THE BIOLOGY AND CONTROL OF
CENTAUREA DIFFUSA LAM. AND CENTAUREA MACULOSA LAM.
by-
Alan Kemball Watson
B.Sc. (Agr.) University of British Columbia 1970
A Thesis Submitted in Partial Fulfilment of the Requirements for the Degree of Master of Science in the Department of Plant Science
/
accept this thesis as conforming to the required standard
The University of British Columbia
May, 1972 In presenting this thesis in. partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study.
I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the Head of my Department or by his representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my
Written permission.
Department of
The University of British Columbia 8, Vancouver Canada
Date 2-^ (i)
ABSTRACT
Centaurea diffusa was found to infest 64,079 acres in the semiarid interior of southern British Columbia. C. maculosa has infested an additional 8,420 acres. These weedy plant species are common along roadsides-and in waste places and are spreading rapidly over vast areas of semiarid rangeland.
The density of the knapweed species could only be correlated with the degree of soil disturbance and was not correlated with any chemical property of the soil. The knapweeds are not generally grazed by domestic livestock and substantially reduce the forage yields in heavily infested areas.
C. diffusa and C. maculosa prevent soil erosion on disturbed sites as these pioneer species are capable of rapid colonization of these sites. These species are utilized to some extent as honey plants. However, the losses attributed to knapweed infestations generally override any potential use of the knapweeds.
Seeds of C. diffusa and C. maculosa germinate readily over a wide range of conditions. Continuous light was found to significantly retard the gemination of both species. The optimum temperature for germination of C. maculosa was found to be lower than that for C. diffusa seed. The optimum soil depth for emergence of both species was on the soil surface. C. diffusa seed did not emerge from soil depths below 3 cm. C. maculosa seed emerged from a soil depth of 5 cm.
Phenological data were recorded for both species. C_. maculosa begins to flower in early July with C. diffusa flowering approximately one or two weeks later.
The annual reproductive capacity of C. diffusa was determined to be 665 with C. maculosa exhibiting an annual reproductive capacity of 298. (ii)
Dual mechanisms of seed dispersal were observed for both species. Propagule dispersal is mainly by wind.
Cultural methods of control were generally found not to be beneficial in controlling the knapweeds. The knapweeds can be adequately controlled by using the herbicide picloram, 4-.amino - 3,5,6 - trichloropicolinic acid, however, the high cost of this herbicide has greatly limited its use. Phytophagous.insects, Urophora affinis and Metzneria paucipunctella, have been studied as potential biocontrol agents for the knapweeds. Initial releases of Urophora affinis indicate that the insect is capable of survival in the southern interior of British Columbia. The population has increased substantially since the initial release in 1970. It will take up to 10 years or more, however, before the releases of U. affinis are sufficiently well established to reduce the knapweed infestations.
Two fungal organisms, Sclerotinia sclerotiorium and Microsphaeropsis centaureae, were isolated from diseased C_. diffusa in the Vernon area. The potential of these organisms as biotic agents has, as yet, not been determined.
Weed control methods must be associated with other appropriate manage• ment practices to produce increases in forage yields. Such an integrated approach to the control of diffuse and spotted knapweed will substantially reduce the extent of the knapweed infestation in the southern interior of. British Columbia. (iii)
TABLE OF CONTENTS
Page
ABSTRACT • i LIST OF TABLES - ...... iv LIST OF FIGURES ...... • vii ACKNOWLEDGEMENT , ...... •••••• viii
I. INTRODUCTION • • • 1
II. DISTRIBUTION 2 A. Literature Review ...... • 2 B. Experimental Methods 5 C. Results and Discussion ...... 7
III. WEED ECOLOGY ... : 16 A. Literature Review •.... 16 B. Experimental Methods • • • • • 28 C. Results and Discussion • • . 33
IV. CONTROL , 51
A. Literature Review 51 B. Experimental Methods ••• • , 70 C. Results and Discussion ' 72
V. BIBLIOGRAPHY 91
VI. APPENDIX • • 100 (iv)
LIST. OF TABLES,.
Table Page
I Density scale utilized in the Centaurea survey ' 5 II Methods of soil analysis ,• 6 III. Acreage infested with Centaurea species in B.C 7 IV Plant density of knapweed infestations 9 V Average monthly and annual mean temperatures of selected sites .. .• ,.• 10 . VI Average monthly and annual precipitation and altitude of selected sites ', 11 VII Precipitation and mean temperatures of selected sites in 1971 ... . 12 VIII Chemical analysis of knapweed infested soils 14 IX Chemical composition of the above ground parts of Centaurea diffusa .(% dry wt.) ...... 21 X Chemical analysis of C. diffusa and C. maculosa in flower (% dry wt. ) .... . •. / 22 • XI Effect of C_. maculosa water extract on crop seedlings (7 days after sowing) 27 XII Effect of C. diffusa water extract on crop seedlings (7 days after sowing) ...... 28 XIII Yield of forage and knapweed from knapweed infested rangeland in the southern interior of British Columbia 34 XIV Weight of C. diffusa and C_. maculosa seed gathered in British Columbia' , 39 XV The effect of light on germination of C. diffusa -and C. maculosa seed (adjusted means).. 40 XVI Optimum germination temperatures for C. diffusa-and C. maculosa ,. • 43
XVII • Average seed production of C. ..diffusa and C. maculosa . .•. 46
XVIII Shallow plowing (7 cm) on C. diffusa in the fruiting stage (% cover) .... 51 ,(v)
Table Page
XIX- Plowing- (18 cm) on C. diffusa in the fruiting stage (%' cover) ._. -. 52 XX • Mowing of C. diffusa in the bolted stage (% cover) ..... 52 XXI Effect of burning on C. diffusa in the fruiting stage (% cover) ...... ' 53 / • . . . XXII Effect of picloram, reseeding, and complete protection from grazing by domestic animals on the control of C. - diffusa ..< ... • : • 54 XXIII 2,4-D (1 kg/hectare) applied to pasture infested with with diffuse knapweed in the rosette stage (% cover) . 54 XXIV Potential insect agents for the biological control of C. diffusa , ..... 59 XXV, Potential insect.agents for the biological control of C. maculosa ...... 60 XXVI Factors and responses involved in the host specificity of ovippsition in U. affinis • • •' • 63 XXVII Length of ovipositor; .and dimensions of oviposition site of some Urophora spp. • •••• ...... 64 XXVIII Urophora affinis. attack of Centaurea at B.C. release sites' ...... • 66 XXIX Effects of soil disturbance on C. diffusa populations ... 72 XXX Shallow plowing with later fertilizer application (10T fresh horse manure/hectare) (% cover) 73 XXXI The effects of mowing on knapweed • 74 XXXII Results of the East Kootenay Knapweed Control Program oc 1970-1971 75
XXXIII Treatments utilized to break sclerotia dormancy ? 80 XXXIV Determination of pathogenicity of Sclerotinia sclerotiorium and Microsphaerosis centaureae- on Centaurea diffusa and C. maculosa ...... 82 XXXV- Plant diseases observed on Centaurea species in North America 777777777. ,83 (vi)
Table - . Page
XXXVI Evaluation of biological control measures against weeds in Canada ' 87
Appendix Table I. Effect of temperature on germination of C. diffusa and C. maculosa ...... 100
Appendix Table II. . Effect of sowing depth on seedling emergence of C. diffusa and C. maculosa • 101 (vii)
LIST OF FIGURES
Figure Page
1 Distribution of C. diffusa in the U.S.A 4 2 Distribution of C.\ maculosa in the U.S.A. . .• 4 3 Distribution of C. diffusa in British Columbia .. 8 4 Distribution of C. maculosa in 'British Columbia ;. 8 5... Temperature gradient bar ,. 31 6j C. diffusa and C. maculosa seeds on temperature gradient bar 31 7 Pollen grains of C. nigra, C. maculosa and C. diffusa ... 38 8 C. maculosa, (upper) and C. diffusa seeds .. .. 38 9 The effect.of temperature on germination of C. diffusa and C. maculosa seed • 42 10 Seedling emergence of C. diffusa and C. maculosa 24 days after sowing at different soil depths ...... 43 11 C. maculosa, (left) and C. diffusa flower heads ...... 50 12 Fusiform gall in the receptacle of a C. maculosa flower, head , 61 13 Sclerotium in a C. diffusa, root 61 14 Apothecia produced from cold treated sclerotia 79 15 Plate culture of S_. sclerotiorium. 79 16 Plate culture of M. centaureae 81 17 Leaf spot on C. diffusa 85 18 Leaf spot on C. maculosa 85 19 Re-establishment of C. diffusa-after herbicide treat• ment at OK Falls, B.C 89 . 20 Re-establishment'of C. maculosa after herbicide treat• ment 'at Chase, B.C. •••• • 89 (viii)
. ACKNOWLEDGEMENT
I thank Dr. A.J. Renney for his interest and supervision throughout this study. The assistance of the other members of the committee: Dr. V.C. Runeckles, Dr. W.G. Wellington and Dr. R.J.'.Copeman is gratefully appreciated.
•In particular,.I am indepted to Dr..'R.J. Copeman for advice and materials in regard to the work with the fungal organisms. • I also thank Dr. G.W. Eaton, for assistance with statistical problems and Dr. R. Taylor for obtaining herbarium specimens. I thank Dr..R.J. Bandoni, Department of Botany, University of British Columbia; Miss M.E. Elliott, Plant Research Institute, Ottawa; and Dr. G. Morgan-Jones, Department of Biology, University of Waterloo for their valuable assistance in the identification of the fungal isolates.
I gratefully appreciate the co-operation of Dr. J.E. Miltimore, W.A. Hubbard'''and other members of the staff at the Canada Department of Agriculture Research Stations at Kamloops and Summerland. The interest and advice of Dr. P. Harris,.Research Institute, Belleville, Ontario is gratefully acknowledged. I thank F.'G. Smith, Department of Transport, Gonzales Observatory, Victoria for making weather data readily available. The assistance of the following British Columbia Department of Agriculture staff is acknowledged: E.L. Berry, J.C. Ryder, J. Corner and A.H. Bawtree.
The technical assistance of Miss M. Johnston, Miss A. Harris, I. Derics and J. Gibson is appreciated.
The co-operation of numerous ranchers in the Province is gratefully acknowledged. I thank Miss P. Jenkinson for the typing of the manuscript. The work was supported by the Bostock Grant'and by the National Research Council of Canada., I. INTRODUCTION
Centaurea diffusa Lam. (diffuse knapweed) and Centaurea maculosa Lam. (spotted knapweed) are two very troublesome weeds in the dry southern interior of the province of British Columbia. These aggressive, alien, pioneer species readily colonize disturbed sites and seemingly have the innate ability to withstand the competi• tion of the surrounding grass and herbage species and establish almost solid stands of• single species vegetation. Diffuse and spotted knapweed are common along roadsides and on waste ground. They have also- spread onto many acres of overgrazed or otherwise misused rangeland resulting in marked reductions in the productive capacity of these ranges. These weeds generally do not yield to the commonly . used weed control practices.
The following study was undertaken to determine the extent of the knapweed infestation in the southern interior of the province of British Columbia, to develop adequate control procedures for C. diffusa and C. maculosa and to develop a more comprehensive understanding of the biology of these two knapweed species. 2
II. . DISTRIBUTION
A. Literature Review
The earliest western collection of Centaurea diffusa Lam. was made in an alfalfa field at Bingen, Klickitat County, Washington, in 1907 by Suksdorf (39,59). The first British Columbia record was at Oyama in 1936 by, Tisdale followed by subsequent collections in 1939-40 by Eastham at Penticton and Grand Forks (9,12,33,93,9,5). However, Renney (71) pointed out that diffuse knapweed infestations occurred prior to 1930 as the weed was observed at Lytton and Pritchard at this time. Eastham (19) described the distribution of C. diffusa in .1947 as abundant in the Okanagan and spreading in the Grand Forks district. Renney, in 1959, described C. diffusa as being "well adapted to the dry interior" and indicated that the weed had infested the Fraser Canyon around Lytton, the Okanagan Valley, the Grand Forks area and the Cranbrook-Kimberly area. Since that time C_. diffusa has spread rapidly and colonized large acreages of dry land ranges and roadsides in the interior of British Columbia.
The first Canadian collection of Centaurea maculosa Lam. was made in 1893 at Victoria by Maeoun as C. paniculata (33). C. maculosa is very abundant along roadsides and waste places in the Canford area, near Merrit, on the west arm of Kootenay Lake and in the Slocan area (19,71). As is the case with C. diffusa., C. maculosa has also spread rapidly.
Frankton (28) has indicated that the Canadian distribution of
C. diffusa is. limited to southern British Columbia. Meanwhile, 3
C. maculosa has a wider Canadian distribution with large infestations in Ontario and Nova Scotia, but is most abundant in British Columbia (28).
C. maculosa and C. diffusa have a broad distribution in the United States of America and significant, increases in knapweed infesta• tions have been observed in the'.past ten years. C. diffusa has been observed commonly in fields, along .roadsides and in waste places in Washington, Oregon, Idaho, Illinois, Missouri, Iowa, Michigan, and Massachusetts (1,10,16,24,31,48,49,62,66,74,75,101). C. maculosa has a wider distribution than C_. diffusa in the U.S. and has been recorded in Washington, Oregon, Idaho, Montana, Massachusetts, New Jersey', Pennsylvanhia, Illinois, Kansas, Minnesota, Missouri, South Dakota,. - Michigan, Indiana, Vermont, Tennessee and North Carolina (1,10,16,17, 24,31,48,49,50,62,66,74,75,87,88 ,89',101). . C. maculosa is commonly found along roadsides, in waste places, in fields and in rangeland in the United States of America. Figures 1 and 2 illustrate the distribution °f £• diffusa and C.. maculosa in the U.S.A.
Roche (74) has indicated that a total of 378,585 acres in the State of Washington are infested with C_. diffusa with control measures having been attempted on only 6% of the area infested.
Popova (67) indicates that C. diffusa has a substantial area of distribution in eastern Europe and Asia. C. diffusa is common in Romania, Yugoslavia, northern Italy, eastern shore of the Mediterranean, Turkey, Greece, Bulgaria, Asia Minor and Syria. C_. diffusa is common in the U.S.S.R., especially the" Ukraine and the Crimea (67). 4
Fig.. 2. Distribution of C, maculosa in the 'J,S.A, (U.S.D.A. AgriTltodboofc (denser hatching - weed of greater economic importance) 5
B. . Experimental Methods
A recent survey of the southern interior of British Columbia has resulted in a comprehensive understanding of the distribution of these two weedy Centaurea species.
The knapweed survey included the following descriptions of each infestation; species, density, area, acreage, and location. A density scale, based on the Bran-Blanquet (8) system, was established to characterize the weed infestations according to plant frequency (Table I). The particular "area" where the infestation occurred was defined as follows: roadside verge - V; railroad rights-of-way - RR; rangeland - R; and field - F.
TABLE I.. 'Density Scale Utilized in the Centaurea Survey
C. diffusa x '• " 1 plant per 1/8 acre
1 1 plant per 1/8 acre to 1 plant per 100- ft
2 patches
3 1 to 110 plants per 100 ft2
4 10 to 100 plants per yd2 ... 2 ... 5 more than 100 plants per yd
C. maculosa x 1 plant per 1/8 acre
1 1 plant per 1/8 acre to 1 plant per 100 ft 2 patches
3 1 to 11 plants per 100 ft2 2 4 1 to 30 plants per yd 2 5 more than 30 plants per yd 6
With the distribution of C. diffusa and C. maculosa having been established within the province of British Columbia, analysis of some environmental conditions was attempted to explain the distribution of- . these two weedy plant species.
Plant density of the knapweed species varied considerably in the extensively studied areas in the Okanagan-Kamloops region. Soil samples from these sites were analyzed in an attempt to explain the variable plant densities observed in the C. diffusa and C. maculosa populations. Four soil samples were collected from each of eight . diffusa locations and three maculosa locations. The samples consisted of five -random 2 cm. diameter cores, 23 cm. in length, taken from within random meter square quadrats. The techniques utilized for the soil analysis are listed in Table' II. Data were analyzed by analysis of variance and simple linear multiple regression.
TABLE II. Methods of Soil Analysis
Measurement Method pH 1:5 soil:water suspension (pH meter) pH 0.01 M CaCl„ solution (pH meter) conductivity saturated paste - (conductivity meter) Nitrogen Semi-micro Kjeldahl Available phosphorus Bray P^ technique Sulphur Laboratory Equipment Corporation (LECO) analyzer Carbon Laboratory Equipment Corporation (LECO) analyzer Exchangeable cations Leaching with MLOAc (pH 7) and KC1 and utili- (Na, K, Mg, Ca) zation of the Perkin-Elmer Flame Spectrophotometer Total Exchange Distillation with semi-micro Kjeldahl Capacity Texture Hand method based on U.S.D.A. Textural Triangle 7
C. Results and Discussion
Figures 3 and 4 illustrate the distribution of C_. diffusa and
C. maculosa in British Columbia.
An estimate of the acreages infested by Centaurea species in the province of British Columbia is given in Table III.
TABLE III. Acreage infested with Centaurea species in B.C.
Species Acres
Centaurea diffusa 64,079 C. maculosa 8,420 C. repens 109 C. nigra (C. x pratensis) < \
The percentage of the infestations of C. diffusa,and C_. maculosa having a particular density classification (Table IV) indicate the capability for spread of both species and the establishment of numerous dense stands of Centaurea species.
i Fig. 3. Distribution of C_.' diffusa in British Columbia
Fig. 4. Distribution of C. maculosa in British Columbia 9
TABLE IV. Plant density of knapweed infestations
Density C. diffusa C. maculosa
X 16.0% 19.0% 1 8.5 19.5 2 3.5 0.5 3 16.0 16.0 4 33.0 19.0 5 23.0 26.0
Popova (67) suggested that the northern boundary of distribution of C. diffusa is approximately 53°N Lat., however, it extends further north only along railroad rights-of-way. This report suggests that C. diffusa, has a potential for extending farther north into the Cariboo area of British Columbia since -the northern limit of C. diffusa for this province is presently approximately 51°N. Lat.
Both Centaurea species appear to be well adapted to the climatic range of the southern interior of the province (Tables V, VI, .VII). C. diffusa has been observed at altitudes ranging from 500 to over 3,000 feet above sea level. Similarly, C. maculosa has been observed from 100 to over 4,000 feet above sea level. However, both species are most commonly found between 1,000 and 2,000.feet above sea level in the southern interior of the province. • C. maculosa has a more northern limit than.C. diffusa with a corresponding lower annual mean temperature range, 43°F-46°F. as compared to 45°F-49°F for the study sites in the TABLE V. Monthly and Annual Mean Temperatures (Average)
Jan. Feb. March April May June July Aug. Sept. Oct. Nov. Dec. Annual Years Averaged
Oliver 26 31 40 51 59 65 71 69 60 49 37 31 49 Penticton (A) .'; 27 31 39 '48 57 63 68 66 58 48 37 32 48 Summerland (C.D.A.) 26 30 39 49 57 63 70 67 60 49 36 30 48
Vernon 25 32 36 47 54 62 68 66 56 47 35 27 46 Vernon , (Coldstream) 22 26 36 47 56 61 67 64 47 46 34 27 45
Chase 25 31 36 47 55 62 68 66 57 46 35 29 46 10 Falkland 23 30 34 46 53 61 • 66 64 54 45 33 27 45 7 Kamloops (C.D.A.) '23 31 38 49 58 65 71 68 60 48 36 29 48 15
Sicamous 25 29 36 46 56 63 . 69 66 57 46 .34 28 46 11
Westwold 19 24 34 44 53 59 64 61 54 43 31 25 43
"Thirty year standard period average 1931-60.
Source: TDepartment of Transport, Gonzales^Qbservatory,..Victoria,- B. C. TABLE VI. Average monthly and annual precipitation and altitude of selected sites
April- Jan. Feb. March April May June July Aug. Sept. Oct. Nov. Dec. Annual Altitude Total
Oliver 1..3 8 0. 97 0.,8 4 0. 90 1,.3 9 1. 02 0,.7 7 1..1 6 0,.6 0 0. 69 1. 17 1..1 7 12 .06 1.,00 8 5.,2 4
Penticton 1..2 2 0. 89 • 0,.7 7 0. 73 1,.1 2 1. 35 0,.9 4 0.,7 7 0,.7 8 0. 94 1. 08 1,.1 5 11 .74 1.,14 0 4..9 1
Summerland 1..1 0 0. 84 0,.7 0 0. 68 1,.0 7 1. 35 0,.9 6 0..8 0 0,.7 7 0. 96 1. 01 1,.2 1 11 .45 1.,49 1 4..8 6
Vernon 1.,6 3 0. 96 0,.9 5 6. 99 1,.2 5 1. 56 1,.3 3 2.,1 0 1,.3 6 0. 84 1. 44 2..0 1 16 .42 • 1.,70 0 7.,2 3
Coldstream .57 1. 19 0,.9 1 .41 30 .10 1..1 5 1..1 9 38 1. 33 1..7 5 15 .41 ,582 5,.6 9 Ranch 1. 0. 73 1, 1. 1, 1. 1.
Chase 1..8 8 1. 39 0,.6 5 0. 91 1,.0 0 1. 48 0,.9 8 1.,3 5 1..4 0 0. 94 1. 38 1,.5 1 14 .87 1.,16 5 5..7 2 Falkland 2.,0 1 1. 34 0,.9 6 1. 03 1,,5 1 1. 26 1,.1 9 .1.,6 9 1.,6 0 1.1 1 1. 67 1,.9 3 17 .30 1.,50 0 6.,6 8
Kamloops 1.,3 2 0. 71 0.,2 8 0. 36 0.,5 9 1. 18 0,,8 8 1.,1 2 0.,8 4 0. 58 0. 72 0.,9 7 9..5 5 1.,15 0 4..1 3
Sicamous 2.,9 2 2. 00 1..3 1 1. 24 1,,8 7 2. 71 1..7 9 2.,2 0 2..2 8 1. 85 2.4 5 2..8 6 25 .48 1,,40 0 9..8 1
Westwold 1.,2 7 1. 08 0,.7 8 0. 66 1,.1 3 1. 68 1,.1 1 1.,1 9 1.,1 1 •1. 18 1. 10 1..4 6 13 .75 2.,02 0 5.,7 7
Source: Department of Transport, Gonzales Observatory, Victoria, B.C. TABLE VII. Precipitation and mean temperatures of selected sites in 1971.
Monthly Precipitation Monthly Mean Temperatures Mar. April May June July Aug. Sept. April- . Mar. "April May June July Aug. Sept. Aug.
Oliver 0. 62 0..3 6 0. 87 1.,3 6 0,.7 1 0,.5 6 1..1 2 3.,8 6 40., 1 46., 8 59. 5 61.. 3 68 .0 71. 6 55. 6
Penticton 0. 53 0,.6 5 1. 16 2. 39 0,.9 7 1,.3 2 0,.87 - 6,.4 9 36. 6 47., 1 57. 7 60,. 4 68 .5 72.4 56. 0
Summerland 0. 31 0,.1 8 1. 17 . 2.0 6 0,.4 7 1,.1 9 0,.7 6 5.,0 7 40. 0 45.,9 - 58. 2 59,. 5 69 .8 74. 0 56. 6
Vernon 0. 57 0,.0 9 •1.4 3 2. 64 0,.8 6 0,.9 3 0,.7 0 5,.9 5 38. 8 45., 0 57. 2 59,. 8 68 . 3 71. 5 55. 5
Coldstream 0. 54 0..2 8 2.4 7 2.4 1 1,.1 2 0..6 9 . 0..3 8 6.,9 7 37. 3 43. 6 57., 6 66 .6 71. 8 54. 1 Ranch •9 •55. 0,.0 2 1. 15 .54 Chase INC. 1. 57 0..6 1 0, 0..9 0 3.,8 9 INC. 45., 0 57. 9 . 59.,7 67 .5 70. 3 55.1 09 0.,1 7 1. 53 99 .48 .10 .56 Falkland 1. 2, 1. 1. 1, 7.,2 7 36. 2 43.. 3 55. 8 58., 3 • 66 .0 69.9 53. 3
Kamloops o.4 2 0..3 0 0. 95 1. 30 0..6 4 0..2 5 0.,4 1 3.,4 4 41. 2 47. 9 59. 0 62., 3 72 .0 74. 2 58. 1 0.,3 4 Sicamous 1. 02 2.4 0 4. 80 1,.7 2 1.,4 3 1..6 1 10.,6 9 37. 3 44., 2 . 57.4 59., 9 68 .2 71. 7 54. 7 0. 69 0..5 7 1. 49 1. 33 0,.6 0 ,00 0.,8 6 4.,9 9 35. 5 40. 8 53. 3 56. 64 68. 6 50. Westwold 1. ,2 .1 5
Source: Department of Transport, Gonzales Observatory, Victoria, B.C. 13
Okanagan- Kamloops region. The annual precipitation and the April-August precipitation ranges indicate that C. maculosa.is somewhat more tolerant to mesic, conditions. The presence of C_. maculosa in a dense roadside infestation in the relatively moist West Kootenay region exemplifies this point. The C_. maculosa infestation in the arid region near Walhachin can partially be explained by the increased moisture regime along the pavement edge of the old roadbed. C. maculosa in this area has not . spread substantially into the surrounding arid rangeland.
The soil analysis (Table VIII) indicates that the Centaurea species readily colonize different soils'with a wide range of chemical properties. Plant density of C. diffusa and C. .maculosa.could only be significantly (P = 0.05) .correlated with the degree of disturbance of the soil. The greater the degree of disturbance, the higher was the plant density, of the knapweed species. These results indicate, as Atkinson and Brink (6) had earlier suggested, that any soil in the dry southern interior of the province of British Columbia with a disturbed A horizon is subject to knapweed infestation. Marsden-Jones and Turrill- (55) indicated that the range of knapweeds in the British Isles is largely dependent on man-made or man-modified habitats.
C_. diffusa.and C. maculosa infest a substantial range of ecological habitats in the interior of British Columbia. Perhaps the apparent slight variation in species distribution of the knapweeds can be attributed,to time of propagule movement into a particular area as both C. diffusa,and C. maculosa, are adapted to similar climatic situations. However, C. maculosa, apparently is, somewhat more adapted to the cooler more mesic TABLE VIII. Chemical analysis of knapweed infested soils
''Diffusa Sites "Maculosa Sites D-l D-2 D-3 D-4 D-5 D-6 D-7 D-8 M-1 M-2 M-3
Plant density (/m2) 26.75 227.50 135.50 142.75 544.50 405.75 184.75 65.00 463.25 138.00 200.00 Disturbance Rating (1-3) 13223331333 pH (H20) 7.18 6.85 6.89 6.79 8.35 6.93 7.18 5.91 6.41 7.38 7.03 pH (0.01M CaCl2) 6.58 6.31 6.28 6.07 7.79 6.14 6.35 5.33 5.78 6.24 6.43 Conductivity (urn hos/cm2) 226.75 244.25 191.25 139.50 177.75 150.50 93.75 166.25 122.00 115.75 128.00 Sulfur (%) .065 .032 .031 .029 .021 .008 .020 .042 .042 .017 .014 Carbon (%) 3.47 1.42 2.91 0.95 0.88 0.51 1.43 4.04 3.64 1.34 1.86 Organic matter (% C-1.7) 5.90 2.41 4.95 1.62 1.49 0.87 2.44 6.87 6.19 2.27 3.15 Nitrogen (%) .319 .135 .238 .081 .061 .035 .117 .299 .329 .102 .117 C/N 10.99 10.50 12.35 11.87 13.98 14.98 12.35 13.80 11.50 14.22 16.51 Phosphorus (ppm) 2.05 1.45 2.25 1.83 1.85 1.83 2.23 5.43 2.20 2.80 3.03 Sodium (m.eq./lOOg) 0.858 0.098 0.083 0.138 0.220 0.265 0.180 0.130 0.120 0.075 0.165 Potassium (m.eq./lOOg) 3.670 1.670 1.185 0.983 2.468 2.825 1.688 2.155 1.733. 1.310 1.593 Magnesium (m.eq./lOOg) 12.110 2.015 1.608 1.703 3.458 1.265 1.843 3.470 2.608 2.860 4.33 Calcium (m.eq./lOOg) 11.935 6.345 10.153 4.548 16.030 4.273 7.560 10.200 10.153 9.655 11.000 Total Exchange capacity (m.eq./lOOg) 32.065 16.380 20.803 12.590 14.798 8.560 17.840 30.668 28.318 15.335 24.310 ''Sites: D-l Lac du Bois, D-2 Pritchard, D-3 Lavington, D-4 Summerland, D-5 Westbench, D-6 O.K. Falls. D-7 Myers Flat, D-8 Vernon, M-1 Chase, M-2 6-mile, M-3 Westwold. 15
conditions while C. diffusa readily colonizes semi-arid regions character• istic of a large portion of the southern interior of the province of
British Columbia. •16
III. .WEED ECOLOGY
A. Literature Review •
Centaurea diffusa and C. maculosa are members of the Cynareae tribe of the Compositae family. C_. diffusa is described as an annual, biennial, or short-lived perennial. Vorobiov (94), studying the biology of two year old weeds of the Danube steppe, described C. diffusa as a biennial, remaining in the form of a rosette, but sometimes flowering.
The species in British Columbia exhibits the biennial habit, but occasionally persists for a third season (triennial). Centaurea diffusa Lam. is described as "...pubescent becoming glabrate, rough, with an elongated taproot; Stems erect, 5-8 dm. tall, angled but not winged, branched near or above the base; Leaves alternate, the basal ones in a whorl, bipinnate to bipinnatifid, oblanceolate to oblong, up to 20 cm. long and 5 cm. wide, short-petioled, the ultimate segments narrowly oblong to elliptic, usually acute and wedge-shaped, the stem leaves sessile, the lower leaves bipinnate to bipinnatifid, the upper• most leaves bractlike and entire or minutely lobed; Flower heads solitary, more or less clustered at the ends of the branches, 1.5 cm. long; Involucre narrowly ovate or oblong, about 1 cm. long, woolly becoming glabrate and granular, the phyllaries leathery, nerved, the outer and middle phyllaries broadly to narrowly ovate, pale yellowish-green with a light-brown margin, the upper part narrowed into a stiff spine, the inner phyllaries lanceolate, tipped by a papery or leathery fringed appendage, spiny or spineless; Flowers white, pink or lavender, the outermost flowers sterile,- inconspicuous, with thread-like corolla lobes; Achene- oblong, 2.5 mm. .long, dark-brown, marked with several 17
conspicuous to faint, pale-brown or ivory lines; Pappus none, or on inner achenes as white chaff scales less than 1 mm. long". (4).
C. diffusa is native, to the eastern and southern Balkan Peninsula, southern Russia, and western Asia (93).
C. maculosa has also, been described as annual, biennial, or short-lived perennial. • The annual habit of C. maculosa has not been observed in British Columbia. The biennial habit and-more commonly the perennial habit have been observed with many plants being maintained for a period of at least four years. Centaurea maculosa Lam, is described as "... reproducing by seeds; Stems erect or ascending,, with slender wiry branches, rough-pubescent, 3-10 dm. high; Leaves alternate, pinnatifid, with narrow divisions, rough-divisions, rough-pubescent, the upper leaves often linear; Flower heads terminal and axillary, numerous and clustered, 1.5-2.5 cm. in diameter, many-flowered; Involucre pale, 1-1.4 cm. high, its smooth strongly ribbed out and median ovate phyllaries with firm points and 5-7 pairs of cilia, the dark tip 1-2 mm. long, the innermost phyllaries entire or fringed; Receptacle bristly, flat; Flowers all tubular, whitish to pink or purple, perfect, the marginal flowers enlarged, falsely radiate, neutral; Achene brownish, about 2 mm. long, notched on one side of the base; Pappus with a short tuft of bristles at tip end, 1-2 mwu long persistent" (4). C. maculosa is native to Europe.
The species' names characterize the difference between these two Centaurea species. Diffusa describes the diffuse or spreading habit of C. diffusa. Meanwhile, the name maculosa is derived from "macula" meaning •' spot' which aptly describes the spotted appearance of the flower heads due to the terminal blackish fringe of the bracts of the flower 18
head of C_. maculosa.
Hybridization between C. diffusa and C. maculosa has been regarded as a possibility because of variations which appear in the populations of C. diffusa. These C_. diffusa variants appear similar to typical C. diffusa with rigid terminal spines, but the flower color tends more toward the purple of C. maculosa and the bracts have the terminal blackish fringe which is a distinguishing characteristic of C_. maculosa. The achenes of these C. diffusa variants also exhibit a substantial pappus. Cytological studies by Moore and Frankton (60) indicate the chromosome complements of-C. diffusa as.diploid with 2n = 18 and C.. maculosa as tetraploid with 2n = 36. A hybrid between these two species would be expected to have the triploid chromosome number or 2n•= 27. However, Moore and Frankton did not find any plants with the triploid number indicating that hybrids did not occur between these two species in the collections from British Columbia. Dr. R.L. Taylor (91) has confirmed these results with a more thorough.investigation of the Centaurea populations in British Columbia. Taylor suggests that the degree of variation within the C. diffusa population is possible due to more than one introduction of the species into the area. He also . suggests that the variable genotypes expressed by flower color in C.- diffusa may be due to loose multiple gene control. Preliminary studies by Taylor indicate that C_. diffusa and C. maculosa have two distinct pigment systems which are responsible for the development of the variable flower color.
Saarisalo-Taubert (77), studying hybridization of Centaurea, section Jacea, in Finland, found hybrids and hybrid swarms between 19
members of the Jacea group of Centaurea common wherever the ranges of different species overlap. Hybrid plants (C. jacea x C_. nigra) or pure C. nigra were introduced into Finland but strong selection in favor of • the jacea genes has resulted in disappearance of pure C. nigra, popula• tions (77).
Simmonds (85) included C. diffusa and C. maculosa as non-toxic weed species of veterinary importance. The sharp spines, characteristic of many Centaurea species, can cause mechanical injury to the mouth and digestive tract of grazing animals resulting in considerable losses in beef production. Popova (67) indicated, even though C. diffusa was found to contain 0.07% alkaloids and 0.75% glucosoide, the harmful effect of diffuse knapweed is strictly mechanical in nature and no cases of poisoning have been recorded in Crimea.
The spiny nature of the mature diffuse knapweed plants causes considerable discomfort .to humans. Renney (71) pointed out that diffuse knapweed presents a dense barrier in many recreational areas in the southern interior of the province of British Columbia.
A number of Centaurea species, notably C_. repens and C. solstitialis, have been shown to be the causal agents of the disease, nigropallidal encephalomalocia, in horses (103,104). Horses exposed to nutritionally adequate rations (grass hay supplement in addition to the weed hay being tested) suffered from the disease. Nigropallidal encephalomalocia has been reported only in horses exposed to Centaurea species. Young et al. (103) suggested that any toxic principle that might be present in the plant is not accumulated or retained in the tissues of the horse which • 20
feeds on the weeds intermittently.
. Centaurea americanai'^, Nutt. has been characterized as a cyano- genetic plant producing considerable amounts of hydrocyanic acid (63). Further studies of the Centaurea genus will probably yield.other toxic compounds of importance.
Popova (68) has indicated the nutritive value of diffuse knapweed in the early,stages of growth' (Table IX). Centaurea. species in the flowering stage of development are very high in fibre content (Tables IX and X) and are not utilized as forage. Popova (68) suggested that in the winter, the leafless stems of C. diffusa become moistened and can again be eaten, but the mature stalks contain little nutritive value (Table IX).
Several Centaurea species are recognized as honey plants and C_. nigra, C_. jacea, and C_. cyanus are commonly utilized as sources of nectar in North America and Europe. Honey produced from C. maculosa in Virginia and Pennsylvania is described as light in color, mild flavored and of good quality -(53,54). The spotted knapweed is generally thought of as a weed in these areas but,, as one bee keeper explained: "the plant is not very prickly and has a most attractive appearance. Although it is a weed, it is one which could be tolerated even in a flower garden" (53). Maurizio and Grafl (56) reported that C_. cyanus produced approximately 5 mg. of nectar per day per flower head. Bees collected approximately 28 mg. pollen per plant from C. montana (56). However, pollen analysis showed only 1-4% of the sample was that of C. cyanus while clover and rape made up 96-99% of the sample (56). TABLE IX. Chemical Composition of the Above Ground Parts of Centaurea diffusa.(% dry wt.)
N-Free Plant Portion Date . Ash Crude True Fat Cellulose Collected Protein Protein Extrad
Spring Rosette 12/6/55 8.43 11.26 8.71 3.26 .33.62 40.31
Fall Rosette 7/9/55 7.12 10.23. 7.93 3.12 34.17 40.86 Bolting 14/5/55 7.29. 10.78 7.81 3.13 33.71 41.67 Budding 26/5/55 6.94 9.56 7.12 .2.94 . 34.31 42.13
Flowering 18/6/55 . . 6.24 9.42- 7.00 3.22 - 40.52 39.46
Fruiting 21/9/55 6.14 6.54 6.94 3.18 47.24 35.12 Autumn Hay- 17/9/55 6.12 6.42 5.42 0 44.32 0
Winter Hay 10/1/56 3.81 5.31 0 0 ' 48.63 0
Source: Popova (1964) TABLE X. Chemical Analysis of C. diffusa and C. maculosa in Flower (% dry wt.)
(a) C. diffusa
•N-Free Moisture Ash Protein Nitrogen Fat Crude Fibre' .Extract
Root 3.51 • 13.73 3.71 . 0.59 1.19 29.40 • 51.97
Stem 4.52 4.07 ; 2.74 0.43 0.80 41.80 50.59
Leaves 2.43 15.62 8.31 1.33 2.34 21.75 51.98-
(b) C. maculosa
Root 1.37 43.60 2.62 0.42 0.78 31.10 -
Stem 2.86 6.53 5.40 • 0.87 1.23 43.55 43.29
Leaves 3.73 16.18 5.68 0.92 2.87 16.85 46.42
Source: Fletcher (1961) 23
Knapweed seeds may form an important part of the diet of some birds. Birds may cause considerable damage to ripe or nearly ripe seeds. Marsden-Jones and Turrill (55) observed that goldfinches were extremely fond of knapweed seeds in Great Britain.
Coxworth et al. (15) have explored .the possibilities of utilizing dry land weeds as potential high protein seed crops for semiarid areas. Working with three Chenopodiaceae species which produced high seed- protein yield and drought resistance, Coxworth et al. found kochia and Russian thistle had comparable protein yields to flaxseed or rapeseed. Earle and Jones (18) suggested .that the Compositae family was one of the families which appears to offer outstanding promise as potential sources of new oilseeds. The utilization of range weeds such as Russian thistle or diffuse knapweed as high protein seed crops for semiarid areas may be of some importance in the future as world protein shortage continues to increase.
Besides the utilization of plant species as sources of high-
protein seed meals considerable interest and study is devoted, to the
search for chemical compounds such as alkaloids which may be of indus•
trial or medical use. Earle and Jones (18) found that C_. cyanus• and
C. americana were alkaloid positive species.,, Hultin and Torsell (45) also
found alkaloids present in plant parts of Centaurea species. Other workers
have found a vast array of chemical compounds in numerous plant species. •
The Compositae family offers considerable potential in the discovery of
new, useful chemical compounds of natural plant origin.
In certain parts of Europe C. diffusa is being utilized as a •
medicinal plant. Racz et-al. (69) suggested that it was feasible to . 24
utilize a number of Centaurea species, including C_. diffusa, as amara. Amara, or the Spanish word "amargos", is described as a vegetable drug with a bitter taste commonly referred to as "bitters". The medicine is thought to stimulate the appetite and to favor digestion. Racz et al. determined the bitter principle organoleptically in natural species (including C. diffusa) and found the bitter value of the aerial part in the concentration of 1:2000-3000.
An interesting aspect of the biology of C. maculosa has been described by Cavallit'o and Bailey (13) and more recently by Monya et al. (58) as the isolation of an antibacterial substance from the dry leaves of this species .• Cavallito and Bailey found that C_. maculosa yields approximately 1.5% of an unsaturated lactone antibiotic, C^g^gO^, from the dry leaves. It inhibits the growth of both gram positive,and gram negative bacteria. Monya et al. found the antibacterial principle of C. maculosa to inhibit the development of Salmonella typhi and Shigella shiga. The C.: maculosa antibiotic Is not being utilized, but it may be useful in the future since it induces little or no • development of resistant strains of bacteria.
Popova (67) indicated the C. diffusa seeds have germination rates of 90-100% and this rate is maintained under various conditions. Atkinson and Brink (6) found that germination of C. diffusa occurred in temperatures of 10°C to 25°C with 15°C to 20°C being optimum. They found germination rates in the order of 73% for current year seed and
74% for year old seed. Zednai (105) found C. maculosa seed exhibited 57.4% germination immediately after maturity and 86% to 100% germination
after;3 months... ;_v His studies revealed that germination of 25
C. maculosa seed was reduced to 67% after storage for one year at room temperature.
The knapweeds are entomophilous. The insect pollinators are seeking pollen and/or nectar. Marsden-Jones and Turrill (55) pointed out that insects favor cross-pollination with pollination of the British knapweeds normally brought about by nectar seeking insects. They found that an insect pushes down its proboscis successively into many florets with open corollas. Each floret is probed separately whether for pollen or nectar and a single insect can pollinate many florets without flying. Each floret has only one ovule requiring only one viable and compatible pollen grain for fertilization. Additional florets besides the one being probed may be fertilized by the insect. Marsden-Jones and Turrill observed that self-pollination by. recurving of stylar arms or stigmatic lobes does not occur, but 'own' pollen grains may be deposited on stigmatic surfaces since the florets in a capitulum develop acropetally over a period 1 to 2 weeks. Marsden-Jones and Turrill suggest that most knapweed species exhibit self-incompati• bility. However, Taylor (91) has found that C. diffusa and C. maculosa are both self-compatible.
Marsden-Jones and Turrill suggested that reproductive capacity of the knapweeds depends upon,'', number of reproductive seasons, number- of capitula per plant, number of potentially fertile florets, effective• ness of pollination and subsequent fertilization, number of cypselas produced, survival of cypselas, percent germination of the seeds, and establishment of seedlings. 26
Gland-tipped hairs and sessile glands were observed on the surface of leaves of the knapweed species by Ormrod (64). Ormrod and Renney (65) suggested that the development of trichomes on the surface of C. diffusa leaves results in a pubescence sufficient to influence retention or penetration of herbicidal sprays.
The ability of Centaurea species to readily invade disturbed sites and withstand competition from other plant species has been recognized for some time. The knapweeds appear to exhibit allelopathic effects on other plant species. Fletcher and Renney (27) confirmed the presence of an inhibitory substance in C.. repens, C. maculosa and C. diffusa with the leaves containing the highest portion of the inhibitor (Tables. XI and XII). Field observations indicate seedlings of the same species develop in close proximity to the parent plant partially ruling out self-toxicity. Fletcher-and Renney partially characterized the inhibitor as an indole derivative or as a precursor of auxin. These studies explain, in part at least, the aggressive nature of the Centaurea species which enable them to rapidly colonize disturbed sites and withstand the competition from associated plant species. TABLE XI. Effect of C. maculosa Water Extract on Crop Seedlings (7 days after sowing)
Germ Crop Extract Shoot Root • (%) (cm) (cm)
Lettuce Control H20 96 3.4 3.5 Leaf 80 2.6 1.5 Seed 80 2.0 • 1.9 Root 92 3.2 3.2
Barley Control H20 84 12.6 10.2 Leaf 72 7.8 6.5
Seed 84 3.5 . 3.6 Root 84 . 12.1 9.8
Source: Fletcher (1961)
TABLE XII. Effect of C. diffusa Water Extract on Crop Seedlings (7 days after sowing)
Germ " Shoot Root Crop Extract (%) (cm) (cm)
Lettuce Control H20 96 3.4 3..5
Leaf 84 2.6 1.0 Root 84 3.1 3.5
Barley Control H20 84 12.6 10.2
Leaf 72 7.7 6.4 Root 80 11.4 9.1
Source: Fletcher (1961) 28
B. Experimental Methods
Study areas were established at 13 sites in the Okanagan-Kamloops area. The 8 C.. diffusa and 5 C. maculosa sites were representative • knapweed infested areas in the interior of B.C. Five Centaurea plants within 1 meter square quadrats were choosen at random at each of the 13 sites. Phenological and developmental data were recorded on these plants throughout the 1971 growing season. Capitula were collected at random at each of the study sites and the number of seeds per head was recorded.
. Line transects were established through knapweed infestations, and random one meter square quadrats were harvested to include all plant growth. The forage species were separated from the knapweed and the samples were dried at 50°C for a period of 24 hours.
, Field observations'were recorded from knapweed infested areas throughout the southern interior of British Columbia during the summers of.1968, 1970 and 1971. «• 29
Laboratory Studies
(a) Preliminary germination studies
Germination studies were conducted on C„diffusa seed collected in the. spring of 1971 from flower heads which had retained a few seeds over the previous winter and on C. diffusa and C. maculosa seed collected in the late summer of 1970 and stored at room temperature for 20 months, C. diffusa and C. maculosa seed collected at Chase in the late summer of 1971 and stored for 3 days and 25 days at room temperature. Each test included two replicates of 50 seeds placed on moistened, sterilized No. 1 Whatman filter paper in glass petri dishes. Dishes were placed in a Seedburo germinator at 25°C. Percent germination was determined after one week.
(b) Effect of light on seed germination
Studies on the effect of light on seed germination were conducted in two Percival growth chambers with the temperature maintained at 25°C (± 1°C) and with controlled light conditions. All treatments were con• ducted by placing 25 seeds, of one of the knapweed species on moistened sterilized No. 1 Whatman filter paper in glass petri dishes. Seeds of C. diffusa and C_. maculosa were harvested in the late summer of 1971 and stored at room temperature until being utilized in the experiment. The light treatments included continuous light of 700 ft-c in the first chamber, and 16 hr. light of 700 ft-c followed by 8 hr. darkness in the
second chamber. Continuous darkness was maintained by wrapping glass petri dishes in aluminum foil and placing them in the first chamber. The whole experiment was conducted three different times with the light 30
conditions being altered between the two chambers. Three replicates of each species in each treatment occurred in all three runs.
Percent germination-was recorded after two, four, and six day periods. Seeds in the dark were removed and a new set of seeds was utilized for each period. Data were analyzed by the analysis of variance and by, simple linear multiple regression.
(c) Effect of temperature on seed germination
A linear temperature gradient bar was constructed after Timbers and Hocking (92) to study the effect of temperature on germination of C. diffusa and C_. maculosa seed. Under operating conditions temperature drift at any location along the bar was less than ± 0.5°C. Temperatures along the bar at which seeds were placed were 7°C, 10°C, 13°C, 16°C, 19°C, 22°C, 25°C, 28°C, 31°C and 34°C. The bar was sectioned off into ten compartments with insulation and each compartment was equipped with individual lids. The•removable lid further insulated the bar and maintained dark conditions (Figures 5 and 6). All seeds of C. diffusa and C. maculosa utilized in the study were collected in the late summer of 1971 and prior to the test were treated with 1:6 sodium hypochlorite solution to control fungi. Seven seeds of each species were placed in a row, perpendicular to the length of the bar in each of the compart• ments on moistened, sterilized No. 1 Whatman filter paper. The seeds were exposed to diffuse light for less than 30 seconds daily as percent germination was recorded. Water was added daily to maintain moistened condition at the warm end of the bar. The experiment was conducted three different times. The test was discontinued after two weeks.
32
However, no additional germination occurred after 10 days. Data were analyzed by the analysis of variance and by simple : ^curvilinear multiple regression.
Greenhouse Studies •
Studies were conducted under greenhouse conditions to determine the effect of seeding depth on percent germination and subsequent seedling emergence. Twenty-five seeds' of C_. diffusa were sown at depths of 0 cm., 0.5 cm., 1 cm., 3 cm., and 5 cm. in five different 5" plastic pots filled with greenhouse soil. The texture of the soil was determined as sandy, loam by the hand texture method. The treatments were replicated four times' and seeds of C. maculosa were treated in a similar manner. The pots were placed in a randomized complete block design. The temperature in the greenhouse was maintained at 45°C (±5°C). The amount of water held by.the greenhouse soil at field capacity, or 1/3-bar water tension, was determined and the soils were brought to field capacity daily by the addition of sufficient water to reach the required weight for each pot. Cumulative percent emergence and mortality of emerged seedlings were recorded daily. Data were- analyzed by the analysis of variance and by simple linear multiple regression. 33
C. Results. and Discussion....
The Centaurea.species with their rosette habit of growth, generally escape grazing. However, in the spring the plants bolt and are susceptible to grazing, but as the plants mature they become very woody and ,are essentially inedible. Cattle have been observed
grazing ;C. diffusa-quite,extensively on some of the ranges in the Pritchard area near Kamloops. This knapweed was in the bolted stage. No adverse effects have been observed or reported in these cattle populations.As the area is heavily overgrazed and the cattle are forced to eat the knapweed they may acquire a "taste" for the bitter knapweed.
Centaurea species are generally not utilized as forage species.,, and, in addition, interfere with the consumption of more desirable forage species below the dense, spiny, overstory of the knapweed infestations.
Knapweed infested rangelands have considerably reduced forage - yields. Selective grazing and the aggressive nature of the knapweeds tend to crowd out many palatable forage species. The large vegetative mass of the Centaurea species utilize substantial moisture and nutrients from the soil decreasing the potential forage production of other species on knapweed infested ranges.. Table XIII indicates the dry matter yields (kg/hectare) of infested and non-infested rangeland. These samples, were obtained from different rangeland conditions.. The data collected from the Summerland site indicate - the ability of C. diffusa to reduce forage yield on native range which is not utilized by grazing animals, however, •34
TABLE XIII. Yield of forage and knapweed from knapweed infested rangeland in the southern interior of British Columbia (Kg./he)
Lac du Bois Summerland Commonage - Chase Diffuse Forage • Diffuse Forage - Diffuse Forage Spotted "' Forage
0 1450 0 - 880 0 970 990 20 0 1440 0 920 0 940 , 1220 30 0 1150 0 ' 590' • 0 ' 630 1760 10 0 300 0 470 40 320 140 710 ,0 440 130 170 150 530 o 350 250 540 220 820 10 400 340 260 . 370 310 60 ,980 750 . 840 390 1100 150 400 820 750 660 210 . 290 • 530 850 220 770 20 * 0 1630 810 20 * 0 1700 820 70 * o 2060 890 20
^Random samples from range reseeded to crested wheatgrass 35
a portion of the area was severely disturbed by a pipeline right-of-way. The decrease in forage yield was significantly (5% level) correlated with increased production of C. diffusa. The two other diffusa, sites, Lac du Bois and Commonage, were located on rangeland which was utilized by domestic stock and indicate the problems of overgrazing with sub-, stantially reduced yields in the knapweed-free plots. Occasionally, relatively large forage yields were observed when the knapweed yield was relatively large, indicating that' the forage species may be present, but due to the dense, spiny overstory of C_. diffusa, cattle were unable to utilize the available forage. C. maculosa also reduces the forage yield to a point where the rangeland is not providing any available forage to the domestic grazing animal.
A well managed, reseeded dryland range may produce approximately 2000 kg. of forage per hectare as compared with 400 to 500 kg. of forage per hectare on native' range (Table XIII). Infestation of native range- lands with Centaurea species results in considerable reduction in actual yield and in available forage. Heavily infested rangelands are essentially non-productive.
McLean and Marchand (57) indicated that on the average 660 lb. of available forage is needed for a 1000-pound cow for 1 month (animal- unit month). Stocking rates can be estimated on the basis of acres per animal-unit month (AUM) from yield data assuming a 45% carryover. They suggested that "bluebunch wheatgrass - rough fescue" range in "good" condition producing on the average 800 lb. forage per acre would have an average stocking rate of 1.5. Knapweed infested range may produce 36
only 100 lb. of forage per acre resulting in a stocking rate of 12.0 acre per animal-unit month.
Losses in potential wildlife production are difficult to compute, but it could be speculated that a similar reduction in the deer popula• tion to that of beef'production would occur on rangeland heavily - infested with 'Centaurea species.'
Dryland hay is often infested with C. diffusa, or C. maculosa in the interior of B.C.. Knapweed infested hay is generally not palatable to livestock resulting in considerable losses. Popova (67) indicated that alfalfa fields in the- Crimea are heavily infested with C. diffusa with the knapweed comprising from 40-65% of the dry matter produced. The production of dryland hay is limited in the interior of British • Columbia and C.. diffusa and C. maculosa are generally not a problem in well managed irrigated hay fields.
Wodehouse (100) suggested that the Centaurea species, which are insect pollinated and exceptionally well adapted to this mode of pollination, are unlikely to cause hayfever. Therefore, work loss due to hayfever allergies cannot, be attributed to the presence of Centaurea species. However, the knapweeds can cause a mild discomfort if tasted which'can be utilized as a useful diagnostic technique.
It is difficult to place sale values on rangeland infested with knapweed, as compared to those ranges free of knapweed. However, the data in Table XEIIindicates the substantial losses in forage yield and subsequent reduction in beef production on rangelands heavily infested with knapweed species. The sale value of Centaurea infested rangeland 37
would undoubtedly be reduced to a low level.
The ability of the Centaurea spp. to establish readily in disturbed environments indicates their, usefulness as pioneer species. The rapid establishment of plant cover in the form of rosettes on barren soils prevents soil erosion. This plant cover also aids in the build up of organic matter in the soil.
Bees were observed in the Okanagan to be extensively working
C. diffusa, C. maculosa and C. nigra. Bees were collected and nectar samples were withdrawn. These samples were very bitter to the taste.
Samples of pollen collected by foraging bees were retained. The accom• panying photographs (Figure 7) of the pollen were taken of the three
Centaurea species utilized by foraging bees in the Okanagan (courtesy of.
J. Louveaux (52)).
It is apparent that C. diffusa and C. maculosa provide substantial pollen and nectar in the interior of British Columbia. These plants may be considered as valuable honey plants in waste ground, but they do not compare to the established honey plants such as clover and alfalfa.
The knapweeds cannot be regarded as having significant forage value due to their lack of palatability and high fibre content. Popova
(68) indicates the nutritive value of knapweed hay, but suggests that
C. diffusa may -be utilized only in the early bolting stage. The rosette habit of knapweeds enables the plants to escape grazing and the mature flowering -stalks are much too coarse with a very high fibre content. The disadvantages of these plant species heavily over-ride the potential value they may have as forage. Generally, the knapweed plants with.their tough, coarse stems and spiny flower heads are avoided 38
Coupe equatorial* - Ornementation Coupe meridierme vue polaire
B V
C
L Fig. 7. Pollen grains of C. nigra, C. maculosa and C. diffusa * A - C_. nigra; B - C_. maculosa; C - C. diffusa Source: Louveaux, J. (1971)
til?*
Fig. 8. C. maculosa (upper) and C. diffusa seeds 39
by grazing animals and are not particularly palatable to the livestock- and wildlife.
No actual observations of birds or rodents utilizing knapweed seeds in the interior of the province were made. However, numerous neat piles of C_. maculosa chaff were observed at Chase indicating possible rodent or bird utilization of the seed.
As described earlier, C. maculosa seeds are larger than C. diffusa (Figure 8). C. maculosa achenes have a substantial pappus whereas a pappus is generally absent .from C_. diffusa achenes. The average weight of C_. diffusa seed is 1.099 mg. with C_. maculosa seed weighing 1.778 mg. (Table XIV). Both of these species fall within the range of 'relatively large seeds' as described by Frenkel (29).
TABLE XIV. Weight of C. diffusa, and C_. maculosa, seed gathered in British Columbia
C. diffusa . C. maculosa Sample . wt. 100 seeds wt. of single' wt. 100 seeds wt. of single (gm.) seed (gm.) (gm.) seed (gm.)
1 0.1096 • 0.001096 0.1849 0.001849 2 0.1079 0.001079 0.1762. 0.001762 3 0.1109 0.001109 0.1702 0.001702 • 4 0.1126 0.001126 0.1788 0.001788 5 0.1089 0.001089 0.1789 0.001789 Mean wt. 0.001099 0.001778
The seeds of Centaurea species germinate readily over a broad range of environmental conditions. Marsden-Jones and Turrill (55) describe the germination process of C. nigra as follows: "The cypselas 40
are slightly compressed and at germination a longitudinal split. appears in the pericarp, developing from below upwards. This split occurs at one margin in the plane of .'compression.... The radicle grows through the split pericarp at the base of the cypsela". Cypselas of C_. diffusa and C_. maculosa were observed to germinate in a similar manner.
C. diffusa which was retained in the flower head' over winter exhibited 88% germination. . Seed of C. diffusa and C. maculosa exhibited 95% and 93% germination respectively after 20 months in storage at room temperature. Three day old seeds of C. diffusa and C. maculosa exhibited 40% and 20%(germmat^r^
, 68%~and_80%>germination'respectively.
TABLE XV. The effect of light on percent germination of C. diffusa and C. maculosa seed (adjusted means)
Species Treatment Treatment Duration (Days) Two Four Six Light 58c* 67b 72b Diffusa Dark 69b 83a 87a Light + Dark 69b 83a 87a
Light 58c 67b 72b Maculosa Dark 82a 83a 87a Light + Dark 69b 83a 8.7a
"Means for the same variable not sharing the same letter were signifi^ cantly different at the 5% level according to Simple Multiple Regression.
The results irr-.Table XV indicate that the continuous light treatment significantly (P = 0.05) reduced the percent germination of both Centaurea species after two, four and six days. The dark and the 16 hr. light plus 41
8 hr. dark treatments were not significantly different at the .5%.level after four and six days for both species. However, after two days, germination of C. maculosa in the dark was significantly higher than C_. diffusa.in the dark and significantly higher than both species in the light plus dark treatment. After four and six days the germination of C. maculosa in the dark was no longer significantly higher than that of C. diffusa in the dark, or both species in the light plus dark treat• ment. C_. diffusa and C_. maculosa germinating under natural conditions • would not be affected by, light duration.
The results shown in Appendix Table I and Figure 9 indicates that germination of C_.- diffusa .and C_. maculosa occurs in the range of 7°C to 34°C. Germination of over 80% occurs in the range of 10°C to 28°C for C. maculosa and in.the range of 13°C to 28°C for C_. diffusa. Analysis indicated that- after two days in the temperature treatments C. maculosa had a significantly higher (P = 0.05) percent germination than C_. diffusa at temperatures of 13°C and 16°C.. Germination of both species appeared to be delayed at the cooler temperatures with C_. maculosa showing higher cumulative percent •germination at the lower temperature
C7°-10O) than C. diffusa at the end of the experiment. C_. diffusa had a higher percent germination at the warmer temperature (34°C). The optimum temperatures were calculated from the fitted curves from the regression analysis (Table XVI). These results suggest that C. maculosa will germinate at slightly, lower temperatures. than C_. diffusa partially explaining the more northern distribution of C. maculosa. 42
Fig. 9. The effect of temperature on germination of C. diffusa and C. maculosa seed
A) C_. diffusa - two days after sowing B) C. maculosa -two days after sowing C) £. diffusa - ten days after sowing D) C_. maculosa -ten days after sowing TABIJB XVI. Optimum germination temperatures for 143 C. diffusa and C. maculosa
Time after Optimum temperatures (°C) sowing (days) Maculosa Diffusa
1 22.9°C 25.5°C 2 21.6 23.0 3 20.8 21.8 4 20.3 21.0 • 5 19.6 20.6 6 19.4 20.6 7 19.4 20.5 8 19.0 20.5 9 19.0 20.5 10 19.0 20.5
Fig. 10. Seedling emergence of C. diffusa and C. maculosa 24 days after sowing at different soil depths.
0 0.5 1 3 5 Depth of sowing (cm.)
V * M - C. maculosa; D - G. diffusa 44
Twenty-four days after sowing C_. maculosa exhibited a significantly (P-= 0.05) larger cumulative percent emergence than C_. diffusa at all sowing depths (Figure 10 and Appendix Table II). The optimum sowing depth for each species was at the soil surface. Emergences,from sowing depths of 0.5 cm. and 1 cm. were not. significantly different for either species. There was a significant (P = 0.05) decrease in percent emer• gence as depth was increased from 0 cm. to 0.5 or 1 cm. , from 0.5 or 1 cm. to 3 cm. and from 3 cm. to 5 cm. C. maculosa seed is capable of emer• gence at the 5 cm depths. C. diffusa did not emerge from depths below 3 cm. which confirms Popova's (67) findings. The larger seed of C. maculosa apparently enables this species to establish seedlings -from greater soil depths.
Seedling mortality was recorded during the above emergence study. Under greenhouse conditions 7.6% and 4.0% of the C. diffusa and C. maculosa seedlings, respectively, died. Mortality was primarily due to damping-off fungi and occasionally to the lack of chlorophyll. Seedling mortality in the field was observed to be over 55% in some instances, but generally appeared to be approximately 12%. Further studies are warranted to determine the actual field mortality of seedlings of the' Centaurea species in the interior of British Columbia.
There does not appear to be any morphological difference between seedlings of C. diffusa and C. maculosa, little variation being evident between the cotyledons and juvenile leaves of the two species. The first true leaves were observed under greenhouse conditions approximately two weeks, after emergence. 45
Both species 'form rosettes which are the over-wintering stage. Morphological differences between rosettes of C. diffusa.and C. maculosa are uncommon. The rosettes generally consist of 10 leaves but may range from 6 to 28 individual leaves. The much divided leaves are on the average 6.6 to 7.1 cm. long. Rosette mortality is rare. The rosettes of C. diffusa appear to require a cold period to induce transition to flowering. Thus seedlings established in the spring were not observed to complete their life cycle and produce viable seed in their first season of growth. Greenhouse studies indicated the ability of C_. maculosa to produce viable seed in one season of growth.
Transition to flowering (bolting) of the knapweed species occurs in early May in the interior of B.C.. C. diffusa rosettes produce only one stem but occasionally two stems have been observed. C_. maculosa rosettes produce one to six stems and perennial plants have been observed to produce 15 or more stems. Stem height of C_. diffusa plants is from 10 to 20 dm. whereas C. maculosa plants are .20 to 30 dm. tall.
Formation of the numerous reproductive flower buds can be observed in early June. Flowering occurs in July and August with initial flowering of C. maculosa being observed in the first week of July with C. diffusa flowering approximately two weeks later. Mature seeds were formed by mid-August.
The data in Table XVII indicates the average seed production per- plant of C_. diffusa and C. maculosa under semiarid rangeland conditions in the interior of B.C. . Assurrdng 80% germination, the annual reproduc• tive capacities of C. diffusa and- C... maculosa are 665 and 298 respectively. 46
Reproductive capacity was also determined for the knapweed species growing under irrigated conditions at the Canada Department of Agriculture, Research Station, Kamloops, B.C.
TABLE XVII. Average seed production of C. diffusa and C. maculosa
Annual Flower heads Seeds per Seeds per Reproductive per plant head plant Capacity
C. diffusa 66.5 12.5 832.3 665 . C. maculosa 14.0 26.6 372.4 298 irrigated C. diffusa • 1403.7 13.0 18,248.1 14,599 irrigated C. maculosa 706.7 35.8 25,299.9 20,240
Vegetative reproduction does not occur naturally in C. diffusa populations. C. maculosa does exhibit vegetative spread. A number of lateral shoots arise just below the soil surface and grow horizontally for approximately 3 cm. then form a rosette. These rosettes generally flower the following season but do not normally become detached from the parent rootstock. . This form of vegetative reproduction confers the perennial habit observed in many C. maculosa populations. The triennial habit observed in some C_. diffusa populations arises from regrowth of parent rootstock and not from the- development of lateral shoots.
Seed dispersal of C. diffusa is mainly by wind as mature plants often break off at ground level and function as tumbleweeds (67,71). 47
Atkinson and Brink (6) pointed out that dispersal close, to the parent plant is facilitated by horizontally placed involucres, which open as dehydration occurs, dropping their achenes readily.- Renney (71) found that C. maculosa populations extend largely through peripheral enlarge• ment' of the existing stand. C_. maculosa exhibits a 'flicking' action which spreads seeds up to several feet from the parent plant.
Marsden-Jones and Turrill. (55) indicated that the presence of a pappus on the achene has little or no effect in enhancing•dispersal efficiency.
Field observations suggest that both C_. diffusa and C. maculosa have dual mechanisms of seed dispersal. The dual seed dispersal enables
these species to rapidly colonize the vicinity near the parent plant and
to establish new populations some distance removed. The 'flicking',
action of C. maculosa 'suggests a spring-like action. The apparent
ability of the C_. maculosa achenes to be propelled from the receptacle
is due tp dehydration ...The bracts of the flower heads open up enabling
the loosely held achenes to be expelled from the head if movement of the plant stems occurs (Figure I'D." Agents such as insects, wind,, or animals
cause sufficient movement and .subsequent release of the achenes. The released C. maculosa achenes, with their substantial pappus, may become
attached to passing animals and. transported some distance from the parent plant. Both knapweed species are common along roadsides in' the
dry interior .and well adapted to 'seed dispersal along routes of travel.
C. diffusa plants readily become attached to vehicles and achenes are
individually dispensed through-, the relatively small distal opening in
the receptacle (Figure 11). C_. diffusa and C. maculosa achenes may also be transported by mud adhering to vehicles. The pappus of 48
C. maculosa achenes does not facilitate wind dispersal.
The normal development of C_. diffusa and C. maculosa plants involves the production of entire juvenile leaves followed by the production of the more typical much divided adult leaves. The rosette habit is lost when the plant undergoes transition to flowering and the formation of lobed- leaves ceases with the formation again of smaller, entire leaves. The development on one plant of leaves of various shapes is termed heteroblastic development. Feldman and Cutter (22,23) studying the regulation of leaf form in Centaurea solstitialis L. have evidence suggesting that endogenous gibberellins affect the type of leaf produced. They speculate that when the seed germinates the first-formed, simple, entire leaves are partly a response to high levels of endogenous gibberellins. The commencement of lobed-leaf formation may occur due to GA levels being reduced. When plants undergo the transition to flowering, endogenous gibberellin levels rise again as reflected by the production of small entire leaves. Feldman and Cutter propose "...a gibberellin.or gibberellin-like system operates in the whole plant to modify or regulate the type of leaves produced in the heteroblastic series".
The commonly associated plant species observed in the knapweed
infested areas of the interior of the province of British Columbia included:
Achillea lanulosa, Agropyron spicatum, Artemisia frigida, Balsamorhiza sagittata,
Bromus tectorum', Festuca idahoensis, .F. scabrella, Koeleria cristata, Lupinus
sericeus, Poa pratensis, P. secunda, Stipa comata, Taraxacum officinale,
Lappula echinata, Tragopogon pratensis, Gypsophila paniculata, Verbascum
thapsis, Potentilla spp. , Rumex acetosella,'Chrysothamnus nauseosus,.
Astragalus spp. , Antennaria umbrinella. Forage species such as bluebunch wheatgrass and rough fescue are being replaced by other, less desirable, grass species such as Sandberg's bluegrass and downy brome and weedy species such as knapweeds and sages on most of the ranges in the interior of British Columbia. 50
Fig. 11. C. maculosa (left) and C. diffusa flower heads 51
IV. CONTROL
A. Literature Review
Knapweeds do not generally present problems on cultivated land. Therefore, on land which is plowable, control of C. diffusa and C. maculosa can be readily achieved. Atkinson and Brink (6) pointed out that regeneration from "plowed-under crowns" was not frequent, but incompletely covered crowns regenerated readily. Popova (67 indicated that as a result of. shallow plowing knapweed seeds which had been more than 3 cm. under the surface were brought to the surface and in subsequent years knapweed flourished on these plots (see Table XVIII). However,
TABLE XVIII. Shallow plowing (7 cm.) on C. diffusa in the fruiting stage (% cover)
Just before Control Treatment Treatment
1955 .1956 1957 1958 1955 1956 1957 1958
Grasses 6.0 4.5 3.6 4.1 6.3 4.5 3.9 3.6 Herbage 22.8 18.6 13.2 13.5 21.9 18.3 13.7 13.3 Knapweed 71.2 76.9 83.2 82.4 71.8 77.2 82.4 83.1
Source: Popova (1960)
Popova (67) found that deep plowing (Table XIX) brought about the elimina• tion of knapweed with subsequent vigorous grass growth. 52
TABLE XIX Effect of plowing (18 cm.) on C. diffusa in the fruiting stage (% cover) Just before Control Treatment Treatment
1955 1956 1957 1958 1955 1956 1957 1958
Grasses 1.0 7.4 8.5 6.'3 1.3 78.4 80.6 83.3 Legumes - 0 0 0.6 0.2 0 0 0.7 3.4 Herbage 14,. 0 10:. 2 10 .:4 ••.'.9.1 1375' 20.2 17.4: 12,.7> Knapweed 85.0 82.4 80.5 84.4 85.2 1.4 1.3 0.6
Source: Popova (1960)
Popova (67) indicated that mowing actually increased the population of C_. diffusa .(Table XX) in subsequent years following treatment. It has been observed that the Centaurea species -are capable of resisting the action of mowing, not only by their rosette habit, but also by secondary flowering below.the original cutting height. Marsden-Jones and Turrill (55) observed a period of secondary flowering in the British knapweeds after mowing with capitula being produced in September.
TABLE XX. Mowing of C. diffusa in the bolted stage (% cover)
Just before Control Treatment Treatment
1955 1956 . 1957 1958 1955 1956 1957 1958
Grasses 20.6 22.2 18.2 15.3 22.4 9.1 3.1 2.5 Herbage . 32.0 . 25.5 23.4 22.3 30.2 18.5 13.5 11.4 Knapweed 47.4 52.3 58.4 62.4 47.4 72.4 83.4 86.1
Source: Popova (1960) 53
Popova (6-7) indicated that burning was an effective control measure
for" C. diffusa • (Table XXI).. He found that rosettes appeared after the- burn and developed the following year, but within two years the knapweed almost completely disappears from the grass sward due to the strong growth of the associated grass species. Zednai (105) found that a simulated range fire substantially reduced the germination percentage of .C. maculosa from 69% to .3%.
TABLE XXI. Effect of burning on C. diffusa.in the fruiting stage (% cover)
Control ^^f"*" ^f"^0^6 Treatment Treatment 1956 1957 1958 1956 1957 1958
Grasses 12.5 10.4 8.3 ' 12.3 57.5 92.1 Herbage 10.4 10.1 9.2 9.6 . 5.3 6.3 Knapweed 77.1 79.5 82.5 78.1 37.2 1.6
Source: Popova (1960)
r Hubbard (40,41) has established plots to determine the.effects of several variables on C. diffusa. These include picloram herbicide, com-'' plete protection from domestic grazing, and reseeding with crested wheat- grass. His results (Table XXII) indicate that forage production can be substantially increased through proper management practises in dryland' situations. Where native grasses, have been substantially reduced, reseeding native range to crested wheatgrass shows considerable promise in increased forage yields. 54
TABLE XXII. • Effect of picloram, reseeding, and complete protection from grazing by domestic animals on the control of C_. diffusa
Forage yield Treatment (# ^ matter/acre) 1968 1969 1970 ' 1971
1. Check 77 221 234 252 .2. Seeded to crested wheatgrass 66 384 377 352 3. 4 oz. Picloram + crested wheatgrass 102 340 . 399 460 4. 8 oz. Picloram + crested wheatgrass 61 127 192 350
Source: Hubbard (1971)
The Centaurea spp. are deep rooted biennials to short live perennials which do not readily yield to the application of chemicals. However, Popova (67) found that 2,4-D at the rate of one kg per hectare completely eliminated diffuse knapweed and associated forbs in badly infested pastures in the Crimean (Table XXIII). Similarily, Furrer and Fertig (30) reported complete control of C. maculosa with 2,4-D amine or 2,4-D low volatile ester at the rate- of 1.5 lb. per acre and also with dicamba.-
at the rate of 1 lb. per acre.
. TABLE XXIII. 2,4-D (1 kg/hectare) applied to pasture infested with diffuse knapweed in the rosette stage (% cover)
n 4-. -, Just before „ , , . Control Treatmenrn . t. Treatment 12/6/56 14/6/57 . 16/6/58 12/6/56 21/6/56 14/6/57 16/6/58
Grasses 10.2% 16.9% 4.2% 10.2% 93.6% 91.2% 90.5% Herbage 19.4 .18.3 19.6 19.4 6.4 8.8 9.5 Knapweed 70.4 64.8' 76.5 70.4 0.0 0.0 0.0
Source: Popova (1960) 55
Renney and Hughes (72) indicated that trials using 2,4-D were begun in 1952 in British Columbia to control diffuse knapweed. Control of C. diffusa was'temporary and the chemical application of 2,4-D did not prevent heavy seedling establishment in the fall. Due to the re- infestation of C_. diffusa and C. maculosa after 2,4-D treatment in
British Columbia, further chemical trials were conducted. Renney and
Hughes found that picloram (Tordon) exhibited the superior selective control of C. diffusa and C. maculosa on semiarid rangeland sites in the interior of British Columbia. Picloram is presently recommended at the rate of 6-8 oz. active ingredient per acre for the control of
C. diffusa and C. maculosa in the southern interior of British Columbia.
They indicated that at least two years residual control "has placed it in the category of an 'economical control practice'". Ryerson and
Sonder (76) have also indicated the beneficial effects of picloram for the control of spotted knapweed.
Picloram, 4-amino-3,5,6-trichloropicolinic acid, has a relatively low mammalian toxicity and is rapidly excreted from the animal body. The chemical is extremely phytotoxic to broadleaf plant species with grass species only moderately affected. It acts as a growth regulator.
Sharma et al. (83) found that the leaves and roots of Canada thistle (Cirsium arvense (L.) Scop.) readily absorbed picloram and that the leaves, but not the roots, retained a substantial portion of the picloram absorbed. Scifres et al..(81) observed that the concentration of picloram, applied at the rate of h lb/a with 2,4,5-T at \ lb/a, was reduced by 93% in herbaceous broadleaf plants by 30 days after herbicide 56
application. . They also found that picloram, at the above rate, usually dissipates from the- soil within 90 days under warm, dry conditions of semi arid rangelands (82). They suggested that the data indicates a low•probability of - picloram 'transport in runoff water unless a heavy rainfall occurred'immediately after herbicide application. Goring and Hamaker (32)- found movement of picloram by volatilization and runoff in field conditions was negligible. They indicated that the estimated half-order constants, ¥^ , of picloram in Canada was in the order of -.0.2. Therefore, at rates of 1 oz. and 2 lb/acre the time required for the herbicide to decompose to a level of 0.01 oz/acre would vary from 4.5 months to 4.6 years.
Picloram has been found to effectively control many undesirable woody plant species and many herbaceous weeds-. However, little concern has been directed towards the effect of picloram on desirable forage grass species. Scifres et al. (82) found that grasses absorbed picloram from the soil without forage production being adversely affected. More recent studies by Scifres and Halifax (80) showed root production of seedlings of switchgrass (Panicum virgatum L.) and sideoats grama (Bouteloua curtipendula (Michx.) Torr.) was decreased when 1 or 2 ppm picloram were placed on the soil surface. They also observed chlorotic and epinastic effects to the topgrowth of the seed• lings of these two grass•species. Scifres and Halifax stated: "... picloram applied just prior to or following range reseeding or applied to badly depleted rangeland could further complicate rate of seedling establishment". 57
The role of natural enemies-parasites, predators, and pathogens in reducing the population of a plant, or animal species is known as biological control (3). The biological control of weeds has been reviewed by a number of authors (3,4-2,43,96,97,99,107) and a number of striking successes have been recorded notably with the Opuntia spp. in Australia and the control of Hypericum perforatum in California.
Huffaker (42) points out that the goal of biological control is the reduction of a pest population to a non-injurious level, and not eradication. A potential biocontrol agent must not only be capable of destruction of its plant host, but also be limited by the availability of its host as a food supply or reproduction.site. Huffaker and Andres
(44) listed the following qualities of a good biological agent:
1. ability to kill plants or prevent reproduction in some direct or indirect way,
2. high ability to disperse and locate host plants,
3. good adaptation to the weed host and the. environmental conditions over a maximum part of terrain infested by the weed,
4. reproductive capacity sufficient to overtake the increase of its host without too much delay when for any reason control is temporarily short-circuited.
Biological control is by its nature very selective and is most useful where a single aggressive weed is troublesome (3). Most of the serious weeds in North America are alien and their aggressiveness is usually attributed, in part, to the absence.of their natural enemies. The decision to release exotic natural enemies to control an alien weed must be preceded by extensive -studies to determine the safety or host specificity of the biocontrol agent. Harris and ZwOlfer (38,113) 58
described the limitations of standard methods of determining host specifi• city of insects (starvation and negative-ovipo'sition' /tests), and have suggested the studies should be broadened to include the following:
1. study of the insect's biology, including host plant records with particular attention to adaptations likely to restrict host' ranges, 2. review of the plants attacked by related insects, . 3. determination of the laboratory host range of the insect, 4. investigations of the chemical or physical basis of host-plant recognition, 5. starvation tests on economic plants to confirm the limits of the previously established host range, 6. establishment of the insect's potential effectiveness for weed control.
Since 1961 ZwOlfer (106,108,109,111,112) has conducted an extensive survey in Europe to obtain information on phytophagous insects attacking wild Cynareae (Compositae) with the eventual hope of introdu• cing phytophagous insects into Canada for the biocontrol of thistles and knapweeds. The following lists pf promising insects for the control of Centaurea diffusa and C. maculosa were developed from Zwolfer's reports (Tables XXIV and XXV).
Numerous other phytophagous insects have been observed to damage Centaurea diffusa.and C. maculosa in,the European studies, but because of damage to economic crops such as artichoke or safflower or because of climatic limitations, have been excluded from the above lists • .. 59
TABLE XXIV. Potential insect agents for the biological control of C. diffusa
Insect Type of damage
Urophora affinis (Trypetidae) galls within receptacle of flower head
Metzneria sp. "Z" (Gelechiidae) larvae feed within receptacle and achenes of flower head
Chaetorellia sp. '-'.(Trypetidae) larvae destroy young florets, ovarioles, receptacle, and achenes
Sphenoptera jugoslavica larvae mine within root-stock (Buprestidae) ~ of the rosette and within the stem of the mature plant
Pseudeucosma caecimaculana larvae mine within the peri• (Tortricidae) pheral tissues of the root
Arima marginata (Galerucinae) adult and larvae feed on leaves
Sphaeroderma rubidum adults feed on leaves and shoots, (Chrysomelidae) larvae mine within the leaves nr. Aceria grandis (Eriophydae) gall mite transforming single florets into sterile leaves
Pterolonche sp. (Gelechidae) larvae mine within the. root
Cyphocleonus tigrinus larvae mine within the stem (Curailionidae)
Source: Zwolfer (1965, 1969, 1970, 1971) •60
TABLE XXV. Potential insect agents for the biological control of C. maculosa
Insect Type.of damage
Urophora affinis (Trypetidae) galls within receptacle of flower heads
Metzneria paucipunctella larvae feed within flower (Tortricidae) heads and destroys achenes
Euxanthoides straminea (Phalonidae) larvae mine within stems, roots, and flower buds
Chaetorellia hexachaeta (Trypetidae) larvae mine within receptacle and destroys achenes
Terellia virens (Trypetidae) larvae destroy the achenes
Source:- ZwOlfer (1965, 1969, 1970, 1971) r~"
ZwOlfer (110) has conducted an extensive study on the host specifi• city and life history of Urophora affinis Frfld. (Dipt., Trypetidae). U. affinis adults appear in the field during May-June and even in July. When bud development occurs on the host plant the males and females assemble on the panicles of the Centaurea species where mating occurs. Females deposit eggs two or three days after emergence and deposit about one hundred and twenty eggs. The closed flower buds are carefully probed before deposition. Eggs are deposited singly .or in small groups on the . small, undeveloped tubular flowers into the tissue of the receptacle. After three or four days the first instar hatches and penetrates the ovariole of the undeveloped -tubular flower where it mines and causes the latter to develop into a fusiform gall (Figure 120. Normally one to three galls per flower head are formed but there may be up to eight 61
Fig. 12. Fusiform gall in the receptacle of a C. maculosa flower head
I • I. . , . .r—uj MM i rt 1111111II {11«11 r I i; illllliniimimillllll Fig. 13. Sclerotium in a C. diffusa root 62
galls formed in each flower head. The third ins tar larvae remain in dia• pause within the gall .until early summer then pupate after turning so their head is oriented to the distal opening of the gall. Adults emerge in two or three weeks. The insects overwinters in the pupal stage. ZwSlfer stated that "the effect of U. affinis upon its host plant consists in the destruction of achenes and in the deformation of the receptacle of the capitulum which leads to a reduction of the production of viable seeds". Table XXVI summarizes the factors and responses involved in the host specificity of the oviposition of U. affinis.
These studies have led ZwOlfer to•conclude "the central-European populations of U. affinis (which are associated with C. maculosa) as "safe" for introduction to Canada for the following reasons: (a) The available field records suggested and extended oviposition tests made in the laboratory showed that "the central-European population of U. affinis are highly specialized in their host selection; (b) An experimental analysis of the orientation of U. affinis females showed that the females select a host plant and oviposition site using a com• bination of mainly or exclusively physical recognition tokens...; (c) Our study of U. affinis and other cecidocole Urophora spp. showed that in this genus the length of the ovipositor is closely adapted to the dimensions of the oviposition site.... . Thus, the heads of the•culti• vated Cynareae spp., artichoke and safflower are for mechanical reasons not accessible to U. affinis (Table XXVII); (d)...the cecidocole habits of the U. affinis larvae are a criterion for the narrow host range of the species, since gall formation involves close physiological adapta• tions of the gall maker to the host.plant: (e) Inspite of the occurrence 63
TABLE XXVI. , Factors and responses involved in the host specificity of op• position in U_. affinis
Phase of orientation - Property of the host plant Responses of the • which attracts or guides the U. affinis female U. affinis female
Finding of host Visual aspect of stem, Flying adults of plant branches and stalks of the U. affinis are panicle. (Effect of attracted and land olfactory stimuli not on the panicle checked).
Finding of ovi- Spatial arrangement and Upward directed position substrate direction of the branches, movement leads especially•the angle formed U. affinis to by the branches and the flower-buds vertical line. . (Effect of "guiding 'rail")
External examination -Size and shape of closed Walking over the of oviposition sub• ,flowerbuds (visual aspect and flower-bud which strate mechanically-tactile proper• may'. be touched with ties proboscis or point of ovipositor sheath Of secondary importance: Apical ruggedness of bud Attempts at probing brought about by structure (i.e. at intro• of external bracts. Visual ducing ovipositor pattern formed by external into the substrate bracts (Of minor or no importance: chemical properties of the surface of the bud)
Internal examination Thickness and hardness of the Perforation of the of oviposition sub• cover of the flower-bud (i.e. cover of the flower strate of middle and upper bracts) bud if the mechanical resistance of the cover can be overcome. Internal structure- of the Probing by means of cavity of the flower-bud ^ the apical part of ovipositor. Internal dimensions, probably Deposition of eggs mainly size of the undeveloped tubular florets
Source: Zwolfer (1970) TABLE XXVII. Length of ovipositor, and dimensions of oviposition site of some Urophora sp.
Length of the Length of the Urophora sp. Host plant closed head ovipositor of the host attacking host
U. affinis Jrfld Centaurea, diffusa, 4 (3)- 8 mm 4.5- -5.8 mm (1.7 mm)"- C. maculosa~
U. siruna-seva Hg. C. solstitialis 4-12 mm 5.0- 6.5 mm (1.9 mm)
U. sp. nr solstitialis L. Carthamus lanatus (origin southern France) (wild safflower) 18-25 mm 10.0-12.5 mm (3.8 mm)
Urophora, undescribed Cynara cardunculus 35-45 mm 12.5-18.0 mm (4.9 mm) sp. from southern Italy (wild form)
^Values in parentheses: Average length of ovipositor sheath for 10 individual females
Source: ZwOlfer (1970) 65
of different ecotypes within the species of U. affinis it can be assumed that the host pattern of the population associated with C. maculosa is sufficiently stable to warrant introduction to North America".
Urophora affinis adults were released in the Kamloops region in the summer of 1970 under the direction of Dr. Peter Harris and with the co-operation of William Hubbard. U. affinis populations were released in Centaurea maculosa and in C. diffusa plant communities. Hubbard's (41) preliminary results indicated that approximately 3% of the C. maculosa,heads were attacked, but only 0.1% of the C. diffusa heads were attacked (Table XXVIII). The reason for the relatively low proportion of C. diffusa heads attacked may be due to the smaller flower buds of C. diffusa as compared to those of C_. maculosa. . Sweeps of the two release sites in the spring of 1971 indicated that the fly was capable of surviving the winter conditions in the Kamloops area. Additional releases of U. affinis were conducted in'the spring and early summer of 1971. Dr. Peter Harris (36) has-determined that the U. affinis populations on C. diffusa and. C_. maculosa are increasing at the rate of approximately ten fold per year during the first two years since their release in the Kamloops region.
Another promising insect for the biological control of Centaurea spp. in British Columbia, Metzneria paucipunctella Zel., has been extensively studied by Englert.(21). Englert suggests that "it is the most effective of the insects associated with the flowers of C. stoebe, a single larva being capable of destroying 95% of all viable achenes". M. paucipunctella larvae do compete with U. affinis larvae and will kill and feed on them if"they come in contact with the. U. affinis larvae. 66
TABLE XXVIII. Urophora affinis,attack of Centaurea at B.C. release sites 2 (M m plots sampled in the four cardinal directions)
Distance from Average % Attack release point of heads Ipaces; .
Fall, 1971. Chase 0 3.80 (C. maculosa) 10 0.20 20 0.00 50 0.07 Walachin 0 4.70 (C. maculosa) 10 0.70 20 0.13 50 0.10
Pritchard 0 0.46 (C. diffusa).. 10 1.69 20 0.00 50 0.24
Fall, 1970.
Walachin 0 2.72 (C. maculosa) 5 1.94 10 2.42 20 0.32
Pritchard 0 0.36 (C. diffusa) 5 0.00 10 0.00 20 0.06
Source: Harris.(1971) Populations of M. paucipunctella will be released in the summer of 1972 at a site somewhat isolated from the Urophora release sites in the Kamloops region.
The use of plant pathogens as biological weed control agents has been recently reviewed by Wilson (96). The role.of plant pathogens in reducing plant populations is well understood, but plant pathologists, have devoted little attention to diseases of weeds. Wilson indicated the need for co-operation between workers in biological control, usually entomologists, and plant pathologists. The potential damage of plant pathogens has been demonstrated by such devastating diseases as the Dutch elm disease and the late blight of potato.
Recently Inman (47) stated: "There is a distinct possibility that certain selected plant pathogens may have sufficient pathogenicity on specific weeds to be of value as biological agents". He has been studying the potential of a macrocyclic heteroecious rust., Lromyces rumicis (Schum) Wint.., as a biocontrol agent of Rumex species. ]hman suggests that U. rumicis has shown sufficient potential to warrant introduction into North America for further trials as a biological agent
for curly dock.
Dr. Peter Harris (35) has obtained a culture of Puccinia
centaureae, an autoecious rust, from eastern Europe to study as a potential biocontrol agent for the Centaurea species in Canada. However, the culture was not viable on arrival in Canada.. It is hoped that addi• tional material will be available shortly. 68
Guyot (34) indicated that Puccinia jaceae is recorded on C. diffusa in Bulgaria, Romania, Ukraine and Crimea where infection is very heavy. Savile (79) surveyed the Puccinia species attacking Cardueae in Europe and established Puccinia jaceae var. diffusae nov. by utilizing the above collections. Guyot also indicated that C_. maculosa is. a host of P. centaureae-vallesiacae in Bulgaria,- Romania and Russia and a host of P_. jaceae in Switzerland. P_. centaureae var. centaureae was also recorded on Centaurea species closely related to C. diffusa. C. diffusa plants infected with P. jaceae var. jaceae exhibited a resistant reaction and thus careful collection of the variety diffusae .would be of utmost necessity if this organism is to be considered as a potential biological control agent of C. diffusa in British Columbia.
Savile (79) conducted a survey of the native and introduced autoecious Puccinia species in North America. Introduced rusts included P. centaureae var. centaureae which was observed on C_. nigra at Indian Point, Nova Scotia, in July of 1965 by D.B.O. Savile. The rust was located in only one colony even though the weed was locally common (79). P. acroptili was recorded on Centaurea repens near Midway, British Columbia. Savile, in regard to biological control of 9_. repens, suggests "It might be worth seeking the importation of other biotypes for establishing-a degree of biological control of the host. The mor• phological distinctness of the rust strongly indicates that it is strictly host-limited".
Numerous authors (3,46,86) suggests that the ideal method of weed control is the combination of cultural, mechanical, herbicidal, and biological control which will maintain the environment as detrimental to the weed as possible. Ryerson and Sonder (76) utilized a herbicide band treatment as a means of seedbed preparation when studying the feasibility of seeding desirable grasses onto range densely infested with spotted knapweed. They found that the establishment of thick- spike wheatgrass (Agropyron dasystachyurn) in all herbicide banded strips was rated poor. They suggested that the poor establishment of the seeded wheatgrass was primarily due to competition from existing perennial grasses.. Where perennial grasses were absent,, establishment of the wheatgrass was good to excellent. They did not suggest that herbicide damage might have resulted in poor establishment of the wheatgrass.
Recent studies by Scifres and Halifax (80) have shown that picloram adversely affects the rate of grass seedling establishment when applied to reseeded range or range in poor condition. Hubbard's (40) study also reveals that picloram retards grass establishment. Hubbard's integrated approach demonstrates, the benefits of combining herbicide treatment, reseeding, and protection from grazing on the control of C. diffusa in the dry interior of British Columbia. 70
B. Experimental Methods
A soil disturbance study was conducted to determine the effect of simulated cultivation on the population of C. diffusa. Two rangeland sites were chosen near Kamloops, B.C. The treatments were: one disturbance in the spring, two disturbances (spring and summer) and control. One meter square plots were set up in a randomized complete block design with three replications. The treatments were carried out with a shovel to simulate cultivation to a depth of approximately 10 cm. Near the end of the summer the number of plants anchored to the soil were recorded and seed was collected from plants which produced seed in each of the plots. Percent germination of the seed collected was determined by placing the seed (25 per dish) on moistened, sterilized- No. 1 Whatman filter paper in glass petri dishes. The dishes were placed in a Seedburg germinator at 25°C. Data were analyzed by the analysis of variance.
Studies were conducted to determine the effect of mowing on C. diffusa and C. maculosa. Rangeland sites at Summerland and Vernon, and Mara and Salmon River, were chosen for C. diffusa and C. maculosa respectively. Four treatments: mowing at bud stage, mowing at flowering, two mowings (bud and flower-stages) and a control were established in a randomized complete block design with three replications of each treatment at each of the two sites for each species. The meter square quadrats were mowed by hand with a small scythe to a height of 2 cm. Near the end of August the plots were observed and the number of seed producers still anchored to the soil were recorded. 71
Seed was collected from all plants which had produced seeds. Percent germination of the seed collected was determined by placing the seed (25 per dish) on moistened, sterilized No. 1 Whatman filter paper.in glass petri dishes. Data were analyzed by the analysis of variance.
Long range studies were set up in 1971 to determine the level of seed destruction required to reduce C. diffusa and C. maculosa to economic levels of infestation. The experiment was set up in-a randomized complete block design with three replications of ten treatments. The treatments were control, 10, 25, 40, 50, 60, 70, .80, 90 and 100% removal of seeds produced. No results have been obtained as data collection will.begin in 1972. .
Herbicide trials established in 1966 and 1967 on C. diffusa and £• maculosa were scored in 1968, 1970 and 1971. The cover of knapweed on the plots was rated from 0 to 5 and the average of the replications of each treatment was calculated. C. Results and Discussion
TABLE XXIX. Effects of soil disturbance on C_. diffusa populations
Number of Plants/m „ . Treatment = = • : : Percent Mature Rosettes Seedlings Total Germ.
1. one dist. 3.00a5- 10.67a 4.67 18.33 97.17a 2. two dist. 0.00a 0.00 0.00a 0.00 0.0.0 3. • control 16.17 14.17a 1.17a 31.50 97.83a
'''means in the same column sharing the same letter do not differ signifi• cantly at the 5 % level according to Duncan's New Multiple Range Test.
The data shown in Table XXIX indicate? that .two relatively shallow cultivations, one in early May and one in early August, will control . the population of C_. diffusa and prevent seed production. A single, relatively shallow cultivation, in the early spring does significantly reduce the number of plants which reach maturity. However, the one cultivation has no effect on the number of rosettes, indicating the ability of the rosettes to regenerate and continue growth. One shallow cultivation apparently brings viable seeds to the surface which germinate and produce a significant increase in the number of seedlings.
C. diffusa and C. maculosa are not commonly found in irrigated pastures or irrigated hay fields. It is possible, therefore, that any range areas infested with knapweeds might be effectively controlled if irrigation could be applied to these areas. Most rangelands produce 73
marginal returns however, and expensive irrigation systems are not
commonly employed over vast acres of dryland range.
The application.of fertilizer to dense infestations of knapweed would have only adverse effects on potential control of the weed. Fertilizer enhances the growth of Centaurea species (Table XXX).
TABLE XXX. Shallow plowing with later fertilizer application (10T fresh horse manure/hectare) (% cover)
Just before Control Treatment Treatment 1955 1956 1957 1958 1955 1956 1957 1958
Grasses 14. 2' 15.1 17.1 6.5 21.5 10.6 10.1 10.6 Legume 0 0.3 0.1 0 0 1.2 0.-9 0.1 Herbage 29.4 28.3 32.3 28.9 24.2 18.5 19.3 6.4 Knapweed 56.4 56.3 50.5 64.6 54.3 69.7 69.7 82.9
Source: Popova (1960)
However, rangeland in good condition responds favourably to fertili•
zers and their application is important in maintaining the competitive
ability of the grasses and other desirable species.
Mowing is a.management practise commonly used to reduce the seed production of weeds. The rosette habit of Centaurea species provides a means by which' it can escape the effects of mowing, but this does not apply to the bolting and fruiting, stages.
The results of the mowing trials (Table XXXI) indicate a signifi•
cant reduction in the number of plants which produced seeds in all 74
TABLE XXXI. The effects of mowing on knapweed
m. , . ' Number of 0 n . • Treatments seed, producer, • s % Germination
1 mowing (bud stage) 7. 83a* 48. 00b 1 mowing (flower stage) 0. 25a 17. 92a
2 mowings (bud and flower stages,) 1. 17a 19. 92a Control 34. 33 91. 08b
"means in. the same column sharing the same letter do not differ significantly at the 5% level according to Duncan's New Multiple Range Test. treatments and the percent germination was significantly reduced by treatments two and three when compared to the control. There was no significant difference between the two species in these studies. Therefore Table XXXI consists of the combined means of both Centaurea species.
C. diffusa seed which was obtained from an area which had been burned by a forest fire in mid August of 1971 was not viable. These observations suggest that burning could be a useful control measure against the Centaurea species in British Columbia. However, due to the disadvantages associated with burning such as the difficulty in achieving a uniform burn and the control of the fire, its potential use as a means of controlling knapweed infestations is limited.
Good management practises for native range are not costly procedures and are often not thought of as an annual expense by many 75. ranchers. Young (102) has suggested a cost of $12.00 to $15.00 per acre for the complete development of a management unit for range improvement including: plowing, seeding, water development, fencing, non use and interest on investment. . However, these costs are generally spread over a number of years and consequently are not a heavy burden to the rancher.
The major limiting factor in the use of cultural control methods for rangeland is the difficulty with rough terrain. Much of the area cannot be traversed by common farm implements.
Through a co-operative effort of the British Columbia Departments of Agriculture, Forestry, and Highways and the Department of Plant Science, University of British Columbia, a knapweed control program was conducted in 1970 and 1971 in the East Kootenay region of British Columbia. The herbicide, picloram, applied to infestations of knapweed in 1970 gave excellent results with minimum need for re- treatment of 'fringe' areas in 1971. Table XXXII illustrates the acres infested with Centaurea species which were treated with picloram in the East Kootenay region of British Columbia.
TABLE XXXII. Results of the East Kootenay Knapweed Control Control Program 1970-1971
Acres treated Species Rate CLb ai/a) 1970. 1971* Total
C. repens 1.5 27 4 . 31 C. diffusa and C. maculosa:, 0.5 194 58.8 252.8 C. nigra 0.5 100 sq. ft. 100 sq. ft.
* acreage does not include small ' fringe'. areas around plots treated in 1970 which were retreated in 1971. 76
It is hoped that this program has controlled the Centaurea species in the East Kootenay region and will prevent vast acreages of rangeland from becoming infested with these troublesome aggressive knapweed.species.
The Department of highways in the Kamloops, the Cache Creek and the Okanagan' Valley regions have begun to use picloram in their road• side spraying programs to control such troublesome weeds as leafy spurge and the knapweed species along road rights-of-way. A program to control C. diffusa on the Research Station at Summerland was initia- : ted in 1971.. Similarly, cseveralvo.r concerned ranchers have also- initiated spraying programs with picloram to attempt,to control the • spread of knapweed infestation.
The rather high cost of picloram, $53.50 per gallon with 2.4 lb. active ingredient or approximately $10.70 -per acre, has greatly limited its potential use in controlling the Centaurea species in the interior of British Columbia-. The returns per. acre would need to be sufficiently high before applications of this expensive chemical over extensive areas of semi-arid rangeland were initiated. The returns per acre of dry-land' ranges are marginal and do not generally warrant application of picloram to control the knapweed species. Costs can be substantially reduced with the use of airplanes when large acreages are treated. However, the application of such a phytoxic chemical over vast areas of semi-arid
rangeland could cause considerable damage. Undoubtedly, numerous forbs,..-; susceptible to picloram, would become endangered species If broad appli• cation of the herbicide was employed. The relatively long persistence of picloram in the soil and its phytoxic effects on such forage crops 77
as alfalfa has further limited its use in areas which may be placed in forage production in the near future.
The herbicide, picloram, does provide encouragement in the control of the knapweed species in the interior of British Columbia, especially along roadsides and scattered infestations. . However, due to its high costs and possible adverse ecological effects, the major infestations cannot be economically controlled using herbicides. The perimeter areas of the knapweed infestations may be effectively controlled and the spread of knapweed infestations can be restrained with the effective use of herbicides.
In the late spring of 1971rthe author observed a number of C. diffusa plants in the bolted stage which appeared wilted and eventually died before seed production. The affected plants were located in a rangeland infestation east of Vernon, British Columbia. Close examination of the affected plants indicated considerable swelling at the crown region of the tap root. Dissection of the roots of affected plants revealed a black sclerotium-like body (Figure 13). Numerous other sclerotia were observed on and just beneath the root epidermis of affected plants.
Two fungal organisms were consistently isolated from the diseased plant material.
Before identification of the fungus which produced the sclerotia could be attempted the dormancy of the sclerotia had to be broken. The breaking of the sclerotia dormancy and subsequent production of apothecia was accomplished by placing the sclerotia, growing on sterilized potato dextrose agar, into cold treatments of 4°C, 0°C or -24°C for periods of one or two months. The treated sclerotia were then placed in sterilized 78
moist greenhouse, soil.
The Koch-postulates as described by Barnes (7) were carried out with the two fungal isolates;
Table. XXXIII" indicates that apothecia were formed from sclerotia receiving the 4°C and 0°C treatments but not from those receiving the
-24°C treatments (Figure 14). Cultures of the sclerotia and apothecia with ascospores were identified by M."E. Elliott as Sclerotinia
sclerotiorum (Lib.) de Bary (20) (Figure 15). iiiiniiuiiiiiiim
0NV19M3 Ni 3uvi^
Fig. 14. Apothecia produced from cold treated sclerotia
Fig. 15. Plate culture of S_. sclerotiorium 80
TABLE XXXIII. . Treatments utilized to break sclerotia dormancy
Min. time for apothecia Temperature Treatment Duration to appear after being placed in the soil
1 month none formed >2 months none formed 1 month 98 days 2 months 46 days 1 month 33 days 2 months 68 days
The fungal organism .which was concomitantly isolated from the diseased plant material with S_. sclerotiorum has been identified as a new species, Microsphaeropsis centaurea^Morgan-Jones sp. nov. (in.ed.)
(68) (Figure 16).
Table XXIV illustrates the results of following Koch's postulates with S_. sclerotiorum and M. centaureaeon C. diffusa and C. maculosa.
One possible means of natural spread of the disease organisms may be due to a root coccid, Phenacoccus sp. nr. solani Ferris, which were collected from the roots of a number of C_. diffusa and C. maculosa plants in the dry interior of British Columbia. The root coccid was identified by W.R. Richards (73).
The wilt fungus, Sclerotinia sclerotiorum, is widely distributed and causes considerable damage to vegetable crops such as beans, lettuce and celery. Conners (14) lists S_. sclerotiorum as pathogenic on such Fig. 16. Plate culture of M. centaureae TABLE XXXIV. Determination of pathogenicity of Sclerotinia sclerotiorum and Microsphaeropsis centaureae on Centaurea diffusa.and C. maculosa
Disease Fungus Method of inoculation Organism Host material Symptoms Produced Re-isolation
S_. sclerotiorum Mature C. maculosa sterile hyphae wilted + Rosette C. maculosa suspension to soil + Mature C. diffusa . plus wounding of host wilted sclerotia root material in root Rosette C. diffusa
S. sclerotiorum Mature C. maculosa sterile hyphae suspension wilted Rosette C. maculosa to soil Mature C. diffusa wilted sclerotia in root Rosette C. diffusa
S_. sclerotiorum. Mature C. maculosa sterile hyphae suspensions plus Rosette C. diffusa of both organisms to soil M. centaureae Mature C. maculosa Rosette C. diffusa
S. sclerotiorum Rosette C. maculosa sterile hyphae suspension wilted (death) + Seedling C. maculosa to leaf surface wilted (death) + Rosette C. diffusa wilted (death) + Seedling C. diffusa wilted (death) + M. centaureae Rosette C_. maculosa sterile spore suspension Seedling C. maculosa sprayed onto leaf "leaf spotting surfaces followed' by death/.'- Rosette C. diffusa Seedling C. diffusa "leaf spotting followed by death.";- CO Leaf spotting symptoms were repeated in a replication of the initial experiment. 83
valuable crops as alfalfa (Medicago sativa L.) and sunflower (Helianthus annus L.). The ubiquitous nature of this plant pathogen and its broad host range decisively limit its potential as a biological control agent of the Centaurea species in the interior of British Columbia.
The'United States Department of Agriculture (2) has listed plant diseases which have been observed on species of the genus Centaurea. Table XXXV lists those diseases observed on Centaurea species other than C. americana, C_. cyanus, C. cineraria and C_. montana.
TABLE XXXV. Plant diseases observed on Centaurea species in North America Organism State Disease
Albugo tragopoyonis . Tex. white-rust
Erysiphe cichorearum Calif. powdery mildew Meloidogyne sp. Ohio root-knot nematode
Phymatotrichum omnivorum .. Tex. root rot Plasmopara halstedii - Iowa . downy mildew
Puccinia cyani Md. and Tex. rust Rhizoctonia solani Tex. root and stem rot
Sclerotinia sclerotiorum Tex. stem rot, wilt Sclerotium rolfsii N.J. southern blight
Yellows (Chlorogenus callistephi) Pa virus
Source: U.S.D.A. Handbook 165 (I960)
Dr. C.G. Shaw "(84) has indicated that there are no additional
records of parasitic or pathogenic fungi on species of the genus • 84
Centaurea. Conners (14) did not list any plant diseases of C. diffusa or C. maculosa in Canada.
The report of S_. sclerotiorum on Centaurea in Texas would not have been observed on C_. diffusa nor C_. maculosa as these species have not been recorded in that state; '
Microsphaeropsis centaureae is pathogenic to juvenile leaves of
C. diffusa and C. maculosa. The fungus produces necrotic lesions and eventual leaf death of infected plants (Figures 17 and 18). Sutton (90) reports Microsphaeropsis. callestra (H. Syd) nov. comb, as parasitic on leaves of Eucalyptus haemastoma:.in Australia. He describes the lesions as follows: "...up to 0.5 cm. diam. , mostly circular but occasionally irregular, sometimes confluent but more frequently separate,- appearance similar on both sides pf the leaf, edge raised, sharply delimited from the healthy tissue by a brown to purplish brown line, surrounded by a diffuse halo of brown to purplish brown discoloration, central lesion tissue cream throughout or brownish towards the periphery". The leaf spots observed on C_. diffusa and C. maculosa infected with M. centaureae. appear very similar to those described by Sutton.
Campbell (11) has reported sclerotia of S_. sclerotiorum as being parasitized by Coniothyrium minitans and indicated the possibilities of biological control of Sclerotinia species by Coniothyrium minitans.
The genus Microsphaeropsis Holm is based on Coniothyrium olivaceum Bon.
(61). This•suggests that M. centaureae may be.parasitic on the sclerotia of S. sclerotiorum. However, it does not explain why both fungal organisms were consistently isolated from all portions of the diseased host material.
Both fungus organisms Care, parasitic .tcTC. 7diffusa "and C. maculosa. Fig. 17. Leaf spot on C. diffusa
Fig. 18. Leaf spot on C_. maculosa 86
The association between these two fungus species requires further study. Also the potential of M. centaureae as a biological agent of Centaurea species in the interior of British Columbia needs to be explored more fully.
The economics of biological control have been reviewed by a number of authors (5,46,86). They have indicated that the annual financial benefit is exceedingly high with costs limited to exploration, research, and introduction of the biological agent. Once control is achieved, no expense or very little recurrent annual expenses are incurred. Hussey
(46) points out "that biological control...is particularly useful and suitable for pest control in situations where costly chemical controls are out of the question". There has been, in the past, a lack of accurate economic information which has lead to considerable criticism of biologi• cal control. Therefore, accurate balance sheets of biocontrol attempts should be maintained to illustrate the benefits of biological control.
The data in Table XXXVI illustrates the order of magnitude of the costs of biological control of a weed and include the approximate number of scientist-years spent on it plus the cost of overseas exploration.
Harris (37) suggested that: "In round figures the cost of biological control of a weed may be as much as $500,000 if it is possible to use agents that have been shown safe and effective elsewhere and twice this sum if it is necessary to do the development work". These costs compare very favourably to those for developing a new herbicide but,as Harris points out, biological control does not have the continued costs of expense and labor once the biocontrol agent becomes self-regulating. 87
TABLE XXXVI. Evaluation of biological control measures against weeds in Canada
5 Weed Start of Prog, Estimated costs ' Degree of in Canada Abroad Canada Success5'"'5
Carduus?;.s"p. 1968 45 20 tt
Cirsium. arvense 1963 45 320 t Euphorbia sp. 1965 25 100 - t Hypericum 1952 10 410 (threat) tttt perforatum (forage) ttt Linaria vulgaris 1957 10 120 t Senecio jacobaea. 1961 10 .220 (forage) ttt (cattle) tttt
* thousands of dollars ** - No control t Slight pest reduction or too early for evaluation. tt Local control, distribution restricted or not fully investigated. ttt Control widespread but local damage occurs tttt Control complete
Source: Harris (1971) Huffaker and Andres (44) state: "where effective, biological
control by introduced natural enemies is cheap, permanent in nature, without need for recurrent expense, and does not add toxic pollutants
to the environment, endangering non-target organisms, plant or animal".
The Centaurea species are common along roads and readily invade misused dryland ranges in the southern interior of British Columbia. Each method of control has its limitations. The use of cultural control such as mowing or cultivation is generally not applicable for knapweed control. Herbicides are'useful management tools , but the high costs of picloram have limited its use over large areas of range- land.. Biological control of the Centaurea species has just recently been initiated and it will be 6 to 10 years before the returns will be appreciated if the biological control agents become sufficiently well established.
Control, by whatever means, does not eliminate the possibility
of a 'resistant' weed replacing the knapweed in the dryland• range
environment. Control methods must be accompanied with appropriate
management.practices in order to maintain vigorous stands of useful
forage.
Proper range management includes moderate grazing of the range to maintain vigorous grass growth and to protect the plant crowns.' Heavy grazing should always be followed by a sufficient rest period to allow depleted food reserves to be built up in the roots of the forage species. Even.distribution of grazing animals is also essential on well managed range (51,57). 89
Fig. 19. Re-establishment of C. diffusa after herbicide treatment at OK Falls, B.C.
5 / 4_
Weed 3- iv / y Density Rating 2- V • (0-5) * y 1-
0_ —I 1 r 1971 1967 1968 1969 1970 Time (yr.)
f time of herbicide application A 2,4-D amine @ 2 lb/a B picloram @ 8 oz/a
Fig. 20. Re-establishment of C. maculosa after herbicide treatment at Chase, B.C.
5
4 -
Weed 3 - Density Rating 2 _ (0-5)
1 - B 0 . T T —J" 1967 1968 1969 —r— 1971 1970 Time (yr.)
^ time of herbicide application A 2,4-D amine @ 2 lb/a B picloram @ 8 oz/a 90
Figures' 19 and 20 illustrate the residual effect of picloram in controlling knapweeds as compared with 2,4—0 amine. The dry OK Falls site is in extremely poor condition. The apparent poor response to the herbicide treatment and relatively rapid re-establishment of C. diffusa is partially due to the lack of grass establishment after the.herbicide treatments.' The Chase site was in better condition prior to herbicide treatment and native grasses were capable of increased production as the competition of C. maculosa was greatly reduced in the picloram treated plots. Grazing was not controlled at either site and as a result of subsequent overgrazing of the treated areas the knapweed species were capable of rapid re-establishment. These studies indicate the need for good management techniques to follow-herbicide treatment of knapweed infested areas.
It can be recommended that control of C. diffusa and C.. maculosa , can be achieved by cultural- methods such as cultivation and irrigation on only those areas that are amenable to extensive cultivation. Herbici- dal control can be utilized to control roadside infestation and to prevent further spread of the knapweed from the perimeter of the existing infestation. The feasibility of biological control is encouraging and the development of phytophagous and pathogenic agents could economically reduce the knapweed infestation in the interior of British Columbia. 91
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APPENDIX TABLE I. Effect of temperature on germination of C. diffusa and C. maculosat
,': Duration of Temperature (°C)tt r % test (days) 7 10 13 16 19 22 25 28 31 34 Linear Quadratic Residual One Oa • Oa Oa Oa 14a 41b 59b . 45b 12a 5a 21.04* 25.75* 53.19 Two (diffusa) Oa Oa 10a 57cd 86e 76.de lOOe 76de 48bc 24ab 18.42 17. 35 64.21 Two (maculosa) Oa Oa 43bc 86e 76de 95e 86e 90e 38bc 5a 14.80* 72.91* 12.28 Two (Av.)• Oa Oa 26bc 71d 81de 86de 93e 83de 43c 14ab 14.80* 72.91* 12.28 Three Oa 26b 74c 88c 88c 91c "95c 86c 50 14ab 3.72* 92.50* 3.77 Four 10a 64bc 81cd 88d 88d 95d 98d 86cd 52b 19a 0.12 92.36* 6.51 Five 21a 76b 91b 88b 88b 95b 98b 86b 55 19a 0.97 88.48* 10.54 Six 24a 81b 91b • 88b 91b 95b 98b 86b 55 24a 1.25 87.20* 11.55 Seven 26a 81b 91b 88b 91b 95b . 98b 86b 55 24a 1.64 87.24* 11.10 Eight 33a 81b 91bc 91bc 91bc 95bc 100c 86bc 55 24a 3.07* 87.24* 9.68 Nine 33a 81b ' 91bc 91bc 91bc 95bc 100c 86bc 55 24a 3.07* 87.24* 9.68 Ten 33a 81b 91b 93b 91b 95b 100b 88b' 55 24a 2.88* 87.30* 9.81
t combined analysis for the two species except for day two when there was a significant (P = 0.05) treatment by species interaction. tt means in the same row sharing the same letter were not significantly different at the 5% level according to Duncan's New Multiple Range Test. 2 *" r which were significant at the 5% level according to Duncan's New Multiple Range Test. ,101
APPENDIX TABLE II. Effect of Sowing Depth on Seedling Emergence of
' £• diffusa, and'C. maculosa
Duration of Test (Days) Species Sowing Sixteen Twenty-Four depths Eight
Diffusa 0 cm 58 80 81 0.5 cm 58 63 62 1 cm 70 68 68 3 cm 3 16 16 5 cm 0 0 0
Maculosa 0 cm 58 90 91 0.5 cm 75 73 73 1 cm 70 78 78 3 cm 17 26 26
5 cm 0 7 8