for 12 h in darkness then transferred to the TGT and exposed to constant temperatures of 5, 10, 15, 20, and 25 C for two weeks.
Treatments were combinations of common groundsel collection sites and temperatures.
They were replicated four times and germination was assessed every other day for 14 days. The first trial was started 2 weeks after seed collection and was repeated monthly three times during the summer of 2000.
During the winter of 2001, plants of each collection were grown in separate rooms of a greenhouse. Each room had a 14/10 h thermoperiod of 22/18 C. Natural daylight was supplemented and extended by high intensity sodium lamps. Seeds of each collection were harvested and stored as previously described and germination was tested on the
TGT following the identical protocol described above.
Effect of maternal temperature and day-length on germination
In June 2002 common groundsel seeds were collected from plants at the two sites that gave the most extreme difference in germination of seeds collected in 2000,
Essexville, MI and Lexington, KY. Seeds were collected from 400 plants (± 20) per
13 location. Seeds were cleaned, stored and germination was tested on the TGT as previously described. Germination was initially tested 2 weeks after seed collection and repeated in July and August 2002. Simultaneously, seeds from each site were sown in twenty 10-cm pots that were placed in a Conviron® BDR16 growth chamber with a 16/8 h photoperiod and a temperature regime of 25/15 C. Irradiance in the growth chamber was 400 (±25) µmol m-2 s-1 PPFD. At emergence seedlings were thinned to four per pot.
Ten days after seeding (DAS), seedlings were thinned to one per pot and moved into four different growth chambers with specific daylength and temperature environments.
Temperature settings were 15/8 or 22/15 C with an 8 h warm cycle. Photoperiods were
8/16 or 16/8-h light/dark. Light was 8-h core irradiance at 400 (±25) µmol m-2 s-1 PPFD.
Photoperiod was extended in growth chambers set with a 16/8-h light/dark period by two
120-W incandescent bulbs that provided approximately 35(±5) µmol m-2 s-1 PPFD. This level of irradiance was high enough to induce the photoperiod response but not sufficient to have an impact on photosynthesis. This design eliminated the potential confounding effect of differing high light-mediated growth rates on phenology (Tollenaar 1999;
Swanton et al. 2000). Data were collected on plant height, dry weight and number of total flowers per plant at final harvest. After maturation, seeds were collected and evaluated for germination on the TGT as previously described, with an additional temperature of 30
C.
14 Detection of growth stage sensitive to thermal environment
Forty potted common groundsel seedlings per collection site were grown in cool
(15/8 C) and warm (22/15 C) growth chambers with 14/10 h photoperiods and irradiance of 400 (±25) µmol m-2 s-1 PPFD. Six WAS, 20 plants per collection site from the warm chamber were moved to the cool GCH. Eight WAS, 20 plants from the cool GCH were moved to the warm. Before moving, three stages of inflorescence development were identified on each plant: a) Bud; b) Anthesis; and c) Fruit set (Figure 2.1). At the bud stage, sepals enclosed the inflorescence completely and anthers were not visible. During anthesis anthers projected over other floral structures and pollen was being released. At fruit set, anthers were no longer visible and the base of the inflorescence was swollen; seed color at this stage was brown. Three inflorescences in each stage on different clusters were tagged with plastic labels. When seeds matured, they were collected separately from each stage and germination was evaluated in an incubator at alternating temperatures of 20 and 10 C, (14/8 h thermoperiod). White fluorescent light (25 ± 5 µmol m-2 s-1) was supplied continuously.
Data were subjected to ANOVA using SAS GLM procedure (SAS 2000), combining data by repetitions after checking that no interactions existed. Percentage data were arcsine square root transformed to maintain homogeneity of variance. Only back- transformed data are presented. Means were separated with Fisher’s protected LSD at P=
0.05 (Steel et al. 1997). Non-transformed data were used for the plant height, dry weight, and flower number measurements.
15
c. b. a.
Figure 2.1: Whole (top) and dissected (bottom) inflorescence stages of common groundsel. From right to left: a) Bud; b) Anthesis; and c) Fruit set.
16 RESULTS AND DISCUSSION Germination in common groundsel populations
Germination response to incubation temperature varied in the seeds collected from different sites (Figure 2.2, top). The optimum temperature for germination of seeds from all sites was between 10 and 15 C. Germination ranged from 87-99% at 10 C and from 77-
99% at 15 C. At these incubation temperatures, 97-99% of the seeds from New Carlisle,
Wooster and New Knoxville, OH germinated. At 10 C germination of seeds from MI, KY, and Pemberville, OH ranged from 87-91%, whereas at 15 C the range of germination was from 77-96%. Two patterns were apparent in percent germination of seeds incubated at higher or lower temperatures. At 5 C, germination was relatively high (79-87%) in seeds collected from KY and from New Carlisle and New Knoxville OH, sites along the southern half of the transect. Germination of seeds from Wooster was greatly reduced (16%) at 5 C and seeds from Pemberville, OH and from MI had intermediate responses of 50 and 66% respectively. As at 5 C, the greatest germination at 20 and 25 C was observed in seeds from
New Knoxville and New Carlisle, OH and from KY, ranging from 89-94% at 20 C and from
80-94% at 25 C. Seeds collected at Wooster responded similarly at 20 C, whereas seeds from MI and Pemberville, OH had significantly reduced germination (77 and 62%, respectively). At 25 C, germination of seeds from MI (47%), Pemberville, OH (45%), and
Wooster, OH (29%) was significantly less than that of seeds collected elsewhere.
These data suggest that variability in germination of common groundsel corresponds to changes in latitude and climate. However, different results were obtained when seeds from plants of each collection site were grown in a common environment (Fig. 2.2, bottom).
17 Germination was similar for seeds from each collection site across the temperature gradient
(P value for sites ranged from 0.45-0.70 across the gradient). Germination at 10 and 15 C remained very high, nearly 100%, and this response was also observed at 20 C. Percent germination of seeds from each collection site declined somewhat at 5 C, ranging from 60-
80%. A trend towards reduced germination (80%) was noted in seeds of plants collected at
New Carlisle and KY when they were incubated at 25 C; however, this was not significant.
The initial experiment indicated that the germination response to temperature varied among plants from different environments and might be genetically controlled. The second experiment suggests that the maternal environment has a strong impact on how F1 seeds behave in response to temperature. When plants of each collection were grown in separate rooms of the greenhouse, so that outcrossing would not occur, germination of seeds from all collections was similar across the temperature gradient (Figure 2.2, bottom). Apparently, each collection had adapted to the common environmental conditions experienced by the parent plants in a single generation. Seeds collected from KY, New Carlisle and New
Knoxville, OH germinated readily at 5 C (Figure 2.2, top). These sites were the most southerly locations along our transect. Seedlings germinating at these sites in late fall when soil temperatures are low may succeed in reproducing. Seedlings germinating at the northern end of the transect in late fall under identical soil temperatures might not survive.
We have observed that common groundsel seedlings germinating at Wooster in late October and November rarely flower or survive until spring. Differences in germination observed in seeds collected from each site may reflect adaptation to local climate and levels of disturbance. Environments experienced by plants at each collection site probably varied
18 considerably. Average maximum temperatures during April 2000, the month prior to seed collection, were 7.2 C at Essexville, MI and 12.2 C at Lexington, KY.
19
100 Collected seeds
80
60
40
Germination (%)
20
0
100
80
60
40 Germination (%) Michigan Pemberville 20 Wooster N.Knoxville N.Carlisle
Common environment Kentucky 0 0 5 10 15 20 25 30 Temperature (C)
Figure 2.2: Cumulative germination of common groundsel seeds in response to constant incubation temperature for 15 days. Seeds were from plants collected from six locations (top) and from progeny of those plants grown in a common environment (bottom).
20 The germination response to temperature for seeds collected in 2002 differed from that for seeds collected in 2000 (Figure 2.3). Differences in germination response to temperature were not detected among sites. The optimum temperatures for germination were 15 and 20 C. Germination at 5 C varied only from 75 to 82%, and at 25 C the variation was from 65 to 78% among seeds from different sites. Germination at 30 C
(only tested on seeds collected in 2002) was between 0 and 10%. One reason for the difference in germination might be that seeds were collected a month later in 2002 than in
2000. The higher temperatures (Table 2.1) during seed development may have contributed to a reduction in conditional seed dormancy, as has been observed with other species (Baskin and Baskin 1998). The response at temperature extremes also differed in the two years, with differences among collection sites at low and high temperatures for seeds collected in 2000 but not for seeds collected in 2002.
2000 2002 Collection site April May May June Essexville, MI 7.2 15.2 11.2 20.7 Wooster, OH 9.5 16.9 13.3 21.6 Lexington, KY 12.2 19.4 18.8 23.6
Table 2.1: Monthly air temperatures (C) for 2000 and 2002 at different collection sites of common groundsel. Only collection sites with nearby weather stations are presented. Source: NOAA, 2003. National Climatic Data Center (www.ncdc.noaa.gov).
21
100
80
60
40
% germination %
20 Michigan Wooster Wilmington 0 Kentucky
0 5 10 15 20 25 30 35
Temperature (C)
Figure 2.3: Germination response of common groundsel under six constant temperatures for 2 weeks. Seeds were collected in June 2002 from four different locations in the Midwest (combined data for July and August 2002 replications).
22 Effect of maternal temperature and day-length on germination
Temperature and day-length altered the growth and development of common groundsel selections from Michigan and Kentucky, with no difference between seeds from the two locations or interactions between location and environment treatments
(Table 2.2). Plant height was greatest (38 cm) in the WLD environment, intermediate
(23.5 cm) in WSD and CLD conditions, and shortest (19 cm) in the CSD environment.
These results suggest that light duration and temperature both play a role in plant height determination, since short warm days produced plants with heights equal to those produced in long cold days. The pattern of plant dry weight with treatments did not correspond to that of plant height, with the greatest dry weight (160 mg/plant) produced by plants in CLD conditions, which was significantly different than that for plants grown in short day conditions (120-130 mg/plant). The number of inflorescences corresponded inversely to plant height, with the greatest number of inflorescences (44/plant) produced in CSD conditions and the fewest (27/plant) in WLD conditions. This suggests that there was a trade-off between shoot development and reproductive development, with plants growing in conditions similar to summer putting resources into height growth whereas those in conditions similar to autumn putting resources into reproduction. Plant height has implications for dispersal and population dynamics because taller plants tend to disperse seeds to greater distances than shorter plants (Andersen 1992). Resource allocation to height development at the expense of reproductive development in summer conditions reflects a strategy of favoring longer distance dispersal by fewer seeds,
23 whereas allocation to reproduction at the expense of height in autumn conditions favors the production of many seeds with low dispersal potential.
Seeds harvested from the plants growing in the four different environments exhibited different germination behavior (Figure 2.4). There was a significant effect of temperature (p<0.001), a marginally significant effect of day-length (p<0.03), and no interaction between temperature and day-length. Seeds produced in warm conditions were non-dormant at maturity, whereas those produced under cold conditions were mostly dormant. Seeds produced under warm conditions exhibited a peak of germination between 10 and 15 C, which is consistent with the previous studies. There was some evidence of a shift in the temperature response curve, with seeds produced under short days having higher germination rates under low temperatures and lower germination under high temperatures relative to seeds maturing under long days.
Results suggest that the survival strategy for plants growing under summer conditions of warm, long days, was to produce tall plants capable of dispersing non- dormant seeds to distant sites in an effort to reach suitable gaps that favor quick establishment of a second generation (Bergelson et al 1993). This is in contrast to plants produced in autumn conditions of cool, short days, whose more abundant inflorescences yielded dormant seeds with little potential for distant dispersal. These findings suggest that common groundsel plants alter their reproduction and dispersal strategy depending on growing conditions. Plants growing in autumn conditions favor dispersal in time by producing relatively more dormant seeds that can survive unfavorable conditions for germination. Plants growing in summer conditions favor dispersal in space by producing
24 relatively fewer seeds that are non-dormant but have greater potential for dispersal to sites where conditions are right for rapid regeneration.
Temperature Daylength Plant Height Dry weight Inflorescences cm mg number Warm Long days 38 a 150 ab 27 c Warm Short days 24 b 120 b 36 b Cold Long days 23 b 160 a 33 b Cold Short days 19 c 130 b 44 a
Table 2.2: Plant height, biomass, and inflorescence response of common groundsel to different growing conditions 42 days after sowing. Temperature settings were 15/8 or 22/15 C with an 8 h warm cycle. Photoperiods were 8/16 or 16/8-h light/dark. Light was 8-h core irradiance at 400 (±25) µmol m-2 s-1 PPFD. Photoperiod was extended in growth chambers set with a 16/8-h light/dark period by two 120-W incandescent bulbs that provided approximately 35(±5) µmol m-2 s-1 PPFD.
25 100 WLD WSD CLD CSD 80
60
40 Germination (%) Germination
20
0
0 5 10 15 20 25 30 35 Temperature (C)
Figure 2.4: Germination response of four types of common groundsel seeds to six constant temperature points. Seeds were from mother plants grown in four different environments, all with 8 h of warm cycle: 22/15 C and 16 h daylength (WLD); 22/15 C and 8 h daylength (WSD); 15/8 C and 16 h daylength (CLD); and 15/8 and 8 h daylength (CSD). Light was 8-h core irradiance at 400(±25) µmol m-2 s-1 PPFD. Photoperiod was supplemented in both cool and warm long daylength environments by two 120-W incandescent bulbs that provided approximately 35(±5) µmol m-2 s-1 PPFD. (Michigan and Kentucky, pooled data).
26 Detection of growth stage sensitive to thermal environment Since temperature was the maternal environmental factor that had the most impact on germination of F1 seeds, experiments were conducted to determine if sensitivity to this environmental signal varied with reproductive growth stage. There was a significant effect of location (Michigan and Kentucky maternal plants) and interactions between location and temperature treatments. There was also an interaction between growth stage and temperature treatments; therefore, these are separated in Figure 2.5. In control treatments, where the maternal environment was constant, plants from both locations growing in warm conditions produced seeds with near 100% germination, whereas those in cold conditions produced seeds with about 20-30% germination. This is consistent with the studies described above showing non-dormant seeds produced in summer conditions.
When mother plants were moved from warm to cold conditions, the germination response in F1 seeds depended on the growth stage at which this change occurred (Figure
2.5). The earlier this change occurred, the lower was the percent germination in F1 seeds.
Thus, when Kentucky mother plants were moved from warm to cold conditions at the bud stage, germination of F1 seeds was about 35%, whereas plants moved to cold conditions at fruit set produced seeds with nearly 100% germination. This was consistent for seeds from both locations, but was more pronounced for plants from Kentucky than those from Michigan. This suggests that the longer duration of exposure to cold in the mother plant, the more the seeds behaved like those from mother plants exposed to constant cold conditions. In Kentucky plants, exposure to cold from the bud stage
27 W-C Michigan P=0.05 C-W a 100 C-C a W-W ab 80 b
c c 60
Germination (%) Germination 40 d
d 20
0
Bud Anthesis Fruit set Controls
Kentucky 100 a a a
80 ab
bc 60 c
Germination (%) Germination 40 d d
20
0 Bud Anthesis Fruit set Controls
Figure 2.5: Germination of common groundsel seeds originating from plants collected at Essexville (MI) and Lexington (KY) and later grown in constant and non-constant thermal environments. WW= plants grown continually at 22/15 C; CC= plants grown continually at 15/8 C; WC=plants grown at 22/15 C and transferred to 15/8 C at the designated growth stage until seed maturation; CW=plants grown at 15/8 and transferred to 22/15 C at the designated growth stage until seed maturation. 28 through maturity produced seeds with germination equivalent to constant cold controls.
For plants from both locations, exposure to cold during fruit development produced seeds with germination equivalent to those that were constantly in warm conditions.
For mother plants moved from cold to warm conditions, there was a significant difference in F1 seed germination between Michigan and Kentucky plants (Figure 2.5).
The Kentucky plants produced seeds with higher germination (90%) when moved at fruit set compared to those moved at the bud stage (65%). In contrast, the Michigan plants moved from cold to warm conditions during fruit set produced seeds with lower germination (35%) than those moved at the bud and anthesis stages (~60%).
These results show a clear effect of maternal environment on the behavior of progeny. This was apparent in the differences between Michigan and Kentucky plants, and among seeds produced on mother plants growing in different environments. The difference between Michigan and Kentucky seeds was most evident in plants moving from cold to warm environments during seed development (Figure 2.5). This suggests a different adaptation among common groundsel plants from Michigan, where the growing season is shorter and cold temperature extremes are greater than in Kentucky. This might reflect inherited differences between plants from these two locations, or it might be due to effects of the maternal environments (i.e. Kentucky vs Michigan) carried over to the seeds of the next generation.
Results of these studies demonstrate several roles of temperature in modifying the germination of common groundsel. Even though seeds of this species have an obligate requirement for light to terminate dormancy so that germination can proceed (Hilton
29 1983), the dormancy level of seeds and consequent percent germination is modified by temperature in various ways. Temperature alters seed germination directly in the familiar germination response curve (Figure 2.2) with a broad optimum temperature for germination and decreasing germination at temperature extremes. Temperature also affected the germination response of seeds indirectly by altering the physiology of seeds produced on plants exposed to varying growth conditions. Maternal temperature conditions were more important than day-length in determining the physiological status of F1 seeds. Highly dormant seeds were produced in cool temperature conditions and non-dormant seeds were produced in warm conditions regardless of day-length (Figure
2.4). Temperature conditions of the maternal environment also altered the germination response of common groundsel seeds from plants collected at Essexville (MI) and
Lexington (KY) and later grown in constant and non-constant thermal environments.
Plants in constant cold and warm environments produced seeds that were highly dormant and non-dormant, respectively, at maturity (Figure 2.5). Changing temperature conditions from warm to cold during reproductive development increased seed dormancy, especially the earlier the change in temperature occurred during development. However, the impact of moving plants from a cold to a warm environment depended on the source of the maternal plants (Michigan vs Kentucky) and the time during development that environmental conditions changed. The dominant role of temperature in determining germination behavior is typical of plants that function both as winter and spring annuals
(Fenner 1991, Gutterman 2000). This adaptation allows common groundsel to alter its
30 reproductive strategy depending on when seeds are produced, and is probably a critical factor that allows for multiple generations in a calendar year.
LITERATURE CITED
Andersen, M. C. 1992. An analysis of variability in seed settling velocities of several wind-dispersed asteraceae. Am. J. Bot. 79:1087-1091.
Baskin, C. C. and J. M. Baskin 1998. Seeds: ecology, biogeography, and evolution of dormancy and germination. San Diego, Academic Press: 666.
Belderok, B. 1961. Studies on dormancy in wheat. Proceedings International Seed Testing Association 26: 697-760.
Bergelson, J., J. A. Newman, and E. M. Foresroux. 1993. Rates of weed spread in spatially heterogeneous environments. Ecology 74: 999-1011.
Britton, N. L. and A. Brown 1898. An Illustrated Flora of the Northern United States, Canada and the British Possessions. New York, Charles Scribner's Sons.
Dorne, C. J. 1981. Variation in seed germination inhibition of Chenopodium bonu- henricus in relation to altitude of plant growth. Canadian Journal of Botany 59: 1893-1901.
Fenner, M. 1991. The effects of the parent environment on seed germinability. Seed Science Research 1: 75-84.
Figueroa, R. and D.J. Doohan. 2002. Germination response of six common groundsel (Senecio vulgaris L.) weed collections to temperature and burial. WSSA Abstracts 42: 82-83.
Gutterman, Y. 1973. Differences in the progeny due to daylenght and hormonal treatment of the mother plant. Seed ecology. W. Heydecker. Butterworth, London: 59-80. 31 Gutterman, Y. 1978. Germinability of seeds as a function of the maternal environments. Acta Horticulturae 83: 49-55.
Gutterman, Y. 1992. Maturation dates affecting the germinability of Lactura serriola L. achenes collected from a natural population in the Negev Desert highlands: germination under constant temperatures. Journal of Arid Environments 22: 353- 362.
Gutterman, Y. 2000. Maternal effects on seeds during development. Seeds: The ecology of regeneration in plant communities. M. Fenner, CABI Publishing: 59-84.
Gutterman, Y. and M. Evenari. 1972. The influence of day lengthton seed coat color, an index of water permeability of the desert annual Onomis siculaGuss. Journal of Ecology 60: 713-719.
Harrington, J.L. and R. C. Thompson, 1952. Effect of variety and area of production on subsequent germination of lettuce seed at high temperatures. Proceedings American Society of Horticultural Science 59:445-450.
Heide, O. M., O. Juntila and R. T. Samuelsen. 1976. Seed germination and bolting in red beet as affected by parent plant environment. Physiologia Plantarum 36: 343-349.
Hilton, J. R. 1983. The influence of light on the germination of Senecio vulgaris L. New Phytologist 94: 29-37.
Holm, L., J. Doll, E. Holm, J. Pancho and J. Herberger 1997. World Weeds: Natural histories and distribution. New York, United States, John Wiley & Sons, Inc.:740- 750
Junttila, O. 1973. Seed and embrio in Syringa vulgaris and S. reflexa as affected by temperature during seed development. Physiologia Plantarum 29: 264-268.
Kigel, J., M. Ofir and D. Koller. 1977. Control of the germination responses of Amaranthus retroflexus L. seeds by their parental photothermal environment. Journal of Experimental Botany 28: 1125. 32 Mallory Smith, C. 1998. Bromoxynil-resistant common groundsel (Senecio vulgaris). Weed Technology 12(2): 322-324.
Popay, A. I. and E. H. Roberts. 1970a. Ecology of Capsella bursa-pastoris (L.) Medik. and Senecio vulgaris L. in relation to germination behaviour. Journal of Ecology 58(1): 123-129.
Popay, A. I. and E. H. Roberts. 1970b. Factors involved in the dormancy and germination of Capsella bursa-pastoris (L.) Medik. and Senecio vulgaris L. Journal of Ecology 58(1): 103-122.
Ren, Z. and R. J. Abbott. 1991. Seed dormancy in Mediterranean Senecio vulgaris L. New Phytolologist 117(4): 673-678.
Roberts, H. A. 1964. Emergence and longevity in cultivated soil of seeds of some annual weeds. Weed Research 4:296 - 307.
Robinson, D. E., O'Donovan, j. T., Sharma, M. P., Doohan, D. J. and R. Figueroa. 2003. The biology of Canadian Weeds. 123. Senecio vulgrais L. Canadian Journal of Plant Science 83 : 629-644.
Ryan, G. F. 1970. Resistance of common groundsel to simazine and atrazine. Weed Science 18(5): 614-616.
SAS 2000. Statistical Analysis Systems User's Guide, version 8.1. Cary, NC, USA, SAS Institute Inc: 1686.
Senesac, A. 1991. Common groundsel Senecio vulgaris L. Long Island Hortic News. Riverhead, N.Y. : Cornell Cooperative Extension
Steel, R. G. D., J. H. Torrie and D. A. Dickey. 1997. Principles and Procedures of Statistics: A Biometrical Approach. New York, McGraw-Hill: 666.
33 Swanton, C. J., J. Z. Huang, A. Shrestha, M. Tollenaar, W. Deen and H. Rahimian. 2000. Effects of temperature and photoperiod on the phenological development of barnyardgrass. Agronomy Journal 92: 1125-1134.
Tollenaar, M. 1999. Duration of the grain -filling period in maize is not affected by photoperiod and incident PPFD during vegetative phase. Field Crop Research 65: 15-21.
VonAbrams, G. J. and M. E. Hand. 1956. Seed dormancy in Rosa as a function of climate. American Journal of Botany 43: 7-12.
34 CHAPTER 3
COMMON GROUNDSEL SEED LONGEVITY AND SEEDLING EMERGENCE
ABSTRACT
Common groundsel (Senecio vulgaris) is an alien annual weed that has become increasingly troublesome in many crops in Ohio. Understanding the periodicity of seedling emergence and longevity of seeds buried in the soil may help growers devise more efficient strategies to control common groundsel. Studies were conducted to determine the dormancy status of common groundsel seeds over 24 months, and to describe the effect of tillage and fertilizer on the pattern of seedling emergence and the rate of depletion of seeds from the soil seed bank. Common groundsel seeds were collected (June 2000 and 2002) from sites along a 700 km transect from Lexington, KY to Essexville, MI (39° 1’ and 43° 36’ N, respectively). Seeds were cleaned and placed in nylon mesh bags for burial in a common garden. Every month for the following 24 months, replicate bags from each location were exhumed, starting July 2000 and ending
June 2002. Germination was tested under alternating temperatures of 20 and 10 C, for 14 and 8 h day/night, respectively. Germination response at each sampling date was similar regardless of seed source, but differed for 2000-02 and 2002-04 experiments. Laboratory
35 germination of seeds buried in June 2000 was initially high (98%) and declined rapidly to about 20% by mid-winter. Germination increased to about 60% during the second summer followed by a slow decline to 40% during winter and another rapid decline before the third summer. The rapid declines in germination were preceded by low soil temperatures (< 5 C) and the germination peaks corresponded with periods of high soil temperatures (~20 C). Results suggested that common groundsel follows a cycle of dormancy and non-dormancy corresponding to decreases and increases, respectively, in soil temperature. Nearly all the buried seeds germinated or died during two years of deep burial in undisturbed soil, suggesting that common groundsel seeds may not persist more than a few months in regularly disturbed soils. Results indicate that elimination of common groundsel from the seed bank requires shallow tillage and moderate irrigation when necessary to stimulate emergence.
36 INTRODUCTION
Common groundsel (Senecio vulgaris), a native of Mediterranean Europe, has spread throughout many of the temperate regions of the world (Aldrich-Markham 1994).
The weed has become very successful in many crops including forages, cereals, mint, berries, ornamentals, and vegetables (Norris 1973; Agamalian 1983; Holm et al. 1997). In
Ohio, common groundsel has increased in importance in ornamental plant nurseries and berry fields during the past 10 years. Control is complicated by tolerance to several herbicides (Anonymous 1999; Doohan and Figueroa 2001) and resistance to others (Ryan
1970; Radosevich and Devilliers 1976; Fuerst 1984; Mallory Smith 1998; Beuret 1989).
An important factor determining the success of species like common groundsel is the seasonal pattern of seedling emergence, which determines the association of the weed with particular cropping systems (Brenchley and Warrington 1930), and has a bearing on weed management decisions (Roberts and Chancellor 1979). A report by Roberts (1982) suggested that common groundsel germinates under a wide range of environmental conditions and emerges continuously throughout the growing season. Flushes of emergence in early summer and autumn occurred soon after seed dispersal and did not appear to correspond to environmental stimuli (Roberts 1982).
Another factor determining the success of a weed is the persistence of buried seeds, a characteristic that is a great advantage to annual weeds that respond to periodic soil disturbance. Longevity is influenced by several factors, including the physiological status of seeds, the chemical and physical environment where seeds reside, and the position of seeds relative to the soil surface (Baskin and Baskin 1998). Common
37 groundsel seeds were not included in any of the classic seed longevity studies, so persistence can only be estimated from short-term germination experiments.
Nevertheless, the persistence of common groundsel seeds is considered to be relatively brief compared with many other annual weeds (Baskin and Baskin 1998). At maturity, most common groundsel seeds germinate readily (Popay and Roberts 1970a), but viability decreases rapidly under field conditions (Robinson et al. 2003). Roberts and
Feast (1973) reported that seed germination was the main cause of seed loss from the seed bank, with 31% and 11% of seeds germinating in the first year after burial where soil was cultivated and undisturbed, respectively. After 6 years, 0.3% of buried seeds were still viable in the cultivated soil, whereas 13% remained viable in undisturbed soil
(Roberts and Feast 1973).
Benech-Arnold et al. (2000) have suggested that some environmental factors
(temperature and water potential) modify the dormancy level of seeds whereas other factors (light, nitrate, and temperature fluctuation) act to terminate dormancy. In common groundsel, germination of initially dormant seeds was 4% at 4 C and increased to 96% at
10 C (Popay and Roberts 1970a). In a similar study, germination over 6 wk increased from 17% to 69% as temperature increased from 5 C to 25 C (Rozijn and van Andel
1985). These authors also indicated that dry storage for 10 wk at 35 C reduced seed dormancy so that 100% of seeds germinated at incubation temperatures from 10 to 25 C.
Common groundsel seeds generally require light to terminate dormancy prior to germination (Hilton 1983), although Popay and Roberts (1970b) reported a small proportion of seeds (35%) capable of germinating in the dark at 10 C. Hilton (1983)
38 showed that seeds had a strong requirement for white or red light to attain maximum germination (98%) at 20 °C, but the light requirement could be overcome by treatment with gibberellic acid or KNO3. Exposed to light, common groundsel seeds do not have a stratification requirement, but germination was stimulated in seeds kept in darkness for 2 wk at 4 C (Popay and Roberts 1970a). Nondormant seeds lost the ability to germinate when buried due to absence of light and to elevated CO2 levels (Popay and Roberts
1970a). However, night cultivation did not reduce common groundsel emergence compared with daytime cultivation (Fogelberg 1999) and emergence was equivalent in chisel-plow and ridge till systems where seeds had been buried 5 cm deep (Clements et al. 1996). Once dormancy was terminated by light, seeds required a temperature of 4 C to initiate germination, with maximum germination recorded at 20 to 25 C, and a steep decline in germination above 31 C (Popay and Roberts 1970a; Ren and Abbot 1991;
Thompson et al 1997).
Karssen (1980) buried ripe, non-dormant common groundsel seeds in November and measured changes in their dormancy over a 2 yr period. Seeds were exhumed every 2 or 3 months. Their non-dormant condition was maintained until late spring and early summer when they developed a deep dormancy. This led to a complete loss of germination, which was not resumed until the following January. However, Popay and Roberts (1970a) found no change in germination (100%) over 21 months in seeds buried in December.
In preliminary observations of common groundsel in nurseries and strawberry fields in Ohio we noted an intermittent pattern of emergence coinciding with rainfall events, which contrasts sharply with Roberts's (1964) finding that emergence was
39 associated only with seed dispersal events. However, when freshly produced common groundsel seeds were deposited in a local methyl bromide fumigated strawberry field, nearly 100% of the seeds germinated within a few weeks (Felix and Doohan 2003). This observation suggests that the local biotype of common groundsel produces seeds that are not dormant at maturity.
Documenting periodicity of emergence and longevity of seeds buried in the soil and understanding how these interact may help weed managers devise new or improved strategies to control common groundsel. This research was conducted to provide more understanding of seed dormancy, longevity and germination patterns of common groundsel under conditions common to the Midwest. The objectives of these studies were to determine the dormancy status of common groundsel seeds over 24 months, and to describe the effect of tillage and fertilizer on the pattern of seedling emergence and the rate of depletion of seeds from the soil seed bank.
MATERIALS AND METHODS
Burial studies
Common groundsel seeds were collected in June 2000 from 6 sites along a 700 km transect from Lexington, KY (39° 1’) to Essexville, MI (43° 36’ N). At each site, seeds were collected from 35 plants, selected at random, within 1 ha. Collection sites were Bay
Landscaping Inc, Essexville, MI; Hillenmeyer nurseries, Lexington, KY; Manbeck Nursery,
New Knoxville, OH; Scarff’s Nursery, New Carlisle, OH; North Brach Nursery,
Pemberville, OH and Maurer Farm, Wooster, OH. Seeds were cleaned by gently rubbing
40 them through sieves (2380, 1000, and 500 micron openings) to remove the pappus and all flower structures. Seeds from each site were stored separately in paper bags on the laboratory bench for a week at room temperature (20 ± 2 C).
A field study to investigate changes in groundsel seed dormancy over time was established on the Horticultural Farm at the Ohio Agricultural Research and Development
Center (OARDC) in Wooster in June 2000. The soil was a Canfield silt loam (Oxyaquic
Fragiudalf) with 2% organic matter and pH of 5.5. Common groundsel seeds from each site were placed in nylon mesh bags, with 100 (+ 10) seeds per bag and 96 bags per location.
Seed bags were buried 10 cm deep and two passes of a hand pushed roller was used to pack the soil. Soil temperature at 5 cm depth was recorded hourly throughout the year using a thermocouple soil temperature probe and recorder1 in the middle of the experimental area.
The experiment was arranged as a split plot with 24 main plots (60 x 100 cm) arranged in a completely randomized block design with four replications. The main plots were assigned to
24 sampling dates, and subplots consisted of six seed bags (one from each collection site).
Every month for the following 24 months, replicate bags from each location were exhumed, starting July 2000 and ending June 2002. Germination was tested in 4.7-cm petri dishes containing two Whatman2® #5 filter papers, previously moistened with 1 ml of distilled water. Fifty randomly selected seeds from each seed bag were equally spaced on a petri dish. The dishes were placed in an incubator with alternating temperatures of 20 and 10 C, for 14 and 8 h day/night, respectively. White fluorescent light (25 ± 5 µmol m-2 s-1) was
1 Onset computer corporation, 470 Macarthur Blvd., Bourne, MA, 02532.
2 Whatman International Ltd. Maidstone, England.
41 supplied during the high temperature period. Seeds were counted as germinated if the radicle had protruded the seed coat. Germination was recorded every other day for two wk.
Germinated seeds were removed from the Petri dishes as they were counted.
The entire experiment was repeated in June 2002, with new seeds collected from a sub-set of the original sites: MI (Essexville), KY (Lexington) and OH (Kingsville and
Wooster).
Data were subjected to ANOVA using the GLM procedure in SAS to determine significance of main effects and their possible interactions. The SAS REG procedure was used for each seed source to calculate regression functions and ANCOVA was used to determine if differences between slopes were significant. Pooled means by locations were then plotted using Sigma plot 8.03 software.
Seedling emergence studies
Field experiments were conducted at Kingsville, Ohio on a site with a history of common groundsel infestation. Soil was a Bogart loamy fine sand (Aquic Hapludalf) with pH of 6.0 and 1.8% organic matter. The experiment was conducted between April and October in 2002 and 2003 in different locations within the same field. The same treatment arrangement was used each year. All plots were prepared with two passes of a field cultivator approximately 7 cm deep on April 24 and September 17 to eliminate existing vegetation and stimulate spring and fall seed germination.
3 Sigma Plot 2002 for Windows Version 8.0, SPSS Inc., 233 S. Wacker Dr., Chicago, IL 60606.
42 A factorial set of treatments (2 levels of tillage x 2 levels of fertilizer) was applied to plots (2 x 2 m) in a randomized complete block design with four replications. The two tillage levels were: no tillage after the April and September field cultivations (designated
‘infrequent soil disturbance’), and additional tillage (5 cm deep) with a garden rake every other week (designated ‘frequent soil disturbance’). The two levels of fertilizer were 0 and 40 kg/ha potassium nitrate applied and mixed with the soil just after the April and
September tillage events.
Emerged seedlings were counted and removed from the plots every week from
May 1 to October 16. Temperatures and rainfall were recorded using a thermocouple with data-logger buried at 5-cm depth and a rain gauge with an overflow chamber.
Emergence data were analyzed using the GLM procedure in SAS, with years and sampling dates within years subjected to repeated measurement ANOVA. Treatments and their interactions were tested using SAS MIXED procedure followed by a chi-square test for each model component. Treatment means were plotted using Sigma plot software.
Homogeneity of variance assumption for ANOVA was fulfilled for all treatments and years without need of data transformation. All F tests were conducted with p=0.05 and means between treatments separated by protected orthogonal contrast at p=0.05. Logistic regression analysis (using the GENMOD procedure) was conducted to develop an equation to predict the probability of a common groundsel emergence event based on temperature and rainfall data.
43 The probability of emergence was calculated using the logistic model described by Agresti (2002):
log (p / 1-p) = α + τi + β * Rainfall [1] where P = probability of emergence; α = intercept; τi = temperature; β = rainfall coefficient; and Rainfall= cumulative weekly rainfall (cm).
Artificial seed bank experiments
Experimental sites were selected at OARDC in Columbus and Wooster OH in fields that were considered to be free of common groundsel. In a preliminary study, no common groundsel seedlings were found in soil sampled from these fields after two months of exhaustive germination in the greenhouse. Soil at Columbus was a Crosby silt loam soil
(Aeric Epiaqualf) and at Wooster a Canfield loam (Oxyaquic Fragiudalf). Organic matter was 2.5 and 2.8% and pH was 5.5 and 6.2, at Columbus and Wooster, respectively. The
Columbus site had a previous five-year history of vegetables, rotated with canola and sunflower. The Wooster site had been planted with wheat, soybean, and corn followed by corn.
Common groundsel seeds used in these experiments were collected in June, 2001, from the Secrest Arboretum (Wooster, OH), and stored in the laboratory at room temperature until use. In August 2001, each site was plowed, disked, and rototilled. Seeds were sown in 2 x 2 m plots on September 6, 2001, using a saltshaker to deliver about 3,000 seeds/m2, which approximates the average seed bank size reported by Roberts and
Chancellor (1968).
44 The experiment was a 2 x 2 factorial with two levels of tillage and two levels of fertilizer. The experimental design was a randomized complete block with four replications. Levels of tillage were infrequent soil disturbance and frequent soil disturbance (5 cm deep) with a garden rake every week. The two levels of fertilizer were
0 and 40 kg/ha potassium nitrate applied and mixed with the soil just after common groundsel seeds were scattered. Wheat straw (4.0 ± 0.5 kg/ plot) was spread on each plot to reduce soil erosion and seed movement, and to promote uniform seedling establishment. Ten days after seeding, the straw cover was carefully removed. Between- plot alleys were sown with oat (112 kg /ha) in September, and mowed as needed during the growing season. To avoid possible movement of new seeds into the experimental area, common groundsel was controlled within a 50-m isolation zone around each site.
Common groundsel seedling emergence was evaluated weekly from planting through July of the following year. Seedlings were counted in a 50- by 50-cm quadrat, placed in the center of each plot. Seedlings were removed from the plots as they were counted.
In August 2002, five soil cores (2 cm dia., 15 cm deep) were systematically sampled from the center square meter of each plot and moved into a greenhouse to quantify remaining common groundsel seeds by repetitive exhaustive germination. The whole experiment was repeated from August 2002 until July 2003.
Emergence counts were analyzed using the GLM procedure in SAS, with years and sampling dates within years as repeated measures. Treatments and their interactions were tested using SAS MIXED. All F tests were conducted with p=0.05 and means
45 between treatments separated by protected orthogonal contrast at p=0.05. Treatment means were plotted using Sigma plot software. Homogeneity of variance assumption for
ANOVA was fulfilled for all treatments and years without need of data transformation.
RESULTS AND DISCUSSION
Burial studies
Germination response at each sampling date was similar regardless of seed source, but differed for 2000-02 and 2002-04 experiments. The ANOVA did not indicate enough evidence (P=0.0575) of differences between locations, allowing the use of pooled means by sources (Figure 3.1). Laboratory germination of seeds buried in June 2000 was initially high (98%) and declined rapidly to about 20% by mid-winter. Germination increased to about 60% during the second summer followed by a slow decline to 40% during winter and another rapid decline before the third summer. Low soil temperatures
(<5 C) preceded the rapid declines in germination and periods of high soil temperatures
(~20 C) preceded the germination peaks.
Seed dormancy was not observed initially after burial in late spring and early summer 2000, but increased over time reaching maximum dormancy at the end of winter
2001. At the beginning of spring, germination recovered to 60% indicating release of dormancy. Results from 2000-02 are similar to the study by Karssen (1980) where seeds buried in November increased in dormancy with elevated temperatures. Germination declined to less than 10% by the end of March 2002 at which time achenes appeared
46 empty and light in color indicating death. This seed mortality has been documented in various species (Baskin and Baskin 1998).
A similar pattern was observed in the seeds buried in 2002, but with a narrower range of germination. Dormancy was not detected soon after burial but increased during fall as reflected by decreased germination throughout that season. A slight increase in germination at the end of winter 2003 indicated release from dormancy. During spring
2003 the slope of seed germination became more negative, reaching a plateau of approximately 60% during the summer months.
47
100 Germination (%) Soil temperature (C) Burial date
80
60
40
20
0
Jun/00 Dec/00 Jun/01 Dec/01 Jun/02 Dec/02 Jun/03 Dec/03
Figure 3.1: Germination of common groundsel seeds after burial in the field and incubation at 20/10 C and 14 h of white fluorescent light.
48 Seedling emergence studies
The pattern of seedling emergence from soil naturally infested with common groundsel varied with years and soil disturbance within years but no fertilizer effect or interaction among these variables was detected. The absence of a fertilizer effect might be due to the relatively low rate applied and the sandy soil.
In 2002 soil disturbance stimulated emergence in May, and after two soil disturbance events the cumulative emergence differed between the two levels of soil disturbance (Figure 3.2). From July through August significant emergence did not occur, including those plots disturbed every other week, suggesting that emergence was probably limited by high soil temperatures (mean = 27 C). Rainfall was generally low during summer, but there were substantial rainfall events that were not followed by flushes of common groundsel emergence. Soil disturbance in all plots in early September stimulated emergence, which continued through the end of that month. Cumulative emergence leveled off in October in spite of abundant rainfall and temperatures (10-20 C) that were in an appropriate range for common groundsel germination.
In 2003 the second soil disturbance resulted in greater seedling density (450 m-2) than in plots that had only by disturbed one time (310 m-2) (Figure 3.3). Thereafter, cumulative emergence differed between frequently and infrequently disturbed plots for the remainder of the study. Seedlings counted in the infrequently disturbed plots averaged about 100 m-2 for the period of June through August despite abundant rainfall. In contrast about 260 seedlings m-2 emerged during this period where soil was disturbed every two weeks. The temperature averaged about 5 C lower and rainfall 31 cm higher in
49 2003 than in 2002, which probably accounts for the difference in emergence patterns between the two years. With the more abundant rainfall in 2003, soil disturbance appeared to stimulate emergence even when average weekly temperatures exceeded 27 C.
50 1000 Infrequent soil disturbance Frequent soil disturbance Soil disturbance event
800 * ** * * * * * * * -2 600 *
400
Seedlings m
200
* = p<0.05
0
20 35 pp Soil temp 30
15 25
20
10 15 Rainfall (cm) Rainfall
10 Soil (C) temperature 5
5
0 0 May Jun Jul Aug Sep Oct Nov Dec 2002
Figure 3.2: Cumulative emergence of common groundsel in response to soil disturbance at Kingsville, Ohio during 2002. Frequent soil disturbance plots ( ) were raked every other week. Infrequent soil disturbance plots ( ) were cultivated only twice each year (April and September). 51 1000 Infrequent soil disturbance Frequent soil disturbance Soil disturbance event 800 * *** ** * * * -2 600 * * * * * * * * * * * * * 400 * * Seedlings m
200 * = p<0.05 0
20 35
pp Soil temp 30
15 25
20 10 15 Rainfall (cm)
10 (C) temperature Soil 5
5
0 0 May Jun Jul Aug Sep Oct Nov Dec 2003 Figure 3.3: Cumulative emergence of common groundsel in response to soil disturbance at Kingsville, Ohio during 2003. Frequent soil disturbance plots ( ) were raked every other week. Infrequent soil disturbance plots ( ) were cultivated only twice each year (April and September). 52 The logistic regression analysis generated two equations, one for frequently disturbed plots and one for infrequently disturbed plots (Table 3.1). The probability of emergence was highly predictable (p < 0.01) based on weekly average soil temperature and rainfall in both levels of disturbance. The equations describe the probability of emergence based on rainfall during periods when the average soil temperature is between the limits of 5 and 25 C; outside these temperature limits the probability of emergence was assumed to be zero (Figueroa and Doohan 2002). The infrequently disturbed plots required 0.52 cm of rainfall during the previous week for a 50% probability of emergence; whereas, the frequently disturbed plots required only 0.06 cm of rainfall for this probability of emergence. This finding is also evident in the cumulative emergence curves (Figures 3.2 and 3.3), where emergence in infrequently disturbed plots occurred only after large rainfall events, while emergence was stimulated by relatively low rainfall as long as the soil was disturbed. These results suggest that in no-till cropping systems a high rainfall threshold would be required before flushes of emergence would occur; otherwise, seeds will remain in the seed bank to germinate later or be subject to other sources of mortality. Tillage, to deplete the seed bank, should be effective in stimulating emergence as long as the soil is within the 5 to 25 C soil temperature limits.
53
Tillage levels α + τi β Rainfall (cm)
Frequent soil disturbance -0.0102 0.1665 0.061
Infrequent soil disturbance -0.0676 0.1310 0.516
Table 3.1: Parameters for common groundsel emergence equations and rainfall needed for 50 % probability of emergence of two soil disturbance levels. Equations for probability were calculated using the logistic model: log [p/(1-p)]= α + τi + β * Rainfall; where p = probability of emergence; α = intercept; τi = temperature; β = rainfall coefficient; and Rainfall= cumulative weekly rainfall.
54 Artificial seed bank experiments The artificial seed bank study allowed us to examine the fate of freshly matured common groundsel seeds produced on plants that germinated in spring and set seeds in summer. In contrast to the other emergence studies, the density of seeds in the soil was known (3000 m-2) at the start of the experiment. Statistical analysis indicated no significant difference due to year, fertilizer, or soil disturbance level; therefore, data were averaged over all these factors for presentation in Figure 3.4. Immediately after seeding there was an immediate and precipitous increase in seedling emergence, representing about 50% of the seeds in the seed bank. This was followed by only about 20% additional emergence over the next 38 weeks. After 40 weeks, a soil sample was taken from all plots and a standard greenhouse germination test was conducted to determine the density of remaining viable germinable seeds. No seedlings appeared in these samples from any treatment in either year, suggesting that about 30% of the original seed population was lost to sources of mortality other than emergence, such as predation, decay, or fatal germination (Zorner et al. 1984).
Our data indicate that common groundsel follows a cycle of dormancy and non- dormancy in-step with decreases and increases, respectively, in soil temperature. The general pattern corresponds with that of winter annuals in which seasonal cycles of warm and cold soil temperatures, respectively break and induce seed dormancy (Baskin and
Baskin 1998). Virtually all buried seeds germinated or otherwise died during two years of deep burial in undisturbed soil. Data from seedling emergence studies and artificial seedbank experiments indicate that common groundsel seeds may not persist in
55 significant numbers beyond a few months in regularly disturbed soils. Infrequent rainfall and high soil temperatures (>25C) may enforce dormancy somewhat, possibly extending the life of the seed bank especially in soils that are rarely disturbed. These results indicate that eradication of common groundsel from the seedbank might be done with relative ease, utilizing shallow tillage and moderate irrigation when necessary to stimulate emergence. However, additional studies should be conducted with seeds ripened under cool conditions of fall and winter to document similar or different physiology.
56
100
-3 80 Y = 111.7(1-e2.4x10 )0.057 2 R = 0.985
60
40 % Cumulative emergence emergence Cumulative% 20
0
0 4 8 32 36 40 Weeks
Figure 3.4: Percent cumulative emergence of common groundsel from an artificially seeded seedbank in August 2001 and 2002.Seedlings were removed after counting. Data presented has been combined across years and two locations (Columbus and Wooster, Ohio).
57 LITERATURE CITED
Agamalian, H. S. 1983. Competition of annual herbs in broccoli. Proceedings of the Western Society of Weed Science 36:192.
Agresti, A. 2002. Categorical data analysis. New York, John Wiley & Sons, Inc.: 84-97.
Aldrich Markham, S. 1994. Common groundsel: Senecio vulgaris L. PNW(466): 4.
Anonymous 1999. Guide to weed control. Table 21: Classification of weeds according to response to various foliage sprays. Toronto, Ontario Ministry of Agriculture, Food and Rural Affairs. Queen's Printer for Ontario.: 277.
Baskin, C. C. and J. M. Baskin 1998. Seeds: ecology, biogeography, and evolution of dormancy and germination. San Diego, Academic Press: 27-47
Benech-Arnold, R. L., R. A. Sanchez, F. Forcella, B. C. Kruk and C. M. Ghersa. 2000. Environmental control of dormancy in weed seed banks in soil. Field Crops Research 67: 105-122.
Beuret, E. 1989. A new problem of herbicide resistance: Senecio vulgaris L. in carrot crops treated with linuron. Revue Suisse de Viticulture, d'Arboriculture et d'Horticulture 21(6): 349-352.
Brenchley, W. E. and K. Warrington. 1930. The weed seed population on arable soil. I Numerical observation of viable seeds and observations on their natural dormancy. Journal of Ecology 18: 235-272.
Clements, D. R., D. L. Benoit, S. D. Murphy and C. J. Swanton. 1996. Tillage effects on weed seed return and seedbank composition. Weed Science 44: 314-322.
Doohan, D. J. and R. Figueroa. 2001. Biology and control of common groundsel in strawberry. 2002 Ohio Fruit and Vegetable Growers Congress/Ohio Roadside Marketing Conference., Toledo, Ohio.
58 Felix, J. and D. J. Doohan. 2003. Recovery of weed seedbank after methyl bromide fumigation. Proceedings of the North Central Weed Science Society. December 2003. Louisville, KY. Abstract 57.
Figueroa, R. and D.J. Doohan. 2002. Germination response of six common groundsel (Senecio vulgaris L.) weed collections to temperature and burial. WSSA Abstracts 42: 82-83.
Fogelberg, F. 1999. Night-time soil cultrivaiuon and intra-row brush weeding for weed control in carrots (Daucus carota). Biol. Agric. Hortic. 39: 469-479.
Fuerst, E. P. 1984. Effects of inhibitors and diverters of photosynthetic electron transport on herbicide resistant and susceptible weed biotypes. Dissertation Abstracts International, B Sciences and Engineering 45(4): 1079b-1080b.
Hilton, J. R. 1983. The influence of light on the germination of Senecio vulgaris L. New Phytologist 94(1): 29-37.
Holm, L., J. Doll, E. Holm, J. Pancho and J. Herberger 1997. World weeds: natural histories and distribution. New York, John Wiley & Sons, Inc:740-750.
Karssen, C. M. 1980. Patterns of change in dormancy during burial of seeds in soil. Israel Journal of Botany 29: 65-73.
Mallory Smith, C. 1998. Bromoxynil-resistant common groundsel (Senecio vulgaris). Weed Technology 12(2): 322-324.
Norris, R. 1981. Weed competition in seedling alfalfa. 31st Weed Science Society of America Conference.
Popay, A. I. and E. H. Roberts. 1970a. Ecology of Capsella bursa-pastoris (L.) Medik. and Senecio vulgaris L. in relation to germination behaviour. Journal of Ecology 58 (1): 123-129.
59 Popay, A. I. and E. H. Roberts. 1970b. Factors involved in the dormancy and germination of Capsella bursa-pastoris (L.) Medik. and Senecio vulgaris L. Journal of Ecology 58 (1): 103-122.
Radosevich, S. R. and O. T. Devilliers. 1976. Studies on the mechanism of s-triazine resistance in common groundsel. Weed Science 24(2): 229-232.
Ren, Z. and R. J. Abbott. 1991. Seed dormancy in Mediterranean Senecio vulgaris L. New Phytolologist 117(4): 673-678.
Roberts, H. A. 1964. Emergence and longevity in cultivated soil of seeds of some annual weeds. Weed Research 4: 296-307.
Roberts, H. A. 1982. Seasonal patterns of weed emergence. Asp. Appl. Biol. 1: 153 - 154.
Roberts, H. A. and R. J. Chancellor. 1968. The changing population of viable weed seeds in an arable soil. Weed Research 8: 253-256.
Roberts, H. A. and R. J. Chancellor. 1979. Periodicity of seedling emergence and achene survival in some species of Carduus, Cirsium and Onopordum. Journal of Applied Ecology 16(2): 641-647.
Roberts, H. A. and P. M. Feast. 1973. Emergence and longevity of seeds of annual weeds in cultivated and undisturbed soil. Journal of Applied Ecology 10: 133 - 143.
Robinson, D. E., O'Donovan, J. T., Sharma, M. P., Doohan, D. J. and R. Figueroa. 2003. The biology of Canadian Weeds. 123. Senecio vulgrais L. Canadian Journal of Plant Science 83 : 629-644.
Rozijn, N. A. M. G. and J. Van Andel. 1985. Analysis of the germination syndrome of dune annuals. Flora 177: 175-185.
Ryan, G. F. 1970. Resistance of common groundsel to simazine and atrazine. Weed Science 18 (5): 614-616. 60 Thompson, A. J., Jones, N. E. and Blair, A. M. 1997. The effect of temperature on viability of imbibed weed seeds. Ann. Appl. Biol. 130:123-134.
Zorner, P. S., R. L. Zimdahl and E. E. Schweizer. 1984. Sources of viable seed loss in buried dormant and non-dormant populations of wild oat (Avena fatua) seed in Colorado. Weed Research 24: 143-150.
61 CHAPTER 4
MANAGEMENT OF COMMON GROUNDSEL (SENESCIO VULGARIS) IN
NEWLY ESTABLISHED STRAWBERRY
ABSTRACT
Common groundsel (Senecio vulgaris) is an increasingly important weed in strawberries, a crop in which open space within and between rows is susceptible to infestations.
Cultivation, hand hoeing, and registered herbicide are only partially effective in controlling common groundsel, and tolerance or resistance to herbicides is common in this species. Field and greenhouse studies were conducted to identify and select herbicides for controlling common groundsel in newly planted strawberries. Herbicides applied to strawberries within one week after planting in 2000 were: terbacil and simazine alone and tank mixed with napropamide; pendimethalin, dimethenamid, S- metolachlor, ethofumesate and sulfentrazone. Based on selectivity and efficacy observed in this preliminary experiment, sulfentrazone and flumiclorac were selected for further evaluation in 2001 and 2002. Strawberry tolerance of sulfentrazone and flumiclorac 1, 3,
6, and 18 weeks after application (WAA) was similar to that of the registered herbicides terbacil and napropamide, but injury was greater than in hand weeded plots. Plants sprayed with 300 g ai/ha sulfentrazone produced yields similar to terbacil treated plants, but with less plant stunting. Tolerance of newly planted ‘Allstar’ and ‘Jewel’ cultivars 62 was affected by the interaction of soil pH and sulfentrazone rate. Plant stunting 3 WAA increased with sulfentrazone rate, reaching 68 and 61% in ‘Allstar’ and ‘Jewel’, respectively, with the highest rate (400 g/ha) and high soil pH (7). ‘Allstar’ grown in low pH (5) and treated with sulfentrazone (400 g/ha) showed only 8% stunting, whereas
‘Jewel’ was not stunted 3 WAA at the same rate and pH. Both cultivars recovered from the severe injury observed when sulfentrazone was applied to high pH soils. However, at low pH both cultivars were stunted more at 6 WAA than at 3 WAA. Plant diameter for both cultivars was 25% higher when they were grown in the lower soil pH. Fruit yield was not affected by the sulfentrazone rates evaluated (0 to 400 g/ha). Sulfentrazone was active at four stages of common groundsel growth: preemergence (PRE), cotyledon
(COT), early post (EPOST) seedlings at the 4-leaf stage, and late post (LPOST) seedlings at the10 leaf stage. The calculated GR50 (g ai/ha) value for PRE and COT stages was 50, whereas the GR50 for EPOST and LPOST stages was 100. Sulfentrazone controlled common groundsel when applied PRE and COT, but at EPOST and LPOST stages sulfentrazone did not provide complete control, although plant height was reduced 80 to
90% compared to untreated plants. Results indicated that common groundsel is controlled in the field with 0.15 and 0.3 kg/ha of sulfentrazone applied before seedling emergence.
The least strawberry injury occurred when sulfentrazone was applied immediately after transplanting at 0.15 and 0.3 kg/ha, although crop tolerance was reduced under conditions of high soil pH (>6.5) and varied with cultivar.
63 INTRODUCTION
For strawberry growers using the matted row production system, weed competition during the first year of plant establishment is a major problem. Uncontrolled growth of weeds during the establishment year can reduce strawberry yield 90 % (Pritts and Kelly 2001). One month of competition following planting reduced yield 20%, and 2 months of competition reduced yield 65%. Soil fumigants, herbicides, cultivation, and weeding by hand are used by most growers to control annual weeds (Funt et al. 1985).
Methyl bromide (bromomethane) is applied on roughly half of the strawberry acreage in the U.S. and is especially critical in the raised-bed plasticulture system used on the majority of farms (Poling 1993). Fumigants have played a major role in achieving increased yields (USDA 2001); however, methyl bromide is to be phased out by 2005, creating a major gap in weed control and pest management (UNEP 2000) for many growers. Herbicides are applied to only 39 percent of the strawberry acreage in the U.S.
The main products applied are paraquat (1,1'-dimethyl-4,4'-bipyridinium ion) and napropamide (N,N-diethyl-2-(1-naphthalenyloxy) propanamide), which are used on 19% and 13% percent of the total area (respectively), followed by simazine (6-chloro-N,N- diethyl-1,3,5-triazine-2,4-diamine) and terbacil (5-chloro-3-(1,1-dimethylethyl)-6- methyl-2,4(1H,3H)-pyrimidinedione), with 6% each (USDA 2001).
Common groundsel is one of the most frequent species encountered in strawberries (MAFF-UK 1977; Clay 1985). Common groundsel is a prolific seeder and is self-pollinated (Haskell 1953). Its airborne seeds have an obligate light requirement for germination but otherwise exhibit little seed dormancy. Common groundsel produces
64 multiple life cycles per year, allowing seeds to increase rapidly in the soil seed bank
(Cussans 1966; Nielsen and Pinnerup 1982). The open space within and between strawberry rows provides an excellent niche for the establishment of this species.
Cultivation, hand hoeing and applications of registered herbicide are only partially effective in controlling common groundsel. Terbacil and simazine (at 150 g/ha) alone or tank mixed with napropamide (4.0 kg/ha), provided less than 60% control (Figueroa et al.
2002), although common groundsel is listed as a sensitive species on the label of napropamide. Resistance to terbacil and simazine has been reported in this species (Ryan
1970; Radosevich and Appleby 1973; Radosevich and Devilliers 1976; Vekshin et al.
1978; Ferriere 1986; Bouverat Bernier and Gallotte 1989; Netland et al. 1996; Mallory
Smith 1998), and may be a factor in the poor control observed with terbacil in our preliminary research.
Several herbicides have recently been identified by the IR-4 Program
(Anonymous 2003) as potentially useful on strawberry, including sulfentrazone (N-[2,4- dichloro-5-[4-(difluoromethyl)-4,5-dihydro-3-methyl-5-oxo-1H-1,2,4-triazol-1-yl-
]phenyl]methanesulfonamide), flumioxazin, pendimethalin, and s-metholachlor. This research was conducted to confirm selectivity of these and additional herbicides on strawberry and their efficacy on common groundsel in order to integrate the most promising product(s) into strawberry weed management recommendations.
65 MATERIALS AND METHODS
Herbicide efficacy studies
Crop tolerance and herbicide performance were evaluated during 2000, 2001, and
2002 on a strawberry farm near Wooster, Ohio (81°58’ W longitude, 40°45’ N latitude, elevation 310 m). The soil type was a Wooster silt loam (Oxyaquic Fragiudalf) with organic matter of 2.6, 1.0, and 2.8% and pH values of 5.5, 5.8 and 6.0, fro the three years, respectively. Wheat was harvested from all fields in July, followed by methyl bromide
(67%) fumigation at a rate of 393 kg/ha in September of the year before planting. Soil preparation consisted of chisel plowing and disking followed by two passes with a field cultivator in May. ‘Jewel’ strawberry plants4 were established a matted row, perennial production system with spacings of 45 cm within rows and 96 cm between rows. Five cultivations and two hand-hoe weedings were carried out during the summer, two or three weeks apart. Fertilizer was applied at a rate of 336 kg/ha (N:P:K= 9:23:30) before planting plus a top dressing of N at 33 kg/ha during the first summer. For the fruiting year, N (90 kg/ha) was added after plant renovation in July. All fields were irrigated as needed using a 60 by 60-solid set sprinkler irrigation system (2.5 to 3 mm/hour). Flower buds were removed during the establishment year within three to four weeks after planting.
Herbicides were applied within a week of planting, at the end of May each year.
Treatments were applied with a CO2-pressurized (276 kPa) backpack sprayer equipped with flat fan TJ-8002VS nozzles delivering a water volume of 187 L/ha. All treatments
4 Nourse Farms, 41 River Rd. South Deerfield, MA 01373, USA. 66 were replicated four times in a randomized complete block design. Plots (5 x 2 m) consisted of two rows with 10 plants per row. Rows were sprayed with a 2-m wide boom.
The treated area extended 50 cm beyond the outside edge of each strawberry row. At the time of herbicide application strawberry plants were actively growing and had 2 or 3 new leaves. Weeds had not emerged. Untreated control plots (hand weeded) were included in all the experiments.
A preliminary experiment carried out during 2000 included the herbicides most commonly used in strawberries in the Midwest: terbacil and simazine (both at 0.075 and
0.15 kg ai/ha) alone and tank mixed with napropamide at (4.0 kg ai/ha). Other herbicides included those identified through a database search of the literature as those that might have potential for use in strawberries: pendimethalin (N-(1-ethylpropyl)-3,4-dimethyl-
2,6-dinitrobenzenamine) and s-metolachlor (2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2- methoxy-1-methylethyl) acetamide) both at 1.75 and 3.5 kg ai/ha, dimethenamid ((RS) 2- chloro-N(2,4-dimethyl-3-thienyl)-N-(2-methoxy-1-methylethyl)acetamide) at 1.25 and
2.5 kg ai/ha, ethofumesate((±)-2-ethoxy-2,3-dihydro-3,3-dimethyl-5-benzofuranyl methanesulfonate) at 0.9 kg ai/ha and sulfentrazone (N-[2,4-dichloro-5-[4-
(difluoromethyl)-4,5-dihydro-3-methyl-5-oxo-1H-1,2,4-triazol-1-yl-
]phenyl]methanesulfonamide) at 0.42 kg ai/ha. These treatments were evaluated visually
3 weeks after application (WAA). Foliar injury was evaluated, using a scale of 0 to 5, in which 0=no damage, 1=leaf chlorosis <50%, 2=leaf chlorosis >50% and petioles twisting, 3=leaf chlorosis >50% and slight leaf necrosis restricted to the margins,
4=severe leaf necrosis, and 5=plant death. Strawberry plant stunting and common
67 groundsel control were also estimated, using a linear scale of 0 to 100, in which 0=no strawberry stunting or no common groundsel control and 100=complete stunting and complete control of groundsel. The data were used as a guide to design subsequent trials.
In 2001/02, only three herbicides showing low phytotoxicity in 2000 (<0.5% foliar injury and <12% plant stunting 3 WAA) or acceptable activity on groundsel
(>80%) were assessed further: terbacil, napropamide and sulfentrazone. Flumiclorac was also evaluated (0.033 and 0.045 kg ai/ha) based upon its prioritization by the IR4
Program as a herbicide with potential utility on strawberry. Crop tolerance was evaluated
1 and 3 WAA by visually estimating the percent plant stunting and chlorosis, where 0=no visible damage and 100=death of strawberry plants. Six WAA stolons were counted from the 5 central plants in each plot and the diameter of the crop canopy was measured as described by Manning and Fennimore (2001). At 18 WAA crop tolerance was reassessed, by measuring plant height and percent of ground covered by the strawberry canopy.
Percent groundsel control was also estimated at this time. In June 2002 and 2003, berries were harvested by hand on three dates from plants in the central 1-m of a randomly selected row in each plot. Fully red and ripened fruits were classified as marketable, and partially red or rotten fruits as unmarketable.
All data were subjected to the SAS GLM procedure using the repeated measurements statement for multiple evaluations of plant stunting and chlorosis within years. Means were separated by Fisher’s protected LSD at P = 0.05 or, when more sensitivity to potential crop damage was needed, at P=0.1. Percentage data were arcsine transformed when ANOVA assumptions were not fulfilled. Only non-transformed values
68 are presented. Data were combined across years if no year effect or treatment by year interactions occurred.
Effect of soil pH on strawberry tolerance to sulfentrazone
Our preliminary experiments indicated that strawberry tolerated sulfentrazone; however, Grey et al. (1997 and 2000) reported greater water solubility and mobility of sulfentrazone in soils with pH > 6.5, and increased availability for uptake by plants. Our herbicide studies were conducted in soils with pH ranging from 5.5 to 6; therefore, we speculated that crop tolerance might be reduced in soils of higher pH. To test this hypothesis, field studies were established at the Ohio Agricultural Research and
Development Center at Wooster during 2002 to determine the influence of soil pH on strawberry tolerance. Three factors (2 pH levels, 2 cultivars, and 4 sulfentrazone rates) were evaluated in a randomized complete block design with four replications per treatment. To obtain high pH plots, a 1:2 mix of medium textured silica sand (0.25–0.5 mm) and hydrated lime (Ca(OH)2) was added to the soil one week before planting in May
2002. A drop spreader was calibrated to apply a rate of 1 ton/ha (MSU-Extension 1995).
Analysis of soil samples taken 2 months after adding lime confirmed that soil pH had increased from 6.0 to 6.9. The increase in soil pH [7.0 ± 0.2 (CV=0.04 %)] was confirmed in every plot 5 months after adding lime. An immediately adjacent field with a soil pH of 5 was used for the low pH field. Strawberry cultivars5 ‘Jewel’ and ‘Allstar’ were planted in each main plot during May 2002. Two rows of each cultivar were
5 Nourse Farms, 41 River Rd. South Deerfield, MA 01373, USA.
69 assigned at random to four of eight sulfentrazone treated plots within each block. Each plot contained two rows of strawberry with 10 plants each. Nutrients were applied after planting (N at 40 kg/ha) and early fall (September) as potassium nitrate. Sulfentrazone was applied at 0, 0.1, 0.2, and 0.4 kg/ha one week after planting (WAP). All plots were hand weeded every other week. Irrigation was provided through central pivots, as needed during the summer. Methods previously described were used for estimating percent stunting and chlorosis, number of stolons, plant height and diameter (3 and 6 WAA) and fruit harvest.
ANOVA of data was carried out using SAS GLM procedures testing for significance of main effect and interactions. Because it was not possible to randomly replicate the pH effect, inferences to pH are limited. When significant differences occurred orthogonal contrasts were used for mean separation at the 5% significance level.
Sulfentrazone dose response
A greenhouse experiment was performed to determine the response of common groundsel at various growth stages to a range of sulfentrazone rates. On April 17, 2003 common groundsel was seeded in 110 mm plastic pots containing a Promix BX6 that consisted of: Canadian sphagnum peat moss (75-85% volume), perlite, vermiculite, dolomitic and calcitic limestone and a wetting agent. Seeded pots were placed in a greenhouse mist room (25 ± 1 °C) set to mist every 10 min for 10 s intervals. Plants were watered as needed and fertilized once a week with 200 ppm of a 20:20:20 (N:P:K)
6 Premier Horticulture Inc., Red Hill, PA, 18076.
70 solution. Seeds were planted four times, 10 days apart, to achieve four common groundsel seedling stages at herbicide application: PRE (preemergence), COT (cotyledon stage), EPOST (early post seedlings with 4 fully expanded leaves) and LPOST (late post seedlings with 10 fully expanded leaves). After one week in the mist room, plants were moved outdoors to benches under direct sun light to promote plant hardening and leaf cuticle development. The shortest interval between moving seedlings outside and herbicide application was 1 week for plants at COT.
A split plot design was used, with groundsel seedling stages as the main plot and sulfentrazone rate (0, 0.25, 0.50, 0.1, 0.2 and 0.4 kg/ha) as the subplot. Four replications were used. All groundsel seedling stages were sprayed at the same time. A compressed- air laboratory sprayer equipped with TJ-8003VS flat fan nozzles calibrated to deliver 187
L/ha at a pressure of 276 kPa was used. Groundsel response to sulfentrazone was estimated by measuring plant height 3 WAA. The experiment was repeated.
ANOVA was conducted using SAS GLM procedure, including analysis of interactions between main factors (groundsel seedling stages, sulfentrazone rates and experiment replication). Seedling height 3 WAA of all sulfentrazone treated groundsel plants was converted to percent of the untreated control. Each groundsel seedling stage was regressed on sulfentrazone rate using the SAS NLIN procedure. This procedure produced the parameters needed to fit a log-logistic function (Seedfeldt et al. 1995) and obtain the rate-response curves defined by the equation:
b % of control height = C + (D - C) /( 1 + (x/GR50) ) [1]
71 Where C = the mean response of the highest dose; D = mean response of the untreated; b
= slope; x= sulfentrazone rate; and GR50 = 50% growth reduction.
RESULTS AND DISCUSSION
Herbicides efficacy studies
Strawberry plants tolerated, or were only slightly injured, by 11 of 16 herbicides evaluated in 2000 (Table 4.1). Three WAA the size of strawberry plants in plots treated with terbacil, simazine, dimethenamid, s-metolachlor and sulfentrazone was similar to plants in the untreated control. Strawberry plants in plots treated with napropamide (4.0 kg/ha) tank-mixed with either terbacil (0.075 kg/ha) or simazine (0.15 kg/ha), pendimethalin, and ethofumesate were stunted. Pendimethalin caused severe stunting
(>20 %) and foliar injury (3.3). Strawberry foliar injury was also significant in plots treated with simazine (0.15 kg/ha), s-metolachlor (3.5 kg/ha), ethofumesate, and sulfentrazone. However, with the exception of ethofumesate and s-metolachlor at 3.5 kg/ha, plants in these plots were not injured as much as those in plots treated with pendimethalin.
Every herbicide treatment provided some control of common groundsel (Table
4.1). Treatments containing napropamide, the only herbicide recommended for control of the species, provided 38 to 70% control 3 WAA. Treatments of terbacil tank-mixed with napropamide were not better than terbacil alone. Napropamide did improve common groundsel control when used in combination with simazine at 0.075 kg/ha compared to this rate of simazine alone. Pendimethalin and dimethenamid controlled 63 and 76% of
72 common groundsel at the highest rates applied, 3.5 and 2.5 kg/ha, respectively. Common groundsel control increased from 43 to 78% when the rate of s-metolachlor was increased from 1.75 to 3.5 kg/ha. The best common groundsel control (100%) was achieved only in plots sprayed with sulfentrazone at 0.42 kg/ha. Because sulfentrazone provided excellent control of common groundsel and caused minimal crop stunting 3 WAA (<12%) with rapid recovery, it was selected as the most promising treatment for subsequent trials.
Fruits were not harvested from this study because a late season storm caused severe soil erosion that created gullies running through the plots.
Strawberry and common groundsel response to herbicides tested in 2001 and in
2002 did not differ between years; therefore, data presented are the average values after data were combined from both growing seasons (Table 4.2). One WAA, chlorosis was observed on strawberry plants treated with herbicides; however, this was only significant in plots treated with terbacil at 0.15 and terbacil 0.3 tank-mixed with napropamide.
Chlorosis in herbicide treated plots declined rapidly and by 3 WAA was no longer significant (data not reported). Stunting of herbicide treated strawberry plants was readily apparent 1 WAA, ranging from 13 % with sulfentrazone at 0.15 kg/ha and with terbacil tank-mixed with napropamide (0.15 + 4.0 kg/ha) to 34% with terbacil applied alone at 0.3 kg/ha. Plants treated with terbacil at 0.15 kg/ha remained severely stunted 3WAA. These data suggest a safening effect when napropamide was tank-mixed with terbacil. We have also observed this effect in other studies (Figueroa 2003). The high rate of sulfentrazone stunted strawberry plants at 1 and 3 WAA, but by 6 WAA stunting was no longer detected for this, or any other treatment, except for flumiclorac. Similarly, Manning and
73 Fennimore (2001) concluded that sulfentrazone (0.28 kg/ha) was safe for use immediately after transplanting newly established ‘Selva’ and ‘Camarosa’ strawberries.
Flumiclorac severely stunted strawberry plants at both rates and stunting persisted beyond 3 WAA.
Strawberry stolons, plant diameter, height and canopy cover measured at 6 and 18
WAA were not affected by herbicide treatments (data not reported). Failure to determine significant differences within these parameters at 6 WAA suggests that visual estimation of stunting was a more sensitive and reliable indicator of persistent crop injury.
Strawberry growth was greatest in plots sprayed with terbacil plus napropamide (0.3 + 4 kg/ha) and lowest in plots sprayed with terbacil alone (0.15 kg/ha). Fruit yield was significantly reduced in plots treated with terbacil at 0.15 kg/ha compared to yield in plots treated with the tank-mix of terbacil plus napropamide (0.3 +4.0 kg/ha). With the exception of terbacil at 0.15 kg/ha, fruit yield and quality in herbicide treated plots was similar to the untreated control.
Few weeds occurred in trials established in 2001 and 2002 during spring and summer of the first year because the fields had been fumigated with methyl bromide the fall prior to planting. Thus, observations on common groundsel control were delayed until late in the growing season (18 WAA), by which time seedlings had emerged in the plots.
Sulfentrazone at 0.15 and 0.3 kg/ha, and terbacil at 0.15 or 0.3 kg/ha tank-mixed with napropamide at 4.0 kg/ha produced high levels of common groundsel control (80% or greater), statistically equivalent to control in hand weeded plots (Figure 4.1). Terbacil at
0.15 kg/ha and flumiclorac at 0.03 and 0.05 kg/ha provided 50 to 60 % control.
74 Soil pH effects
Strawberry tolerance to sulfentrazone applied immediately after planting was affected by soil pH (Table 4.3). Strawberry plants were stunted more at soil pH 7 than at pH 5. ‘Jewel’ was relatively insensitive to sulfentrazone. Plant stunting at soil pH 5 was only detected at the highest rate (0.4 kg/ha) 6 WAA. Visual estimates of stunting indicated that ‘Jewel’ tolerance 3 WAA was reduced at soil pH 7; however, the cultivar had recovered 6 WAA except for those plots treated with sulfentrazone at 0.4 kg/ha.
‘Allstar’ was more sensitive to sulfentrazone than was ‘Jewel’ and recovered more slowly. At soil pH 5, 8% stunting was observed 3 WAA with 0.4 kg/ha, and by 6 WAA stunting was obvious at each rate of the herbicide. ‘Allstar’ was severely stunted by sulfentrazone at soil pH 7, 3 WAA. Six WAA some recovery had occurred but stunting was still apparent at 0.2 and 0.4 kg/ha. Fruit yield was not affected (p= 0.2194) by sulfentrazone at the rates evaluated (0 to 400 g/ha). These results are consistent with those of Wehtje et al. (1997) and Grichar et al. (2003) who reported improved control of
Cyperus spp. with sulfentrazone when soil pH was greater than 6.6. Improvements in weed control and greater crop sensitivity may both be attributed to increased sulfentrazone availability in solution for absorption by plants at soil pH > 6.6 (Grey et al.
1997).
Measures of strawberry plant diameter were not sensitive to differential stunting caused by sulfentrazone rate and soil pH (Table 4.3). Plant diameter did not vary within a cultivar across rates of sulfentrazone at 3 or 6 WAA. However, measurement of this variable at 6 WAA illustrated the greater plant size achieved by ‘Jewel’ compared to ‘Allstar’ and
75 the enhanced growth of both cultivars at pH 5 compared to pH 7. These data suggest that visual estimates provide a better integration of the variables involved in the strawberry plant’s response to sulfentrazone than do the individual quantitative measures of plant growth used in this study.
Sulfentrazone dose response
Common groundsel seedling growth stage at the time of sulfentrazone application influenced subsequent plant growth (Figure 4.2). Common groundsel was very sensitive at the PRE and COT stages of growth. Later stages of growth were less sensitive, with
LPOST seedlings being slightly more sensitive than EPOST. Common groundsel was completely controlled when sulfentrazone was applied PRE at 0.025 kg/ha, and at 0.05 kg/ha to seedlings at the COT stage. Seedlings sprayed with sulfentrazone at EPOST and
LPOST responded in a curvilinear fashion to rates between 0 and 0.2 kg/ha. At 0.4 kg/ha
EPOST and LPOST seedlings did not die, but achieved only 20% of the height of untreated plants. These data indicate that sulfentrazone applications should be timed to coincide with groundsel emergence to achieve optimum control. Strawberry growers in
Ohio who have used this herbicide under a Section18 registration have confirmed this observation. Later applications of sulfentrazone corresponding with the EPOST and
LPOST timings used in this study are unlikely to provide complete control, but will likely minimize common groundsel growth and reproduction.
Our results show that common groundsel is readily controlled in the field with applications of sulfentrazone at 0.15 and 0.3 kg/ha applied in advance of seedling emergence. Lower rates of the herbicide, 0.025 and 0.05 kg/ha respectively, controlled 76 groundsel growing in pots when applied at PRE and at COT stages of growth and may prove effective in future research under field conditions. Later stages of common groundsel seedling growth, EPOST (4-leaf stage) and LPOST (10-leaf stage), were severely injured and subsequent growth suppressed when sulfentrazone was applied to potted plants at 0.1 to 0.4 kg/ha. This result is in agreement with growers who have observed less than complete control when sulfrentrazone was applied to strawberry in late fall, after common groundsel seedling establishment. Strawberry tolerance of sulfentrazone applied immediately after transplanting at 0.15 and 0.3 kg/ha was comparable to that with terbacil, a standard herbicide used for many years. However, we found that tolerance was reduced under conditions of high soil pH(>6.5) and varied with cultivar.
77
Groundsel Herbicide treatment Rate Foliar injurya Crop stunting control kg ai/ha ______% ______Control --- 0 0 0 Terbacil 0.075 0.1 9 53 Terbacil 0.15 0.4 9 45 Simazine 0.075 0.3 6 46 Simazine 0.15 1.0 11 63 Terbacil + Napropamide 0.075 + 4.0 0.5 12 38 Terbacil + Napropamide 0.15 + 4.0 0.1 8 58 Simazine + Napropamide 0.075 + 4.0 0.4 9 70 Simazine + Napropamide 0.15 + 4.0 0.8 16 65 Pendimethalin 1.75 2.3 23 64 Pendimethalin 3.5 3.3 33 76 Dimethenamid 1.25 0.6 5 50 Dimethenamid 2.5 0.5 6 63 S-Metolachlor 1.75 0.8 6 43 S-Metolachlor 3.5 1.6 9 78 Ethofumesate 0.9 1.5 12 64 Sulfentrazone 0.42 1.2 11 100 LSD (P=0.05) 1 12 26
Table 4.1: Strawberry injury and common groundsel control 3 weeks after application (WAA) in response to herbicides applied the day of transplanting in 2000. Foliar injury index: 0= no damage; 1= leaf chlorosis <50%; 2= leaf chlorosis >50% and petioles twisting; 3= leaf chlorosis >50% and slight leaf necrosis restricted to the margin; 4= severe leaf necrosis, and 5= plant death.
78
Chlorosis Stunting Fruit yield Herbicide Rate 1 WAA 1 WAA 3 WAA kg ai/ha ______% ______kg/m2 Control --- 0 0 0 2.46 Terbacil 0.15 14 34 27 2.33 Terbacil + Napropamide 0.15 + 4.0 5 13 8 2.67 Terbacil + Napropamide 0.30 + 4.0 17 20 17 2.88 Sulfentrazone 0.15 5 13 14 2.41 Sulfentrazone 0.30 8 20 20 2.61 Flumiclorac 0.033 3 19 17 2.54 Flumiclorac 0.045 13 30 18 2.63 LSD* (P=0.1) 14 18 13 0.5
Table 4.2: Response of newly planted strawberry at 1 and 3 weeks after application (WAA) to herbicides applied immediately after transplanting. Combined for 2001 and 2002. * P= 0.1 was used to reduce risk of type II error and to make analysis more sensitive to potential damage.
79
Cultivar Sulfentrazone Plant stunting rate 3 WAA 6 WAA PH5 pH7 pH5 pH7 kg/ha _____ % _____ Pr > F _____ % _____ Pr > F Allstar 0 0 0 NS 0 0 NS 0.1 5 25 * 11 13 NS 0.2 3 38 ** 11 25 * 0.4 8 68 *** 23 50 **
Jewel 0 0 0 NS 0 0 NS 0.1 0 11 NS 5 8 NS 0.2 1 30 ** 5 13 NS 0.4 3 61 *** 18 25 NS
LSD 6 28 6 20 (P=0.05)
Table 4.3: The response of Allstar and Jewel strawberry cultivars to sulfentrazone rates and soil pH levels at 3 and 6 weeks after application (WAA) in 2002. NS= no significantly different; * = p ≤ 0.05; ** = p ≤ 0.01; *** = p ≤ 0.0001
80 100 Terbacil Terbacil+Napropamide Sulfentrazone 80 Flumioxazin
LSD
60
% Control 40
20
0 0.15 0.15+4 0.3+4 0.15 0.3 0.03 0.05 kg/ha
Figure 4.1: Control of common groundsel in 2001 and 2002 at 18 WAA of herbicide treatments to newly transplanted strawberry plants. Error bar represent the LSD (P = 0.05) to compare treatment response combined by years.
81 100 GROUNDSEL PRE COT EPOST LPOST 80
60
40
20 Groundsel Height, % of Untreated
0
0 50 100 150 200 250 300 350 400 Rate (kg/ha)
Figure 4.2: The effect of common groundsel growth stage and rate of sulfentrazone on common groundsel height 3 weeks after application (WAA). Nonlinear regression (solid symbols) and raw means (outline symbols) were plotted with means combined over experiments for plant height at 3 WAA as a percentage of the untreated control. Stages of common groundsel growth were: preemergence (PRE), cotyledon (COT) = seedlings at the cotyledon stage, early post (EPOST) = seedlings at the 4 leaf stage and late post (LPOST) = seedlings at the 10 leaf stage.
82 LITERATURE CITED
Anonymous 2003. Food used workshop. Orlando, Florida, IR4 Project: 29-30.
Bouverat Bernier, J. P. and P. Gallotte. 1989. Chemical weed control in peppermint post- planting. Herba Gallica 1: 33-37.
Clay, D. V. 1985. Appendix - results of a questionnaire on the worst weeds in vine and soft fruits. Proceedings of a meeting of the EC Experts' Group, Dublin: 157-160.
Cussans, G. 1966. The weed problem. Proceedings 8th British Weed Control Conference.
Ferriere, I. 1986. Resistance phenomena in all areas. Cultivar No.92: Supplement, 6-8.
Figueroa, R. 2003. Biology and management of common groundsel (Senecio vulgaris L) in strawberries. Horticulture and Crop Science. Wooster, Ohio, The Ohio State University.
Figueroa, R., D. J. Doohan and J. Cardina. 2002. Efficacy and crop tolerance of sulfentrazone on strawberries. North Central Weed Science Society, St. Louis, Missouri, WSSA.
Funt, R. C., B. L. Goulart, C. K. Chandler, J. D. Utzinger, M. A. Ellis, R. M. Riedel, R. N. Williams and M. A. Palmer 1985. Ohio strawberry manual, The Ohio State University, Cooperative extension service: 43.
Grey, T. L., R. H. Walker, G. R. Wehtje and H. G. Hancock. 1997. Sulfentrazone adsorption and mobility as affected by soil and pH. Weed Science 45: 733-738.
Grey,T. L., Walker, R. H., Wehtje, G. R., Adams, J. Jr., Dayan, F. E., Weete, J. D., Hancock, H. G. and O. Kwon. 2000. Behavior of sulfentrazone in ionic exchange resins, electrophoresis gels, and cation-saturated soils. Weed-Science 48 (2): 239- 247.
83 Grichar, W. J., B. A. Besler and K. D. Brewer. 2003. Purple nutsedge control snd potato (Solanum tuberosum) toleranced to sulfentrazone and halosulfuron. Weed Technology 17: 485-490.
Haskell, G. 1953. Adaptation and the breeding system in groundsel. Genetica 26: 468- 484.
MAFF-UK.1977. Strawberry weed survey. In Review of Development Work 1976 South West Region. Her Majesty's Stationery Office: 83.
Mallory Smith, C. 1998. Bromoxynil-resistant common groundsel (Senecio vulgaris). Weed Technology 12 (2): 322-324.
Manning, G. R. and S. A. Fennimore. 2001. Evaluation of low-rate herbicides to supplement methyl bromide alternative fumigants to control weeds in strawberry. HortTechnology 11 (4): 603-609.
MSU-Extension . 1995. Tri-State fertilizer recommendations for corn, soybeans, wheat and alfalfa. East Lansing, MI, Michigan State, Ohio State and Purdue Universities: 21.
Netland, J., et al. 1996. Weed species and frequency of simazine-resistant populations of Poa annua and Senecio vulgaris in nursery stocks imported to Norway or inland- raised. Proceedings of the second international weed control congress Denmark: 25-28 June 1996: Volumes 1-4. 1996, 461-468.
Nielsen, H. and S. Pinnerup 1982. Reduced cultivation and weeds. Proceedings 23rd Swedish Weed Conference.
Poling, E. B. 1993. Strawberry plasticulture in North Carolina: II. Preplant, planting, and postplant considerations for growing 'Chandler' strawberry on black plastic mulch. HortTechnology 3 (4): 383-393.
Pritts, M. P. and M. J. Kelly. 2001. Early season weed competition reduces yield of newly planted matted row strawberries. HortScience 36 (4): 729-731. 84 Radosevich, S. R. and A. B. Appleby. 1973. Studies on the mechanism of resistance to simazine in common groundsel. Weed Science 21 (6): 497-500.
Radosevich, S. R. and O. T. Devilliers. 1976. Studies on the mechanism of s-triazine resistance in common groundsel. Weed Science 24 (2): 229-232.
Ryan, G. F. 1970. Resistance of common groundsel to simazine and atrazine. Weed Science 18(5): 614-616.
Seedfeldt, S., J. Jensen and P. Fuerst. 1995. Log-logistic analysis of herbicide dose- response relationships. Weed Technology 9: 218-227.
UNEP 2000. The Montreal Protocol on Substances that Deplete the Ozone Layer. Nairobi, Kenya, United Nations Environment Programme.
USDA 2001. Agricultural chemical usage, 2000 Vegetable summary, USDA-NASS. 2003.
Vekshin, B. S., B. Grigolava, G. P. Pushkina and N. V. Butina. 1978. Results of herbicide testing on plantations of mound lily (Yucca gloriosa) and herbaceous periwinkle (Vinca herbacea). Khimiko Farmatsevticheskii Zhurnal 12(4): 83-86.
Wehtje, G. R., R. H. Walker, T. L. Grey and H. G. Hancock. 1997. Response of purple (Cyperus rotundus) and yellow nutsedges (C. esculentus) to selective placement of sulfentrazone. Weed Science 45: 382-387.
85 CHAPTER 5
RESPONSE OF ESTABLISHED STRAWBERRY TO PREEMERGENCE AND
POSTEMERGENCE HERBICIDES
ABSTRACT
Field experiments were conducted during 2001 through 2003 in Wooster, OH to determine the strawberry plant response to clopyralid used after plant renovation in established plantings. Common groundsel control with clopyralid at 0.1 kg/ha was 63 and
79% at 3 and 6 weeks after treatment (WAT), respectively. Only a 12% increase in control was obtained with 400 g/ha at 6 WAT. Clopyralid rates significantly affected total fruit production. Maximum fruit yield was obtained from plots sprayed with clopyralid at
0.2 kg/ha. Lower yields were obtained with clopyralid at doses below and above 0.2 kg/ha. Late summer applications of clopyralid tended to reduce the canopy area of the strawberry crop, even when applied at 0.025 kg/ha, but this trend was not significant.
Overall, clopyralid applied POST at 0.2 kg/ha provided safe (no fruit yield reduction), as well as effective control of common groundsel if applied after strawberry renovation when common groundsel plants enter reproductive stages.
86 INTRODUCTION
In the perennial matted-row strawberry production system, controlling weeds is critical during fruiting years when cultivation, hand weeding, and herbicide applications are less effective than in the establishment year (Pritts and Kelly 2001). Vezina and
Bouchard (1989) reported that weed infestations delayed fruit maturation and decreased the yield at second harvest by as much as 50%. With the exception of 2,4-D amine (2,4- dichlorophenoxy acetic acid), no herbicides are available with activity on important weeds such as common groundsel (Senecio vulgaris L.), Canada thistle (Cirsium arvense
(L.) Scop.), dandelion (Taraxacum officinale Weber in Wiggers), and red sorrel (Rumex acetosella L.). Only a single application of 2,4-D is permitted, at post-harvest renovation.
Control of broadleaf weeds with 2,4-D is variable and most of the important weeds are not present at susceptible stages of growth at strawberry renovation.
Previous research by these authors and others (Wood 2003) suggests that clopyralid (3,6-dichloro-2-pyridinecarboxylic acid) is an effective alternative to 2,4-D in strawberry, providing superior weed control and crop safety. In the US, clopyralid is registered on wheat, barley, oats, field corn, tree plantations, and asparagus; it controls weeds in the Fabaceae, Asteraceae, Polygonacae, and Solanaceae families (Dow 2002).
Clopyralid herbicide is registered for use in strawberry in Canada, the UK and Germany, at a maximum rate of 0.125 kg ae/ha (Dow, personal communication). A single application of clopyralid at post-harvest renovation is permitted in Canada (Anonymous
1999). Treatments applied in the spring before strawberry bloom are recommended in the
UK for control of Canada thistle (Clay and Andrews 1984). Jensen (1986) reported that
87
clopyralid applied at strawberry post-harvest renovation provided a superior crop safety and better control of dandelion and Canada thistle than 2,4-D. Clopyralid selectivity on strawberry varied with crop age and herbicide dose (Clay and Andrews 1984). In 2003, a supplemental label permitting use of clopyralid on established strawberries was issued in
OH (Dow 2003).
In Ohio, common groundsel has increased in importance as a weed in strawberry fields during the past 10 years. Control is complicated by resistance to many herbicides
(Ryan 1970; Radosevich and Devilliers 1976; Fuerst 1984; Mallory Smith 1998; Beuret
1989). Figueroa et al (2002) found that common groundsel in Ohio strawberry fields was inadequately controlled by applications of napropamide alone or tank-mixed with terbacil, which helps explain the recent build up of this species in Ohio. Common groundsel is known to tolerate 2,4-D at rates recommended for use in strawberry
(Anonymous 1999); however, Doohan and Jensen (1997) reported excellent control of this weed with clopyralid at rates as low as 0.050 kg/ha.
The objective of this research was to confirm clopyralid efficacy on common groundsel, tolerance of established strawberries to the herbicide, and to provide data to support development of recommendations.
88
MATERIALS AND METHODS
Strawberry tolerance and response of common groundsel to clopyralid were evaluated at Wooster, Ohio (81°58’ W longitude, 40°45’ N latitude, elevation 310 m) from 2001 to 2003. The soil was a Wooster silt loam (Oxyaquic Fragiudalf) with soil organic matter of 2.8% and pH of 6.0. ‘Jewel’ strawberries, planted in May 1999 and
2001, were used for trials in 2001/02 and 2002/03, respectively. Nitrogen (ammonium nitrate) was applied at 90 kg/ha after harvest in July each year. All fields were irrigated as needed, using a 60 by 60-solid set sprinkler irrigation system that applied 2.5 to 3 mm of water /hour). Herbicides were applied with a CO2-pressurized sprayer with TJ-8002VS nozzles7 at 240 kPa and a water volume of 187 L/ha. Untreated control plots were weeded by hand. Prior to clopyralid application in September 2001 and 2002, common groundsel density was estimated to ensure homogeneity between plots. At application, common groundsel plants were entering reproductive stage (10% flowering), 25 cm in height. Plots were a single row of strawberries 3 m long. A completely random design was used with 4 replications per treatment.
Three and 6 WAT, common groundsel control was estimated visually (0 = no control and 100=complete cessation of growth). Flowering of surviving common groundsel plants was estimated 6 WAT. Crop tolerance was determined by measuring ground area covered by the crop 3 and 6 WAT. Height of four randomly selected strawberry plants was measured 3 WAT. Fruit yield was recorded in June 2002 and 2003,
7 Teejet extended range flat spray tip. Spraying Systems Co., PO Box 7900, Wheaton, IL 60189-7900, USA. 89
when berries were harvested by hand on three dates from plants in the central 1-m of each row. Ripe fruits were classified as marketable, and partially red or rotten fruits as unmarketable. Data were subjected to ANOVA using SAS MIXED procedure (SAS
2000). Means were separated using Fisher’s protected LSD test at P=0.05. Data were combined for both years after statistical analysis indicated no year effect on any of the variables evaluated or interaction between year and herbicide. The response of common groundsel to clopyralid dose was analyzed using a log-logistic equation developed with the SAS NLIN procedure for fitting non-linear regression functions (Seedfeldt et al.
1995):
% Control = C + D – C [1] b 1 + (x/I50)
where C = mean response of highest doses, D = mean response of untreated, b = slope, x= clopyralid dose and I50 = dose giving 50% response. We verified that the regression function described the data satisfactorily by performing a lack-of-fit F-test (Weisberg
1985). Percent common groundsel control was plotted against the response curves using
Sigma Plot 8.08 software.
8 Sigma Plot 2002 for Windows Version 8.0, SPSS Inc., 233 S. Wacker Drive, Chicago, IL 60606.
90
RESULTS AND DISCUSSION
Ground area covered by strawberry plants varied with the rate of clopyralid applied
(Table 5.1). Plants sprayed with clopyralid up to 0.2 gk/ha were similar in plant area to plants in hand weeded control plots 3 WAT and at 6 WAT reduction in plant area could only be detected when clopyralid was applied at the highest rate (0.4 kg/ha). Differences in height attributable to clopyralid could not be detected (data not reported).
Control of common groundsel increased proportionally to the clopyralid rate used over the range from 0.025 to 0.1 kg/ha, beyond which smaller improvements in control were achieved (Figure 5.1). Six WAT the lowest rate of clopyralid (0.025 kg/ha) suppressed groundsel (25%), but plants were not killed. Common groundsel control improved during the period from 3 to 6 WAT. Groundsel control with 100 g/ha was 63%
3 WAT and about 79% at 6 WAT. Almost complete control (91%) of common groundsel was obtained with 0.4 kg/ha, however this was only 12% higher than control with 0.1 kg/ha at 6 WAT. These data support recommendation of an effective rate of clopyralid for groundsel control rate of at least 0.1 kg/ha. Reduction in bloom increased linearly as the rate of clopyralid increased, and was completely inhibited in plants treated with 0.4 kg/ha. Even at 0.025 kg/ha of clopyralid, groundsel bloom was reduced by 43% (6
WAT). When the rate was increased to 0.05 kg of clopyralid, a third of the groundsel plants produced and released seeds. Regardless of clopyralid rate applied groundsel plants died before spring.
91
Clopyralid rates significantly affected total fruit production, conforming with differences observed the previous autumn in visual estimates of crop tolerance and common groundsel control. Maximum fruit yield (2.9 kg/plant) was obtained from plots sprayed with clopyralid at 0.2 kg/ha. Smaller yields ranging from 2.3 to 2.5 kg/plant were obtained from the hand weeded control and from plots treated with clopyralid rates of
0.025 to 0.100 kg/ha. Though groundsel plants were removed from hand weeded plots at the time of clopyralid application and at times of evaluation (3 and 6 WAT), additional groundsel seedlings emerged following each hand weeding. Competition from these seedlings may have contributed to the reduced yield in control plots. Likewise, lower yields obtained with clopyralid at 0.025 and 0.1 kg/ha provided inferior groundsel control relative to higher rates of the herbicide. Competition from these clopyralid suppressed groundsel plants may have been sufficient to suppress berry yield. Plants treated with clopyralid at 0.4 kg/ha produced the least fruit of all herbicide treated and hand-weeded plots, only 33% of the maximum fruit yield. Yield (Table 5.1) and number (data not reported) of unmarketable berries was not affected by clopyralid dose.
Late summer applications of clopyralid tended to reduce the canopy area of the strawberry crop, even when applied at 0.025 kg/ha but this trend was not significant.
Applications at 0.2 or 0.1 kg/ha provided acceptable control of common groundsel and largely prevented seed production. These rates did not suppress growth of strawberry foliage and increased berry yield. However, the maximum rate applied, 0.4 kg/ha significantly affected the crop canopy at 3 and 6 WAA and reduced yield. Common
92
groundsel was not adequately controlled at the lowest rates of clopyralid, 0.025 and 0.05 kg/ha. Ohio has recently been granted a Section 24C label for clopyralid use on strawberry after renovation. Registration of this use was supported in part by data produced through this research.
93
Crop area Fruit yield Treatment Rate 3 WAT 6 WAT Total Marketable Unmarketable kg m2 . kg / plant . ai/ha Hand --- 0.51 a 0.44 a 2.3 b 1.6 bc 0.7 a weeded Clopyralid 0.025 0.49 a 0.43 a 2.4 b 1.7 ab 0.7 a Clopyralid 0.050 0.47 a 0.38 a 2.4 b 1.6 bc 0.8 a Clopyralid 0.100 0.49 a 0.33 ab 2.5 b 1.6 a-c 0.9 a Clopyralid 0.200 0.45 ab 0.34 ab 2.9 a 2.0 a 0.9 a Clopyralid 0.400 0.39 b 0.30 b 2.0 c 1.3 c 0.7 a
Table 5.1: Strawberry foliage growth at 3 and 6 weeks after treatment (WAT) and yield response to clopyralid Data were combined for 2001and 2002 after ANOVA indicated no year effect or interaction between years with the herbicide treatments. Values for treatments within columns followed by the same letter are not significantly different according to Fisher’s protected LSD test (P≤ 0.1).
94
Height 3 WAT: Y=13.35+85.66/[1+(x/59.46)1.89] R2=0.93 Height 6 WAT: Y=7.23+93.27/[1+(x/39.77)1.79] R2=0.86 100 Flowering 6 WAT: Y=-0.73+100.93/[1+(x/29.91)1.36] R2=0.83
80
60
40 % of % of Untreated
20
0
0 0.025 0.05 0.1 0.2 0.4 Clopyralid rate (kg/ha)
Figure 5.1: Control of common groundsel with clopyralid applied postemergence to ‘Jewel’ strawberry (2001 and 2002). Regressions were combined over years. Y axis is common groundsel control, as % of growth (height) of the untreated control, at 3 and 6 weeks after treatment (WAT) and flowering at 6 WAT.
95
LITERATURE CITED
Anonymous 1999. Guide to weed control. Table 21: Classification of weeds according to response to various foliage sprays. Toronto, Ontario Ministry of Agriculture, Food and Rural Affairs. Queen's Printer for Ontario.: 277.
Beuret, E. 1989. A new problem of herbicide resistance: Senecio vulgaris L. in carrot crops treated with linuron. Revue Suisse de Viticulture, d'Arboriculture et d'Horticulture 21(6): 349-352.
Clay, D. V. and L. Andrews. 1984. The tolerance of strawberries to clopyralid: effect of crop age, herbicide dose and application date. Aspects of Applied Biology No.8: 151-158.
Doohan, D.J. and K.I.N. Jensen. 1997. Fine tuning weed management. Proc. North Am. Straw. Growers Assoc. 14: 31-36.
Dow. 2002. Stinger, specimen label, D02-043-012, Dow AgroSciences LLC. 2003.
Dow. 2003. Stinger, registration, OH-030004 D06-043-082 strawberry, Dow Agrosciences LLC. 2003.
Figueroa, R., D. J. Doohan and J. Cardina. 2002. Efficacy and crop tolerance of sulfentrazone on strawberries. North Central Weed Science Society, St. Louis, Missouri, WSSA.
Fuerst, E. P. 1984. Effects of inhibitors and diverters of photosynthetic electron transport on herbicide resistant and susceptible weed biotypes. Dissertation Abstracts International, B Sciences and Engineering 45 (4): 1079b-1080b.
96
Jensen, K. I. N. 1986. Response of Kent and Veestar strawberries to 2,4-D, dicamba and clopyralid. Annual Report, Research Station, Kentville, Nova Scotia: 19-20.
Mallory Smith, C. 1998. Bromoxynil-resistant common groundsel (Senecio vulgaris). Weed Technology 12(2): 322-324.
Pritts, M. P. and M. J. Kelly. 2001. Early season weed competition reduces yield of newly planted matted row strawberries. HortScience 36(4): 729-731.
Radosevich, S. R. and O. T. Devilliers. 1976. Studies on the mechanism of s-triazine resistance in common groundsel. Weed Science 24(2): 229-232.
Ryan, G. F. 1970. Resistance of common groundsel to simazine and atrazine. Weed Science 18(5): 614-616.
SAS. 2000. Statistical Analysis Systems User's Guide, version 8.1. Cary, NC, USA, SAS Institute Inc: 1686.
Seedfeldt, S., J. Jensen and P. Fuerst. 1995. Log-logistic analysis of herbicide dose- response relationships. Weed Technology 9: 218-227.
Vezina, L. and C. J. Bouchard. 1989. Competition with sheep's sorrel (Rumex acetosella L.) with cultivated strawberries. Naturaliste Canadien 116(4): 237-243.
Weisberg, S. 1985. Applied linear regression. New York, John Wiley & Sons: 96-97.
Wood, A. 2003. Compendium of pesticides common names (http://www.alanwood.net). 97 CHAPTER 6
SUMMARY AND CONCLUSIONS
Germination of common groundsel populations collected at 6 sites from Michigan to
Kentucky suggested that variability in germination corresponds to changes in latitude and climate. The initial experiment indicated that the germination response to temperature varied among plants from different environments and might be genetically controlled. However, different results were obtained when seeds from plants of each collection site were grown in a common environment. Germination was similar for seeds from each collection site across the temperature gradient (P value for sites ranged from 0.45-0.70 across the gradient).
Germination at 10 and 15 C remained very high, nearly 100%, and this response was also observed at 20 C. Percent germination of seeds from each collection site declined somewhat at 5 C, ranging from 60-80%. A trend towards reduced germination (80%) was noted in seeds of plants collected at New Carlisle and KY when they were incubated at 25 C; however, this was not significant. The second experiment suggested that the maternal environment has a strong impact on how F1 seeds behave in response to temperature.
Studies on the effect of temperature and day-length on germination suggest that the survival strategy for plants growing under summer conditions of warm, long days, was to produce tall plants capable of dispersing non-dormant seeds to distant sites in an effort to reach
98 suitable gaps that favor quick establishment of a second generation (Bergelson et al 1993).
This is in contrast to plants produced in autumn conditions of cool, short days, whose more abundant inflorescences yielded dormant seeds with little potential for distant dispersal.
These findings suggest that common groundsel plants alter their reproduction and dispersal strategy depending on growing conditions. Plants growing in autumn conditions favor dispersal in time by producing relatively more dormant seeds that can survive unfavorable conditions for germination. Plants growing in summer conditions favor dispersal in space by producing relatively fewer seeds that are non-dormant but have greater potential for dispersal to sites where conditions are right for rapid regeneration. Results of studies to detect the growth stage sensitive to thermal environment demonstrated several roles of temperature in modifying the germination of common groundsel. Even though seeds of this species have an obligate requirement for light to terminate dormancy so that germination can proceed (Hilton 1983), the dormancy level of seeds and consequent percent germination is modified by temperature in various ways. Temperature alters seed germination directly in the familiar germination response curve (Figure 2.2) with a broad optimum temperature for germination and decreasing germination at temperature extremes. Temperature also affected the germination response of seeds indirectly by altering the physiology of seeds produced on plants exposed to varying growth conditions. Maternal temperature conditions were more important than day-length in determining the physiological status of F1 seeds. Highly dormant seeds were produced in cool temperature conditions and non-dormant seeds were produced in warm conditions regardless of day-length. Temperature conditions of the maternal environment also altered the germination response of common groundsel seeds
99
from plants collected at Essexville (MI) and Lexington (KY) and later grown in constant and non-constant thermal environments. Plants in constant cold and warm environments produced seeds that were highly dormant and non-dormant, respectively, at maturity (Figure
2.5). Changing temperature conditions from warm to cold during reproductive development increased seed dormancy, especially the earlier the change in temperature occurred during development. However, the impact of moving plants from a cold to a warm environment depended on the source of the maternal plants (Michigan vs Kentucky) and the time during development that environmental conditions changed. The dominant role of temperature in determining germination behavior is typical of plants that function both as winter and spring annuals (Fenner 1991, Gutterman 2000). This adaptation allows common groundsel to alter its reproductive strategy depending on when seeds are produced, and is probably a critical factor that allows for multiple generations in a calendar year.
Seed dormancy was not observed initially after burial in late spring and early summer 2000, but increased over time reaching maximum dormancy at the end of winter
2001. At the beginning of spring, germination recovered to 60% indicating release of dormancy. Results from 2000-02 are similar to the study by Karssen (1980) where seeds buried in November increased in dormancy with elevated temperatures. Germination declined to less than 10% by the end of March 2002 at which time achenes appeared empty and light in color indicating death. This seed mortality was probably due to germination of buried seeds, followed by death of seedlings before emergence, as has been documented in various species (Baskin and Baskin 1998). A similar pattern was
100
observed in the seeds buried in 2002, but with a narrower range of germination.
Dormancy was not detected soon after burial but increased during fall as reflected by decreased germination throughout that season. A slight increase in germination at the end of winter 2003 indicated release from dormancy. During spring 2003 the slope of seed germination became more negative, reaching a plateau of approximately 60% during the summer months. Data indicated that common groundsel follows a cycle of dormancy and non-dormancy in-step with decreases and increases, respectively, in soil temperature.
The general pattern corresponds with that of winter annuals in which seasonal cycles of warm and cold soil temperatures, respectively break and induce seed dormancy (Baskin and Baskin 1998). Virtually all buried seeds germinated or otherwise died during two years of deep burial in undisturbed soil. Data from seedling emergence studies and artificial seedbank experiments indicate that common groundsel seeds may not persist in significant numbers beyond a few months in regularly disturbed soils. Infrequent rainfall and high soil temperatures (>25 C) may enforce dormancy somewhat, possibly extending the life of the seed bank especially in soils that are rarely disturbed. These results indicate that eradication of common groundsel from the seedbank might be done with shallow tillage and moderate irrigation when necessary to stimulate emergence.
However, additional studies should be conducted with seeds ripened under cool conditions of fall and winter to document similar or different physiology.
Sulfentrazone controlled common groundsel when applied PRE and COT, but at
EPOST and LPOST stages sulfentrazone did not provide complete control, although plant
101
height was reduced 80 to 90% compared to untreated plants. Results indicated that common groundsel is controlled in the field with 0.15 and 0.3 kg/ha of sulfentrazone applied before seedling emergence. The least strawberry injury occurred when sulfentrazone was applied immediately after transplanting at 0.15 and 0.3 kg/ha, although crop tolerance was reduced under conditions of high soil pH (>6.5) and varied with cultivar.
Late summer applications of clopyralid tended to reduce the canopy area of the strawberry crop, even when applied at 0.025 kg/ha but this trend was not significant.
Applications at 0.2 or 0.1 kg/ha provided acceptable control of common groundsel and largely prevented seed production. These rates did not suppress growth of strawberry foliage and increased berry yield. However, the maximum rate applied, 0.4 kg/ha significantly affected the crop canopy at 3 and 6 WAA and reduced yield. Common groundsel was not adequately controlled at the lowest rates of clopyralid, 0.025 and 0.05 kg/ha.
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APPENDICES
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APPENDIX A GROWTH RESPONSE OF ANNUAL WEED SPECIES TO SULFENTRAZONE DOSE
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100 CHICKWEEDGROUNDSEL PRE COT EPOST LPOST 80
60
40 Height, % of untreated Height, Height, % of untreated 20
0
0 50 100 150 200 250 300 350 400
Rate (kgRate ai/ha) (kg ai/ha)
Figure A.1: Response (plant height) of four stages of common chickweed (Stellaria media (L.) Vill) growth to sulfentrazone. Nonlinear regression (full symbols) and raw means (empty symbols) are plotted with means combined over experiments for plant height at 21 d after treatment as a percentage of the untreated control. Stages of growth were: preemergence (PRE), cotyledon (COT) with seedlings at the cotyledon stage, early post (EPOST) with seedlings at the 4 fully expanded leaf stage and late post (LPOST) with seedlings at the 10 leaf stage.
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100 LAMBSQUARTER PRE COT EPOST LPOST 80
60
40 Height, % of untreatedHeight, 20
0
0 50 100 150 200 250 300 350 400 Rate (kg ai/ha)
Figure A.2: Response (plant height) of four stages of common lambsquarter (Chenopodium album L.) growth to sulfentrazone. Nonlinear regression (full symbols) and raw means (empty symbols) are plotted with means combined over experiments for plant height at 21 d after treatment as a percentage of the untreated control. Stages of growth were: preemergence (PRE), cotyledon (COT) with seedlings at the cotyledon stage, early post (EPOST) with seedlings at the 4 fully expanded leaf stage and late post (LPOST) with seedlings at the 10 leaf stage.
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100 MALLOW PRE COT EPOST LPOST 80
60
40 Height, % of untreated Height, 20
0
0 50 100 150 200 250 300 350 400 Rate (kg ai/ha)
Figure A.3: Response (plant height) of four stages of common mallow (Malva neglecta Wallr.) growth to sulfentrazone. Nonlinear regression (full symbols) and raw means (empty symbols) are plotted with means combined over experiments for plant height at 21 d after treatment as a percentage of the untreated control. Stages of growth were: preemergence (PRE), cotyledon (COT) with seedlings at the cotyledon stage, early post (EPOST) with seedlings at the 4 fully expanded leaf stage and late post (LPOST) with seedlings at the 10 leaf stage.
118
100 PIGWEED PRE COT EPOST LPOST 80
60
40 Height, % of untreated Height, 20
0
0 50 100 150 200 250 300 350 400 Rate (kg ai/ha)
Figure A.4: Response (plant height) of four stages of redroot pigweed (Amaranthus retroflexus L.) growth to sulfentrazone. Nonlinear regression (full symbols) and raw means (empty symbols) are plotted with means combined over experiments for plant height at 21 d after treatment as a percentage of the untreated control. Stages of growth were: preemergence (PRE), cotyledon (COT) with seedlings at the cotyledon stage, early post (EPOST) with seedlings at the 4 fully expanded leaf stage and late post (LPOST) with seedlings at the 10 leaf stage.
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100 PURSLANE PRE COT EPOST LPOST 80
60
40 Height, % of untreated Height, 20
0
0 50 100 150 200 250 300 350 400 Rate (kg ai/ha)
Figure A.5: Response (plant height) of four stages of common purslane (Portulaca oleraceae L.) growth to sulfentrazone. Nonlinear regression (full symbols) and raw means (empty symbols) are plotted with means combined over experiments for plant height at 21 d after treatment as a percentage of the untreated control. Stages of growth were: preemergence (PRE), cotyledon (COT) with seedlings at the cotyledon stage, early post (EPOST) with seedlings at the 4 fully expanded leaf stage and late post (LPOST) with seedlings at the 10 leaf stage.
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100 WOODSORREL PRE COT EPOST 80 LPOST
60
40 Height, untreated % of
20
0
0 50 100 150 200 250 300 350 400 Rate (kg ai/ha)
Figure A.6: Response (plant height) of four stages of yellow woodsorrel (Oxalis stricta L.) growth to sulfentrazone. Nonlinear regression (full symbols) and raw means (empty symbols) are plotted with means combined over experiments for plant height at 21 d after treatment as a percentage of the untreated control. Stages of growth were: preemergence (PRE), cotyledon (COT) with seedlings at the cotyledon stage, early post (EPOST) with seedlings at the 4 fully expanded leaf stage and late post (LPOST) with seedlings at the 10 leaf stage.
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