AMERICAN BLACK NIGHTSHADE (Solanum Americanum MILL.) INTERFERENCE in WATERMELON (Citrullus Lanatus L.)

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AMERICAN BLACK NIGHTSHADE (Solanum americanum MILL.) INTERFERENCE IN WATERMELON (Citrullus lanatus L.)

CELESTE ALINA GILBERT

A THESIS PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE

UNIVERSITY OF FLORIDA

2006

Celeste Alina Gilbert

This thesis is dedicated to my grandmother, Claire K. Gilbert, who inspired me to pursue a degree in science through her love and support.

ACKNOWLEDGMENTS

First and foremost I wish to thank my advisor, Dr. William M. Stall, for all the

help and guidance he has given me throughout my time at the university and

especially throughout the writing process. Without his patience and guidance I

would not have been able to write this thesis. I would also like to thank my

committee members for their assistance and support throughout my program. I

am extremely grateful to Dr. Eric Simonne, whom I consider a mentor and a

friend throughout my time in Gainesville.

For their assistance in the field and with my research I would like to thank

the farm crews at the NFREC and PSREU, especially Berry Tanner and Darrel

Thomas, for their friendships and support. I would also like to thank Aparna

Gazula for both her help with statistics and her wonderful friendship, without

which I would have struggled. For all their wonderful support and kindness I wish

to thank all my friends here in Florida; they have provided me with support and

generosity throughout my time in Gainesville.

Finally, I wish to thank my parents, Donna and John Gilbert, for their interest and underlying support for my research, my brother and sister Chaz and

Carolina Gilbert for their encouragement and love, and my grandmother Claire

Gilbert, whose faith in me has given me strength through the tougher times.

TABLE OF CONTENTS

page

ACKNOWLEDGMENTS ...... iv

LIST OF TABLES ...... viii

LIST OF FIGURES ...... ix

ABSTRACT ...... xi

CHAPTER

1 LITERATURE REVIEW...... 1

Competition...... 1 Economic Impact ...... 2 Designs for Studying Competition in Agriculture...... 3 Additive studies ...... 3 Substitutive studies (replacement series)...... 4 Systematic studies ...... 4 Neighborhood (area of influence) studies...... 5 Review of American Black Nightshade and the Nightshade Complex ...... 5 Origins and Distribution of American Black Nightshade (S. americanum) ...... 6 History ...... 6 Vegetative Characteristics of Solanum Americanum...... 7 Black Nightshade Biology ...... 7 Germination of Black Nightshade Seed...... 8 Temperature...... 8 Other treatments to promote germination...... 9 Osmotic pressure and pH...... 10 Critical Weed-Free Periods and Densities for Nightshade...... 11 Control of Black Nightshade...... 12 Mechanical Control...... 12 Cultural Control...... 12 Chemical Control ...... 14 Biological Control...... 14 Review of Watermelon (Citrullus lanatus) ...... 14 Watermelon Taxonomical Description ...... 14 Watermelon Production in Florida...... 16

Weed Studies in Watermelon ...... 17 Watermelon Nutritional and Cultural Requirements ...... 18 Nutrition ...... 18 pH...... 19 Temperature ...... 20 Mulches and Growth: High and Low Maintenance ...... 21 Mulches...... 21 Plant spacing...... 22 Water and nutrients...... 23 Transplants versus seeded ...... 23

2 SEASON-LONG INTERFERENCE BETWEEN WATERMELON AND AMERICAN BLACK NIGHTSHADE ...... 25

Introduction ...... 25 Objectives ...... 25 Materials and Methods...... 26 Measurable Variables ...... 27 Experimental Design and Statistical Analysis ...... 28 Results ...... 29 2005...... 29 2006...... 30 Nightshade Dry Weight...... 31 PAR...... 31 Plant Measurements...... 32 Discussion...... 32

3 SPATIAL DISTANCE STUDY BETWEEN AMERICAN BLACK NIGHTSHADE (Solanum americanum Mill.) AND WATERMELON (Citrullus lanatus L.) ...... 46

Objective ...... 46 Materials and Methods ...... 46 Measurable Variables ...... 47 Experimental Design and Statistical Analysis ...... 48 Results and Discussion...... 48

4 SEED GERMINATION TRIALS USING AMERICAN BLACK NIGHTSHADE SEED...... 51

Objectives ...... 51 Material and Methods...... 51 Bleach treatment ...... 52 Pre-germination treatment...... 52 Germination trials ...... 52 Statistical Analysis...... 53 Results ...... 53

Trial 1: September 8-22, 2005 ...... 54 Trial 2: November 3-17, 2005 ...... 54 Trial 3: January 29- Febuary 12, 2006...... 55 Discussion...... 55

5 SUMMARY AND CONCLUSIONS ...... 59

APPENDIX

ENVIRONMENTAL CONDITIONS FOR EACH YEAR AND SITE...... 62

REFERENCES...... 63

BIOGRAPHICAL SKETCH ...... 70

vii

LIST OF TABLES

Table page

3-1 Treatment effects on watermelon yields as percent of control. Treatments are spacing from watermelon plants...... 50

4-1 Germination percentages of American black nightshade seed by days: September 8-22nd 2005...... 57

4-2 Germination percentages of American black nightshade seed by days: November 3rd-17th 2005...... 57

4-3 Germination percentages of American black nightshade seed by days: January 29th-Febuary 12th 2006...... 58

4-4 Germination percentages of American black nightshade seed for each trial by 14...... 58

A-1 Environmental conditions for the North Florida Research and Education Center (NFREC) 2005...... 62

A-2 Environmental conditions for the North Florida Research and Education Center (NFREC) 2006...... 62

A-3 Environmental conditions for the Plant Science Research and Education Unit (PSREU) 2006...... 62

viii

LIST OF FIGURES

Figure page

2-1 Yields of watermelon fruit 2005 as affected by season-long interference at different SOLAM densities on mulch. The model is Y=a0 * x/(1 + a0 * x/a1), where a0 = 235 and a1=100...... 36

2-2 Number of watermelon fruit as affected by season-long interference at different SOLAM densities. The model is Y = a0 *x/(1 + a0 * x/a1), where a0 = 146 and a1 =100...... 36

2-3 Yields of marketable watermelon fruit 2006 as affected by season-long interference at different SOLAM densities (non-mulched). The model is Y = a0 *x/(1 + a0 * x/a1), where a0 = 115 and a1 =100...... 37

2-4 Yields of marketable watermelon fruit 2006 as affected by season-long interference at different SOLAM densities (mulched). The model is Y = a0 *x/(1 + a0 * x/a1), where a0 = 60.2917 and a1 =100...... 37

2-5 Total number of marketable watermelon fruit as affected by season-long interference at different SOLAM densities (non-mulched). The model is Y = a0 *x/(1 + a0 * x/a1), where a0 = 83.0159 and a1 = 100...... 38

2-6 Total number of marketable watermelon fruit as affected by season-long interference at different SOLAM densities (mulched). The model is Y = a0 *x/(1 + a0 * x/a1), where a0 = 47.8918 and a1 = 100...... 38

2-7 Total yields of watermelon fruit as affected by season-long interference at different SOLAM densities (non-mulched). Model is Y = a0 *x/(1 + a0 * x/a1), where a0 = 73.2858 and a1 =93.6802...... 39

2-8 Total yields of watermelon fruit as affected by season-long interference at different SOLAM densities (mulched). The Model is Y = a0 *x/(1 + a0 * x/a1), where a0 = 35.7464 and a1 =100 ...... 39

2-9 Total number of watermelon fruit as affected by season-long interference at different SOLAM densities (non-mulched). The model is Y = a0 *x/(1 + a0 * x/a1), where a0 = 53.9670 and a1 = 75.6295...... 40

2-10 Total number of watermelon fruit as affected by season-long interference at different SOLAM densities (mulched). The model is Y = a0 *x/(1 + a0 * x/a1), where a0 = 20.2910 and a1 = 100...... 40

2-11 SOLAM dry weight after season-long interference at different SOLAM densities in 2006...... 41

2-12 The level of photosynthetically active radiation (PAR) reaching watermelon vines at the full bloom stage, as affected by season-long interference at different SOLAM densities...... 41

2-13 The level of photosynthetically active radiation (PAR) reaching watermelon vines at the full bloom stage, as affected by season-long interference at different SOLAM densities...... 42

2-14 The length of watermelon vines by SOLAM treatment (mulch): 6, 7 and 8 weeks after planting...... 42

2-15 The length of watermelon vines by SOLAM treatment (non-mulch): 6, 7 and 8 weeks after planting...... 43

2-16 The height of nightshade plants by treatment (mulch) at the NFREC: 6, 7, 8, and 9 weeks after planting...... 43

2-17 The height of nightshade plants by treatment (non-mulch) at the NFREC: 6, 7, 8, and 9 Weeks after Planting...... 44

2-18 The height of nightshade plants by treatment (mulch) at the PSREU: 6, 7, and 9 weeks after planting...... 44

2-19 The height of nightshade plants by treatment (non-mulch) at the PSREU:6, 8, and 9 weeks after planting...... 45

Abstract of Thesis Presented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Master of Science

AMERICAN BLACK NIGHTSHADE (Solanum americanum MILL.) INTERFERENCE IN WATERMELON (Citrullus lanatus L.) By

Celeste Alina Gilbert

August 2006

Chair: William M. Stall Major Department: Horticultural Sciences

Florida is one of the top three producers of watermelon in the US.

American black nightshade is a problematic weed in growers’ fields, yet no research has been done to asses its effects on watermelon yields. Currently, there are no herbicides labeled for use in watermelon to control American black nightshade in watermelon production.

Field trials were conducted in the spring of 2005 and the spring of 2006 to

investigate the interference between American black nightshade (Solanum

americanum) and watermelon (Citrullus lanatus) in both mulched and non-

mulched trials. Watermelon was highly susceptible to negative interference by

nightshade. Watermelon yields reached their biological polyethylene threshold at

two nightshade plants per/m2. At this density marketable yields were reduced by

over 50% in both mulched and non-mulched trials. The highest marketable losses came from the non-mulched trials in both years. In 2006, spatial distance

studies were conducted to examine if distance influenced competition between nightshade and watermelon. Two distances, 15 and 30 cm, were tested at the nightshade density of 2 plants/m2. There was no statistical difference in nightshade growing at either 15 or 30 cm; rather both treatments reduced watermelon yields in a similar manner.

American black nightshade seeds have dormancy mechanisms that prevent germination under unfavorable conditions. These dormancy mechanisms make growing nightshade for experimental research challenging. Germination trials were conducted using American black nightshade seed in 2005 and 2006.

Germination trials tested six combinations of treatments to evaluate which were most effective in producing the highest percentage of germinated seeds. In all trials, the highest percentages of germinated seeds (≥ 89%) came from batches soaked in a 2.7% hypochlorite solution (half strength household bleach) for 30 minuets.

xii CHAPTER 1 LITERATURE REVIEW

Competition

Competition has been defined as a negative interaction between two

organisms (Connell 1990). Definitions of competition are numerous but

essentially they can be divided into two main categories, those that focus on

mechanisms and resource acquisition (Tilman 1982; Grime 2001) and those that

focus on reduction in fitness caused by limited shared resources (Silvertown and

Charlesworth 2001). Within these two definitions competition is again divided

into interspecific, competition between different species, and intraspecific,

competition between individuals of the same species. Connell (1983) theorized

that increasing a species ability to compete interspecifically, would in turn expand

its niche, while increasing intraspecific competition should reduce niche size.

Crop-weed competition studies give greater emphasis to interspecific than intraspecific competition. These studies are designed to identify and highlight the

process of acquisition and pre-emption of resources by the species involved

(Park et al. 2003). Usually the species best suited for the environment has the competitive advantage. Another term used in weed studies for competition is interference within which there are two types, direct and indirect. Direct interference includes the competition between plant species for nutrients, light, water, and space; while indirect interference includes the production of allelopathic chemicals, or the harboring of insect pests and diseases by species,

1 2 which then can be transferred to other species. The effects of competition are not easily proven in nature; however, in agricultural systems where monoculture is in practice, the effects are more visible. Within agricultural systems, cultural practices are implemented to minimize the effects of pests and disease, while maximizing crop yields. It is within these settings that research findings can be implemented to minimize the economic impact weeds have on crop production.

Economic Impact

The economic impact of competition by weeds is examined in two areas, intensity and timing of competition. Intensity is commonly referred to as the density or the number of weeds per unit area that can cause reductions in yields.

Timing of competition refers to the impact competition has upon the crop during critical times of a crop’s growth and production (Radosevich 1987). The terms critical density and biological threshold incorporate both intensity of competition and time of competition within their definitions. The critical density is the highest density of weeds that will allow for maximum crop yields; whereas biological threshold refers to the maximum crop yield loss under current cultural practices

(Cousens 1991; Radosevich 1987). Both critical density and the biological threshold are crop and weed specific. To determine both the critical density and biological threshold an economic threshold is identified for each crop. The economic threshold refers to the point at which yield loss caused by weeds and other pests exceeds the cost of control (Mumford and Norton 1984; Weaver et al.

1992; Zadoks 1985). 3 the economic threshold, control practices will not increase crop yields, while controlling weeds above the threshold can result in profits from higher yields (Garrett and Dixon 1998). Besides measuring density,

3 observing weed spatial pattern may be important in characterizing weed patterns for predicting yields. The more aggregated weeds are, the less overall yield loss is predicted as compared to when they are systematically distributed in the fields

(Garrett and Dixon 1998).

Designs for Studying Competition in Agriculture

There are four commonly applied designs to study weed competition; these are additive, substitutive, systematic, and neighborhood (area of influence) studies (Oliver 1988; Radosevich 1987). Each study has specific objectives, with additive and substitutive studies being the most utilized (Rejmanek et al. 1989).

Additive studies

Additive studies are used to identify weed species effects on a crop under current cultural practices. In additive studies, weed and crop density and proportions are varied. The most common application of additive studies is called “partial additive design” in which one species (often the crop) density remains constant while the other species (often the weed) density is varied

(Radosevich 1987). Additive studies identify the critical density and biological threshold of the crop and weed. The advantages are that the results are directly applicable to the grower’s practices, they can be conducted under the grower’s field conditions, the weed densities are known, and they are an accurate way to evaluate the effects of competition duration of competition and full-season competition (Radosevich 1987). A disadvantage of additive studies is that the specific relationship between the crop and weed is difficult to determine

(Radosevich 1987).

Substitutive studies (replacement series)

In a substitutive study, the total plant density remains constant while the

proportions of weeds to crop are varied. Pure stands of both species are used as controls (Radosevich 1987). The goal of a substitutive study is to determine the yields of weeds and crops in mixtures, as compared to in a monoculture system. The advantages are that they work well in greenhouse settings, they can determine weed competitiveness and they are useful in making models.

They are also excellent in evaluating specific parameters of competition. Despite all the advantages, these studies are difficult to conduct in a field setting, and the results are difficult to apply directly in growers fields (Park et al. 2003;

Radosevich 1987). There are four possible outcomes from substitutive studies.

The first is, no interaction between crop and weeds, thus neither weed nor crop has a loss in yield. The second is, one species is more competitive than the other and contributes more to the total yield. The third is, together neither species produces maximum yields, suggesting that the maximum productivity of species is only achievable with monocultures. Finally, the fourth is that, both species benefit, thus both species produce higher yields together than in a monoculture. This suggests symbiosis, but can also indicate that neither species is able to harm each other as much as expected.

Systematic studies

Systematic studies account for density and proportion together. There are two designs within this group, both of which are combinations of replacement and additive studies. Both studies attempt to characterize competition through weed and crop density and proportion. The first design is an addition series; best

described as a group of replacement series designs. Density and proportion are

varied within this design and thus there are various proportions and densities in each replication. The second design consists of a multiple additive design consisting of different densities of weeds to crops. While both designs have similarities, they differ in that the additive series is set up as a factorial experiment. By designing the additive series as a factorial experiment, the researcher is able to examine all possible combinations of the treatments densities (Cousens 1991; Radosevich 1987).

Neighborhood (area of influence) studies

The neighborhood design for analyzing plant competition was created by

Mack and Harper (1977) in an effort to identify the relationship of one species to the density of neighborhood species within a specific area (Park et al. 2003).

Within the context of weed competition in neighborhood designs, researchers examine the distance and density of weed to crop species to determine the necessary distance and density in order to reach maximum crop yields. The advantages of neighborhood studies include: utility for determining the influence of a singe weed in competition and applicability for computer modeling; and use for obtaining growth and development data on both crop plants and weed species. Disadvantages include: weeds vary in how well they can compete with other plants therefore looking at many different weed species can obscure one species’ significance and they are difficult to establish in field settings.

Review of American Black Nightshade and the Nightshade Complex

The nightshades consists of a complex group of mainly herbaceous to shrubby plants that still remain unresolved taxonomically (Defelice 2003). Prior

6 to 1980 most references to black nightshade referred only to the type species,

Solanum nigrum L. Since then taxonomists have recognized many other species within this complex (Defelice 2003). Within the United States there are four black nightshade species, eastern black nightshade (S. ptycanthum), American black nightshade (S. americanum), hairy black nightshade (S. sarrachoides) and black nightshade (S. nigrum) (Defelice 2003). These species are commonly referred to as the “Solanum nigrum complex” or the black nightshade complex (Defelice

2003). Deciphering the taxonomic relationships of the black nightshade complex has proven a difficult task as they share a similar morphology, have high phenotypic plasticity, and high genetic variability (Defelice 2003).

Origins and Distribution of American Black Nightshade (S. americanum)

Solanum americanum is the most unrelated of the species within the complex with only 43% genetic similarity (Dehmer and Hammer 2004). American black nightshade is native to the Americas, particularly Cuba and South America

(Dehmer and Hammer 2004; Olet et al. 2005). In the Americas it is found mainly in the southern coastal states all the way to California and into Mexico, Central

America and South America (Ogg Jr. et al. 1981).

History

The history of black nightshade dates back to the Paleolithic or Mesolithic age, suggesting they may have been established before the agricultural activities of Neolithic man (Defelice 2003). They are known as a problematic weeds in 61 countries and in more than 31 crops (Defelice 2003). In North America, the black nightshades have become more problematic over the last 50 years as the removal of competitive grasses and broadleaf weeds by herbicides has favored

the growth of more difficult to control weeds such as those in the nightshade

complex.

Vegetative Characteristics of Solanum Americanum

Ogg jr. et al. (1981), did an extensive anatomical comparison of the

nightshade complex and botanical descriptions. They found and found there are

few consistent structures used to identify the nightshade to species. Flower and

fruit structures are the most dependable while vegetative structures are generally

inconsistent. S. americanum is often found in the form of an erect annual to short-lived perennial herb growing up to 1.2 m in height. Stems are mostly herbaceous and slender but can become woody with age. Each fruit can contain

50-110 white seeds varying in size from 1.4 to 1.8 mm in length. All nightshade species have a fibrous root system and a shallow taproot (Ogg Jr. et al. 1981).

Black Nightshade Biology

American black nightshade reproduces sexually with and without pollinators, although they are primarily self-pollinated (Defelice 2003). The pollen of nightshades is distributed by the vibration of the wings of bees visiting the flowers (Bassett and Munro 1985). Flowering is both light and temperature dependent (Keeley and Thullen 1983). Plants germinating March through June flower in 7 to 9 weeks, whereas plants germinating July thru September flower in only 5 to 6 weeks (Keeley and Thullen 1983). In a germination study, Keeley and

Thullen (1983) found that plants germinating during the months of April through

July produced an average of 1000 berries per plant with 8,000 to 30,000 seeds per plant with an average of 60 seed per berry. The high production of seeds

during these months coincide with crop planting and there for can cause problems within crops.

Germination of Black Nightshade Seed

Black nightshade has certain dormancy mechanisms that prevent its germination except under favorable conditions. To determine the precise conditions necessary, studies have attempted to isolate each variable, and their effects on seed germination. Diurnal fluctuations in temperature are necessary for many seeds either in the initiation or in the acceleration of the germination process. Initiation is a two part process, first the unearthing of the seed and the triggering of germination by exposure to light and second, a diurnal flux in

temperature from being unearthed (Thompson et al. 1977). Nightshade

emergence occurs in late March though April, at which time 90% of viable

seedlings emerge, with few to almost no seedling emerging after June (Ogg Jr. and Dawson 1984). During these months, nightshade species are assisted in their germation by shallow tillage. Givelberg and Horowitz (1984) found freshly

ripened seed did not exhibit any dormancy, but soon after ripening it developed a

periodicity of dormancy that lasted throughout the winter months. They also

found the percentage of viable seed in the seed bank decreases over time but

the time the seed remained viable depended on the conditions present at the

time of the fruit ripening (Givelberg and Horowitz 1984).

Temperature

Wagenvoort and Van-opstal (1979) compared alternating temperatures with

constant combined photoperiod manipulation (with and without light). In both the light and dark, they found alternating temperature produced more germinating

seed than under constant temperatures (Wagenvoort and Van-opstal 1979).

Thomson and Witt (1987) found under light conditions, a constant temperature of

30 oC was as good as alternating temperatures. However, under dark conditions

alternating temperatures between 10/30 and 20/30 oC produced the highest

percentages of germinating seed. Zhou et al. (2005) found that germination was

optimal when seeds were exposed to constant temperatures in the range of 28oC to 33°C or with alternating temperatures of 30/25°C and 35/30°C. Under light conditions germination occurred only when temperatures were 20°C or greater, while in the dark, germination was altogether poor except when temperatures were alternated between 30/25oC and between 35/30oC. Under suboptimal

temperatures (< 20oC), seed germination was enhanced by a short exposure to

light, while long exposure inhibited it (Zhou et al. 2005). Roberts and Lockett

(1977) found that alternating temperatures of 10/25 oC, 10/30 oC and 20/30 oC or constant temperatures of 25 oC and 30 oC produced the best results for Solanum

dulcamara L. seed germination; while temperatures of 20 oC or less, produced no

germination. These results suggest that constant temperatures of 30 oC or

greater or alternate temperatures produce high percentages of germinating seed

under light conditions. Under dark conditions, seed germination has more

stringent temperature requirements. While constant temperatures of less than 20 oC are non conducive to seed germination.

Other treatments to promote germination

Wagenvoort and Van opstal (1979) examined different treatments in an

effort to improve germination of nightshade seed: rinsing, stratification, and the

application of fertilizer. Rinsing involved the soaking of seeds for a period of 12

10 hours in tap water changed 3 times during the treatment. They found rinsing had no notable effects on germination. Stratification for 1 week alone at 5°C did not appear to increase seed germination; while in combination with alternating temperatures (25/9 oC) during or the application of fertilizer thereafter, improved

germination. Stratification for over 1 week did not appear to increase germination (Wagenvoort and Van opstal 1979). They concluded that with hard

to germinate seeds, such as black nightshade, the combinations of treatments

are most effective in improving germination. Givelberg and Horowitz (1984) found that under dark conditions dormancy could be overcome by 100% O2 at

temperatures below 45 oC, or by the addition of gibberellins. Another study by

Roberts and Lockett (1977) found almost 100% germination at temperatures of

20oC and higher when seeds were imbibed with 300 ppm of a mixture of gibberellins A4 and A7. Barnea et al. (1990) examined the effects of bird ingestion on seed coat and seed germination. They found that ingestion had no effect on the seed coat or on with germination.

Osmotic pressure and pH

Thomson and Witt (1987), found that osmotic stress decreased germination from 68% to 55%, while Givelberg and Horowitz (1984) found that the initial water intake was not as critical as water intake over time. Thomson and

Witt (1987) the optimum pH for germination was found to be within the range of

5-8, while below the pH of 5, seed vigor was affected.

Critical Weed-Free Periods and Densities for Nightshade

There have been many studies identifying critical weed free periods and

critical densities for nightshade in combination with crops. Previous studies on

crop yield loss from nightshade competition have shown nightshade to be a

strong competitor with crops. Weaver et al. (1987) reported that four nightshade

plants per m2 could reduce yields 25 to 60% in transplanted and up to 80% in

direct seeded tomatoes. Agamalian (1983) found that only three nightshade

plants/m2 reduced broccoli yields by 33% and eight nightshade plants reduced

broccoli yields by 50%. Blackshaw (1991) found two hairy nightshade plants/m of

row were enough to significantly reduce bean yields by 13%. He found that a

weed-free period of 9 weeks was required for beans to reach seed weight

comparable to those plants kept weed-free all season long. In contrast,

Fennimore et al. (1984) found bean to be a better competitor than black

nightshade in a replacement series experiment. They found that bean emerged

earlier and was better able to utilize resources than black nightshade. Roos

(1999) found that American black nightshade was a strong competitor with

pepper plants and that the biological threshold for maximum yield loss occurred

at only four nightshade plants/m2. She found that early marketable yields were

most affected by nightshade density; only one nightshade plant/m2 caused a

20% reduction while two plants/m2 caused a 50% reduction in early marketable yields.

Control of Black Nightshade

Weed control can be broken down into four main areas: mechanical,

cultural, chemical, and biological. Effective weed control is often a combination

of these different methods.

Mechanical Control

Mechanical control involves the removal of plant tissue by the use of force.

Mechanical weed control includes methods such as tillage, mowing, hoeing and

hand pulling. In large scale agriculture, hand pulling and hoeing are not practical

because of the high labor costs. When using mechanical means of control such

as tillage, timing is essential. Studies by Ogg Jr. and Dawson (1984) found when

tillage followed seed germination by a few days, it reduced seedling emergence.

However, prior to germination shallow tillage increased the number of emerging

seedlings (Ogg Jr. and Dawson 1984). Research by Reuss et al. (2001) found

that nightshade seed position in the soil matrix was very important in seedling emergence and seed survival. They proposed a no-till system to keep the seeds close to the soil surface and unincorporated in soil aggregate, therefore, limiting

the viability of seeds within the seed bank.

Cultural Control

Cultural control of weeds consists of altering production practices to provide the crop the competitive advantage. Cultural methods include manipulating crop row spacing, timing of planting, use of transplants versus seed, the use of mulches in combination with drip fertigation and soil solarization. The timing of watermelon planting (March and April) in central and north Florida coincides with the emergence of nightshade species. Tillage prior to planting and irrigation

13 during and after planting encourages weed germination and emergence. To limit establishment of the weeds, early-season control is essential. Using transplants for high-value crops such as watermelon may provide a competitive advantage.

Weaver et al. (1987) compared transplanted and seeded tomatoes in their abilities to compete with eastern black nightshade and hairy nightshade over two years. Overall transplanted tomato yields were significantly higher in comparison to seeded tomatoes. These results coincided with previous observations that seeded crops have a lower competitive ability then transplanted crops (Weaver et al. 1987). The use of plastic mulch to suppress weeds has been widely used in horticultural crops, and has contributed to reducing crop loss due to weed infestation (Ngouajio and Ernest 2004). Plastic mulches work in reducing weed infestations by limiting seed germination and reducing seedling development by means of providing a physical barrier that reduces or eliminates light reaching the soil (Ngouajio and Ernest 2004). Fertigation works well in combination with mulches to provide water and nutrients directly to the crops’ root zone. Weaver et al. (1992) found the length of time crops can tolerate weed competition is directly related to the availability of soil moisture and nutrients. They found that while weed emergence is correlated to temperature, weed density is correlated more with soil moisture. By limiting the water and nutrient to the crops’ root zone the crop is given the competitive advantage. Solarization of the soil involves heating the soil usually under transparent plastic film to high temperatures for specific periods, in order to kill pathogens and weeds already within the soil profile. Solarization works in soils with high organic matter, for the organic matter

14 maintains the heat long enough to be effective. Solarization is effective in controlling nightshade germination as nightshade seeds lose viability at

temperatures over 45 oC (Givelberg and Horowitz 1984).

Chemical Control

The use of synthetic herbicides in weed controls success can be seen in

their widespread use in agriculture. Nightshade species are troublesome weeds

in many crops due to their tolerance and resistance to some commonly applied

herbicides including Paraquat (Chase et al. 1998; Ackley et al. 1999; Bedwick et

al. 1990). As well as their long period of germination (April-June), which allow

them to emerge after the herbicides effects have dissipated (Ogg Jr. 1986).

Currently in watermelon crops there are no herbicide labeled to control

nightshade.

Biological Control

Biological control consists of finding a pathogen or a herbivorous insect that

can control the weed. Biological controls usually perform best in isolated

conditions such as in a greenhouse and are less effective in field settings.

Review of Watermelon (Citrullus lanatus)

Watermelon Taxonomical Description

Watermelon (Citrullus lanatus) belongs in the order Cucurbitales, family

Cucurbitaceae. Originally known as Citrullus vulgaris in 1930, L.H. Bailey

proposed dividing cultivated watermelon into two botanical varieties lanatus and

citroides. The genus has been further divided into four species, C. lanatus (syn.

C. vulgaris), C. ecirrhosus, C. colocynthis and C. rehmii (Wehner 2005).

Morphological and cytogenetic tests suggest the four species are cross

15 compatible but due to separate geographical locations, genetic differences, chromosomal structural differences, and flowering differences, the four species

remain separated (Wehner 2005). A herbaceous vining annual, watermelon

lacks a deep taproot but has many long lateral roots exiting from the cortex of the

primary roots. In high moisture conditions, adventitious roots may form

(Robinson and Decker-Walters 1997). The leaves are pinnately divided into three or four pairs of lobes with an occasional non-lobed leaf (Wehner 2005). C.

lanatus has a trailing growth habit with thin, pubescent, angular, grooved stems that can grow up to 9 meters long. At each node, branched tendrils emerge.

Watermelon flowers are small and thought to be less showy than those of other cucurbits. There are staminate (male), pistillate (female), and perfect

(hermaphroditic) flowers often borne in that order upon the plant. Most plants are monoecious with the occasional andromonoecious (male and perfect) types; andromonoecious plants are mostly found in the wild (Wehner 2005). Flowers are borne from the leaf axis (Olson 1995; Peirce 1987; Robinson and Decker-

Walters 1997). The pistillate flowers have an inferior ovary with three stigmatal lobes, while staminate flowers contains three stamens. Both pistillate and staminate corollas are five lobed, yellowish in color and fused together. Once a pistillate flower opens the staminate flower on the node below also opens.

Pistillate flowers last only one day and for uniform fruit development, all three stigmatal lobes must be equally pollinated. One study calculated that 1000 grains of pollen must equally be distributed on the three lobes for uniform melon production; this means that a relatively high honey bee populations are

16 necessary in assuring uniform pollination of the stigma (Olson et al. 2006;

Sanford 1992; Stanghellini et al. 1997). The number of bee visits to a flower is

more important than the length of a bee visit. times (Olson et al. 2005-2006).

Eight visits by a honey bee to each flower was sufficient in assuring uniform fruit

development (Olson et al. 2005-2006). The fruit is round to cylindrical and can

develop up to 60.96 cm long with a rind 1.06-3.81cm thick. The edible fruit is

composed of the endocarp (placental tissue). The seeds are variable in size,

shape, and color and can be light brown to black (Pierce 1987; Robinson and

Decker-Walters 1997). The seeds lack dormancy and can be harvested,

cleaned, dried, and planted the next day. The optimal temperatures range from

29.4-32.2oC and seeds will not germinate below 15.5 oC. Germination can take

two days to two weeks depending on temperature and moisture conditions.

Watermelon Production in Florida

Watermelon requires a long growing season of 60-90 days for maturity

(Olson et al. 2005-2006). High temperatures and high light conditions are necessary for flower and fruit development. The latest published statistics from the 2004 Florida Department of Agriculture and Consumer Services, (FDAC) ranks Florida’s watermelon production as number two in the U.S., holding 18.9% of the market (second only to California). In 2004 watermelon production was a

$67 million industry in Florida, with 10,927 hectares planted (FDAC, 2004). This is up from 2003 when 10,117 hectares were planted at a value of $ 61 million.

The majority of watermelon production in Florida occurs from April through the middle of July. In 2004, the highest value for fruit was in April at $11.51 per

17 hundredweight (cwt) when production is at its lowest; while fruit harvested in May received the second highest price of $9.11 per cwt.

Weed Studies in Watermelon

Research on weed competition in watermelon (Citrullus lanatus) has

focused on the competitive abilities of several different weed species. These studies are ultimately aimed at helping growers direct their weed control efforts

toward the most problematic weeds. Buker et al. (2003) looked at season long

interference of yellow nutsedge (Cyperus esculentus) in watermelon production.

They found that season-long interference from 2 yellow nutsedge plants per m2

resulted in a 10% yield loss in both direct-seeded and transplanted watermelon

(Buker et al. 2003). They determined the minimal weed-free period for direct-

seeded watermelon to be 35 days after planting, and that the biological threshold

for seeded and transplanted watermelon was 37 and 25 yellow nutsedge plants

(Buker et al. 2003). Wallinder and Talbot (1983) examined the effects of

goosegrass (Eleusine indica) competition with watermelon. They found season-

long competition between watermelon and goosegrass at only 3 plants per linear

meter caused a significant reduction in crop yield. Terry et al. (1997) observed

the effects of smooth amaranth (Amaranthus. hybridus) interference in

watermelon. They determined that the critical period of interference between

smooth amaranth and watermelon to be between 0.5 and 3 weeks after

emergence. Season-long interference by smooth amaranth at only 6 plants/m2

caused a 100% yield loss (Terry et al. 1997). Monks and Schultheis (1998)

worked with large crabgrass (Digitaria sanguinalis) and transplanted watermelon

in North Carolina. They determined transplanted that watermelon required a 6-

18 week weed free peroid after transplanting, in order to reach highest marketable

yields. crabgrass after the first 6 weeks had no effect on overall yields (Monks

and Schultheis 1998). These studies reinforce the idea that weed

competitiveness is species specific and that the weed free period lasting up to 6

weeks may be needed for optimal watermelon yields. Using this knowledge

growers can adjust their control measures to match the determined weed free

period to match their weed population.

Watermelon Nutritional and Cultural Requirements

Nutrition

The form of nitrogen (N) can affect the uptake of other essential minerals.

Watermelon cultivars differ in their tolerance to ammonium (NH4); whereas most

varieties grow well with nitrate (NO3) as the primary nitrogen source. In a study

looking at watermelon variety response to nitrogen source, nitrogen uptake was

highest in a 3:1 ratio (NO3:NH4) as compared with a 1:1 or 1:3 ratio (Simonne et

al. 1992). In those plants receiving NO3 as the primary nitrogen source, there

were significantly higher concentrations of other essential nutrients, phosphorus

(P), potassium (K), calcium (Ca) and magnesium (Mg) as compared with plants

receiving 1:1 or 1:3 NO3:NH4 ratios (Simonne et al. 1992). These results suggest

ammonium reduces overall uptake of essential minerals (Simonne et al. 1992).

Calcium (Ca2+) is essential for fruit development and a lack of Ca2+ produces the condition known as blossom end rot. Nitrogen in the form of NO3 is shown to

stimulate calcium uptake whereas NH4 depresses uptake (Taylor and Locascio

2004). Phosphorus (P) is another nutrient that interacts with nitrogen. High

phosphorus rates increase nitrogen absorption, which can result in increased

19 shoot weight (Schultheis and Dufault 1994). Iron (Fe), a mineral needed for

many physiological processes, is also affected by nitrogen source. Iron is highly

sensitive to high pH and since NH4 is known to lower pH, it was hypothesized

that iron would be more readily absorbed with NH4 (Rivero et al. 2003b). But

NO3 increased Fe uptake whereas NH4 caused biotic stress thus reducing

biomass and diminishing Fe concentrations (Rivero et al. 2003b). Manganese

(Mn) toxicity is also influenced by nitrogen source. Manganese toxicity is a

problem in acidic mineral soils with low pH (less than 5). Toxicity can be reduced

by the addition of magnesium because the ions compete for the same ion uptake

sites; but at high Mn concentrations, Mg has no effect. Watermelon can tolerate higher Mn concentrations than some other crops (Elamin and Wilcox 1986a).

Nitrogen in the form of NO3 is best at reducing the toxicity and producing the

highest levels of growth (Elamin and Wilcox 1986b). Nitrogen in NH4 form

reduced growth and suppressed K, Ca, and Mg absorption while increasing N

and P concentrations (Elamin and Wilcox 1986b).

pH has been shown not to affect watermelon seed germination but does

affect root and shoot number (Liu et al. 1994). Although watermelon grows well

in moderately acidic soil, a pH of less than 5 severely reduces productivity

(Sundstrom et al. 1983). Concentrations of Mn2+ at low pH (≥5) have been

shown to be toxic to watermelon, supplemental applications of Ca2+ and Mg2+ will reduce the toxicity (Elamin and Wilcox 1986b; Sundstrom et al. 1983). Low pH

limits Ca2+ availability, which in turn has a negative effect on root growth, fruit set,

sex expression, fruit yield and chemical composition of watermelon (Liu et al.

1994). One study focused on low pH tolerance of individual watermelon cultivars.

Out of all the cultivars tested, Charleston Gray fared the best in low pH (6.5-4), growing normally under the low pH conditions. These results suggest genetic differences between cultivars in the root and shoot growth response to low pH conditions (Liu et al. 1994).

Temperature

Exposure to temperatures higher or lower than optimal can cause both physiological and biochemical damage to plants. Watermelon is more sensitive to low temperatures than high temperatures and grows better at temperatures higher than 32°C (Rivero et al. 2001). Optimum temperature for watermelon growth is around 35°C (Rivero et al. 2001). Temperatures below 15°C can cause major metabolic problems for the plants. Thermal stress in watermelon caused decreased shoot weight, accumulation of soluble phenolics, along with high phenylalanine ammonia-lyase, peroxidase and polyphenol oxidase activity

(Rivero et al. 2001). Cold stress for prolonged periods can reduce growth of transplants and seeded watermelon, although recovery occurs later in the growing season (Korkmaz and Dufault 2001). Cold stress does not affect early yields but does reduce total yields linearly with respect to length of time at low

temperatures. Certain cultivars such as ‘Carnival’ have lower yields after

exposure to cold stress (Korkmaz and Dufault 2001). Iron (Fe) content of

watermelons is most affected at cooler temperatures, with it being limited in

uptake and translocation. At 10°C watermelon begins to show cold stress with

decreased shoot weight, depressed metabolic activities, reduced Fe uptake and higher superoxide dismutase (SOD) activity (Rivero et al. 2003a).

Mulches and Growth: High and Low Maintenance

Watermelons are grown in Florida on elevated beds covered with plastic

mulch or on bare ground. Transplants are used or the plots are directly seeded.

Recommendations for row and plant spacing along with irrigation and fertigation

are provided in the Vegetable Production Handbook for Florida (Olson et al.

2005-2006). Growing watermelon can be done under high intensity, mulched bed, drip fertigation, transplants, or under a low intensity management system; seeded, bare ground, minimal cultivation. Alternatively, watermelon can be grown using a combination of high and low intensity management, an example of which is bare ground with transplants and drip fertigation. Lu et al. (2003) compared high and low intensity management systems with three watermelon cultivars. Two out of three years the high maintenance systems produced 100% greater marketable fruit per hectare and marketable fraction of total fruit yield than the low maintenance system (Lu et al. 2003); although with each cultivar, there were individual differences in performance in response to the level of maintenance.

Mulches

The use of colored mulch has been shown to produce higher watermelon yields in comparison to bare ground and may be useful for protecting against cucumber beetle infestations. Black and white mulches have been shown to increase fruit production whereas silver mulches have been found to lower cucumber beetle populations (Andino and Motsenbocker 2004). Watermelon cultivar Crimson Sweet was grown with different mulches and row covers to analyze the relative growth rate (RGR), net assimilation rate (NAR), specific leaf

22 area (SLA), leaf area index (LAI), and crop growth rate (CGR). With all the mulch types used and row covers, plants showed significant increases in RGR,

NAR, SLA, LAI and CGR. Carbon dioxide levels in the transplant holes of the mulched rows were almost twice that of the ambient carbon dioxide levels

(Soltani et al. 1995). Plants under spun bonded polypropylene polyamide net

(SB-PP) and perforated polyethylene film (PCP) produced the earliest fruits

(Soltani et al. 1995). Early vegetative growth with mulches correlated well with accumulated heat units, and suggested a consistent heat requirement for the cultivar Crimson Sweet to reach the first male flower, first female flower and first harvest for all plants (Soltani et al. 1995).

Plant spacing

Planting density and planting pattern have a large effect on yield response of watermelon (Sanders et al. 1999). The highest yields occurred when transplants were spaced 0.7 to 0.9 m apart within the row, but to produce the

heaviest weights and highest yields the plants need to be spaced 0.9 to 1 m

apart (Sanders et al. 1999). For seeded watermelon, row spacing needed to be

70 cm or greater with spacing of 1.5 m2 producing the highest yields. Goreta et al. (2005) found that increasing plant spacing produced heavier fruit but overall reduced yields per ha. These authors suggested that under good growing conditions 10,000 plants per hectare is reasonable. Under suboptimal conditions, 10,000 plants per ha can be grown if there is a market for smaller fruit (Goreta et al. 2005).

Water and nutrients

Scheduling water and nitrogen inputs can be effective for achieving profitable yields with small risk of NO3 leaching into ground water (Pier and

Doerge 1995a). In a study on nutrient management, Goreta et al. (2005) found

that watermelon yield did not increase with N rates above 115 kg per ha. In this

study they split the nitrogen application and used drip irrigation with plastic

mulching. They concluded that recommendations for watermelon grown on bare

ground could not be used for production with plastic and drip irrigation. In a

study by Kaya et al. (2003), increasing mycorrhizal colonization directly assisted

plants with water uptake and nutrient uptake, especially phosphorus.

Interactions between irrigation and colonization were significant both in shoot and

root growth. Water-stressed plants had a reduction in yields except for where

mycorrhizal colonization occurred. With mycorrhizal colonization, soluble solids

and nutrient concentrations in the plants increased. These results suggest that

under growing conditions that are less than ideal, mycorrhizal fungi can assist

plants in their water use efficiency and over all health.

Transplants versus seeded

Transplants are known to increase early and total yields as compared to

direct seeding when weather conditions are not optimal such as under lower

temperatures (Hall 1989). Hall (1989) found that the dry weight of watermelon

transplants grown in cells 39.3 cm3 were three times greater in weight than

transplants grown in cells 18.8 cm3. The economic advantage of using smaller

cell sizes in transplants is not as important in watermelon production because

watermelon is spaced so that fewer plants are used per hectare. Thus, the

24 economic return of healthier plants and increased fruit production makes up for the additional cost per transplant (Hall 1989).

CHAPTER 2 SEASON-LONG INTERFERENCE BETWEEN WATERMELON AND AMERICAN BLACK NIGHTSHADE

Introduction

Florida is annually one of the top three watermelon producers in the United

States. In 2005 watermelon crops brought in 127 million dollars in profits. A large amount of the Watermelon grown in Florida comes from South Florida, where American Black nightshade (SOLAM) is a problematic weed within watermelon crops. To this date there is no herbicide labeled for use in watermelon crops to control SOLAM. The Environmental Protection Agency denied a request in 2004 for a section 18 label for the herbicide Sinbar to be used in watermelon crops to control SOLAM. They argued that there was no data showing SOLAM was capable of reducing watermelon yields.

Objectives

No previous studies have looked at season long interference of American black nightshade1 (SOLAM) and watermelon variety ‘Mardi Gras’. The objectives of this study were to:

• Determine the competitive effects of season-long SOLAM interference in watermelon • Estimate watermelon yield loss caused by season-long SOLAM interference • Determine the biological threshold of SOLAM interference

1 Letters following this symbol are a WSSA approved computer code from Composite List of Weeds, reviewed.1989. Available only on computer disk from WSSA 810 East 10th Street, Lawrence, KS. 66044-8897.

25 26

Materials and Methods

Additive studies were conducted in the spring of 2005 at the North Florida

Research, Live Oak, Florida (NFREC) and in spring of 2006 at NFREC and the

Plant Science Research and Education Unit, Citra Florida (PSREU). These studies were conducted to determine the effects of season-long American black nightshade (Solanum americanum: SOLAM) interference with ‘Mardi Gras’ watermelon (Citrullus lanatus). The soil at the NFREC is a Lakeland series sand

(Thermic, coated, Typic Quartzipsamments): 95% sand, 4% silt, 1% clay, 1% organic matter, and a cation exchange capacity of 4.9. The soil pH at the

NFREC was 6.7 in 2005 and 2006. The soil at PSREU is a Hague series sand

(Typic Paleudalfs): 84.4% sand, 5.2% silt, 10.4% clay, 1.4% organic matter and a cation exchange capacity of 6.1 with a pH of 5.8. Prior to mulching, soil was limed to a pH of 6.5. Bed widths were 1 m (39 in) wide and 2.4 m (8 ft) from row middle to row middle. Two weeks prior to planting, soil was fumigated with a mixture of methyl bromide:chloropicrin in a 98:2 ratio, at the rate 392 kg/ha. At the time of fumigation, black polyethylene mulch along with drip tape to accommodate fertigation, were applied over the raised seedbeds. One week after fumigation, the mulch was removed on rows designated to represent the non-mulch trials. Plasticulture production and drip fertigation practices followed the recommendations of the University of Florida IFAS Extension Service (Olson and Simonne 2005-2006). Weeds other than nightshade that emerged were removed by hand or by mechanical means. Prior to transplanting, openings were punched along the center of the plastic mulch at one meter intervals. ‘Mardi

Gras’ watermelon transplants were grown at Speedling Inc. Sun City Florida from

27 seed we provided. Watermelon transplants were planted on March 31st and April

1st, 2005 at the NFREC, and on March 23rd and 27th, 2006, at the PSREU and

NFREC respectively. There were four watermelon plants per plot and each plot

was 6 m (19.5 ft) long. Watermelon spacing was 1-meter in row. Pest

management was implemented according to the University of Florida IFAS

Extension Service recommendations (Olson and Simonne; 2005-2006).

Approximately 6-8 weeks prior to planting, American black nightshade was

seeded into 1 in cells in Speedling Inc. trays and grown in a greenhouse. At the

time of planting, nightshade seedlings (5 cm high) were transplanted 10 cm (4 in)

from the watermelon transplants and each other. At the time of planting

nightshade transplants ranged from 5 to 7 weeks in age. Treatments consisted

of American black nightshade transplants planted at four plants per unit area (2,

4, 6, and 8), with the control being a weed-free plot. Nightshade treatments were transplanted in concurrence with the watermelon plantings at all locations on the same day.

Measurable Variables

Measurable variables included fruit yield, weed biomass, photosynthetically active radiation (PAR) and plant measurements. In 2005, all fruits were harvested, weighed and counted; while in 2006 all fruit were graded for marketability. To measure weed biomass, one nightshade plant from each plot was cut at the soil line and dried at 43°C (110°F) in a drying room for 5 to 6 days.

At PSREU nightshade was cut the day of harvesting melons while at NFREC nightshade was cut 6 days after harvesting melons. Nightshade plants included

any berries that were present. Shoot dry weights were recorded and analyzed

28 for each treatment. Light intensity was measured at the NFREC in the 2005 trial using a Li-Cor 1-m line quantum sensor placed parallel to the length of the row along side the watermelon vines in two locations in each plot during the full bloom stage of the watermelon plants. Ambient PAR was recorded above watermelon vines in the control plots. Measurements were taken on clear days between 11:00 am and 1:00 pm. The two photon flux density values (in µmol m-2

s-1) from each plot were averaged and graphed for each treatment. PAR

measurements were expressed as percent of control Plant measurements

included canopy width and height of nightshade and vine length of watermelon.

Both nightshade height and watermelon vine length measurements were from

the base of the plant to the upper most nodes of the plants. Measurements (in

cm) were taken weekly on both watermelon and nightshade plants starting in

May for each treatment. Two randomly chosen plants of both watermelon and

nightshade were measured from each treatment and these measurements were

averaged. Measurements of vine length were ended after week eight to avoid

causing damage to the fruits and vines.

Experimental Design and Statistical Analysis

In all trials, a randomized complete block design was used with five

treatments and four replicates. Data were converted into percent of control in

order to normalize trends between trials and locations. The converted data was

then analyzed using proc glm to generate an ANOVA to test for significant main

effects and interactions at the 5% level (SAS, 2006). Year and location were

analyzed to reveal any possible significant interactions on the dependent

variables. All converted data were then regressed using SAS to show

29 differences in treatments by mulch type. Proc regress showed the data was not

linear so proc nlin was used to find the best fitting curve for the data.

Results

Analysis of data from the 2005 and 2006 trials revealed yields were significantly affected by nightshade density and mulch type. Due to significant

interaction by year, data were analyzed separately for each year. In 2006 there

was no significant location interaction so data were combined. In both years and

at both locations the maximum yield loss occurred at 2 nightshade plants per m2.

The relationships between the watermelon yields number of melons and nightshade density for the mulched and non-mulched trials was best represented by rectangular hyperbola models similar to the one described by Cousens (1985)

Y= a0 X x/(1+ a0 X X /a1). In this equation Y is the yield loss as a percentage of

the control, a0 is the yield loss at low densities of nightshade, a1 represents the

rate of yield loss as nightshade density increases and x represents any

nightshade density.

2005

One trial was conducted at the NFREC in 2005. A second trial at the

PSREU had been planed but due to high disease pressure and a lack of

nightshade transplants only one trial was conducted. Total fruit weight and

number were recorded and analyzed. Data analysis showed that there was an

interaction between mulch versus non-mulch trials. In mulch trials watermelon

yields were statistically higher for each nightshade treatment than in the non-

mulched trials. A rectangular hyperbola model was used to characterize the

relationships between total fruit yield and total fruit number and nightshade

30 treatment densities (Figure 2-1 and 2-2). While in the case of the non-mulch treatment, there were no yields in any of the nightshade treatments thus showing that nightshade was the better competitor (data not shown). We believe the reason the non-mulch trial had no yields was due to the above average amount of rain that occurred in 2005 (appendix A). The saturated soil most likely weakened plants that were already stressed due to nightshade competition. In both trials, maximum yield loss or biological threshold occurred at two nightshade plants/m2, which caused yield losses of 100% (data not shown) and 80% in the

non-mulched and mulched treatments, respectively. The average yield per plot

for the non-mulched control was 21 kg (47 Lbs). The average yield per plot for the mulched control was 80 kg (176 Lbs).

2006

In 2006, trials were conducted at the NFREC and the PSREU locations simultaneously. There were interactions between mulched versus non-mulched trials and nightshade treatments. There were no interactions by location for the mulched and non-mulched trials; therefore, the like trials were combined. At the

PSREU, two harvests were done to look at early season versus late season yields but at NFREC, Only one harvest was made. Due to the differences in the

number of harvests at the two locations, data was combined for total yields and

total marketable yields. In both non-mulched and mulched trials, the data

analysis revealed that total marketable yield and number of fruit were significantly

affected by nightshade density (P ≤ 0.05). The relationships for total marketable

yield and number of fruit in both non-mulched and mulched trials were best

represented by rectangular hyperbola models (Figures 2-3 and 2-5, 2-4 2-6). In

31 both mulched and non-mulched trials, the biological threshold occurred at two nightshade plants/m2 which caused yield losses of 70% and 54% in non-mulched

and mulched treatments respectively. The average yield for the non-mulched

controls were 49 kg (89 Lbs), while the average yield for the mulched controls

were 68 kg (150 Lbs). Total yields and total number of melons were both significantly affected by nightshade density. The relationships for total yields and total number of melons were best represented by rectangular hyperbola model

(Figures 2-7, 2-8, 2-9 and 2-10). There was an interaction by site for the average melon weight for each treatment, but there was no significant differences in average melon weight for each mulch trial.

Nightshade Dry Weight

Analysis of dry weight data per plant showed that nightshade dry weight

was significantly affected by nightshade density. Nightshade dry weight did not

differ significantly by mulch type, or locations; therefore, all data were combined.

Figure 2-11 shows the relationship between nightshade weight and density. At the density of 8 plant per m2 nightshade dry weight was lower (37%) than the dry

weight of 2 plants/m2.

PAR.

Nightshade density had a significant effect on photosynthetically active

radiation (PAR) levels. Figures 2-13 and 2-14 display the level of

photosynthetically active radiation reaching the watermelon vines on non-mulch and mulch as affected by season-long interference at different densities of nightshade. and their relationships were best represented by a rectangular hyperbola model with an R2 value of 0.93 and 0.95 on non-mulch and mulch,

32 respectively. The maximum PAR reduction was 73% and 79% less than the

control at 2 nightshade per m2 on non-mulched and mulched respectively.

Plant Measurements.

Watermelon vine length. There was no interaction in overall watermelon

vine length between treatment and locations, while there were interactions by

mulch trial, therefore the data were combined for both locations by mulch type.

By week eight, there were no significant differences in vine length within mulch trial. The vine lengths by week eight were 2.07 m (6.79 ft) and 2.56 m (8.4 ft) for

non-mulch and mulched treatments respectively (data not shown). Figures 2-15

& 2-16, show the effects of SOLAM density on length of watermelon vines at 6, 7

and 8 weeks after planting (WAP).

Nightshade. There were interactions in nightshade height between densities by locations, although there were no interactions by locations in the canopy widths of the different nightshade treatments (P ≤ 0.05). By week eight,

the heights of nightshade plants were 1.13 m (3.7 ft) and 0.94 cm (3.1 ft) at the

NFREC and PSREU respectively. By week eight, the canopy width for

nightshade plants at both locations was 1.57 m (5.15 ft) (data not shown).

Figures 2-15, 2-16, 2-17, 2-18 2-19 and 2-20; display the growth of the different

nightshade treatments by locations and mulch type.

Discussion

Watermelon plants with nightshade interference produced fewer and

smaller fruit than when grown weed-free. Over both years and at both locations,

the biological threshold occurred at two nightshade per m2. In 2005, 2

nightshade plants/m2 reduced yields by 100% in non-mulched and 80% in

33 mulched treatments. The lack of yields for the non-mulched trial is thought to be related to the high amount of rain fall in 2005 (appendix a). In 2006, yields were higher in both total and marketable fruits, yet only 2 nightshade per m2 reduced

yields by 70% and 54% in non-mulched and mulched trials respectively. Dry

weights of nightshade plants suggests that as density of nightshade increased

the individual weight of the nightshade plants decreased. At higher densities,

intraspecific competition among plants could limit individual plant growth. Roos

(1999) looked at intraspecific competition in nightshade and found plant dry

weight significantly decreased as density and proportion increased. In the

current study PAR levels measured during the full bloom stage of watermelon

growth showed significant shading by nightshade on the prostrate watermelon

vines. The lower amount available to the watermelon most likely reduced over all

plant vigor. As nightshade density increased, the amount of PAR reaching the

vines decreased. PAR was reduced by 73% and 79% in non-mulched and

mulched trials respectively, at only 2 nightshade per m2. The heights of the

nightshade plants did not differ in response to density although they did differ by

location. Canopy widths of nightshade plants did not significantly differ in

response to density or by location. This agrees with what Roos (1999) found

when she studied intraspecific competition between nightshade plants. She

found that plant density and proportion did not affect plant height. In our case,

the height differences could be more associated with the differences in climatic

conditions at each locations, PSREU is further south and had higher average

temperatures than NFREC, suggesting in cooler average temperatures

34 nightshade plants tend to grow taller putting more energy into height and less into girth. Length of the watermelon vines did significantly differ by mulch trial but not by nightshade density. This is to be expected as watermelon plants growing on mulch produces more fruit and in turn longer vines due to greater overall vigor

(Lu et al. 2003). We did notice that the stem diameter of watermelon vines were smaller as the nightshade density increased (data not shown). This reduction in vine width could be a sign of a reduction in overall vigor by those plants being shaded by the nightshade treatments. Future studies on watermelon and weed interference should investigate the effects weeds have on vine width. The low fruit set by watermelon plants could have been caused by nightshade height and canopy size which created a physical barrier to visiting bees in locating watermelon flowers beneath. Nightshade height also affected competition by limiting the amount of available light reaching the prostrate watermelon vines.

This is similar to the results of Ponce et al. (1996) in their study of black

nightshade (S. nigrum) height as a factor of competition with tomato and pepper

plants in greenhouse trials. They found height gave nightshade a strong

competitive advantage in obtaining light and nutrients. Nutrient accumulation is

another factor that might have assisted nightshade competition. Qasem (1992)

studied nutrient accumulation by tomato and bean in comparison to nightshade

and determined that nightshade to be a better nutrient accumulator than either crop. In many studies nightshade has been found to be highly responsive in its

growth, to the amount of available nutrients within the soil (Blackshaw et al.,

2004; Khan et al., 1995; Khan et al., 2000; Wahle and Masiunas, 2003). The

35 abilities of nightshade to accumulate nutrients would have given the weed an

advantage especially during critical times of watermelon growth such as during

flowering and fruit development. Overall plant height, and the responsiveness of

nightshade to available nutrients helped make nightshade a strong competitor within the watermelon crop.

Figure 2-1. Yields of watermelon fruit 2005 as affected by season-long interference at different SOLAM densities on mulch. The model is Y=a0 * x/(1 + a0 * x/a1), where a0 = 235 and a1=100.

Figure 2-2. Number of watermelon fruit as affected by season-long interference at different SOLAM densities. The model is Y = a0 *x/(1 + a0 * x/a1), where a0 = 146 and a1 =100.

Figure 2-3. Yields of marketable watermelon fruit 2006 as affected by season-long interference at different SOLAM densities (non-mulched). The model is Y = a0 *x/(1 + a0 * x/a1), where a0 = 115 and a1 =100.

Figure 2-4. Yields of marketable watermelon fruit 2006 as affected by season-long interference at different SOLAM densities (mulched). The model is Y = a0 *x/(1 + a0 * x/a1), where a0 = 60.2917 and a1 =100.

Figure 2-5. Total number of marketable watermelon fruit as affected by season-long interference at different SOLAM densities (non-mulched). The model is Y = a0 *x/(1 + a0 * x/a1), where a0 = 83.0159 and a1 = 100.

Figure 2-6. Total number of marketable watermelon fruit as affected by season-long interference at different SOLAM densities (mulched). The model is Y = a0 *x/(1 + a0 * x/a1), where a0 = 47.8918 and a1 = 100.

Figure 2-7. Total yields of watermelon fruit as affected by season-long interference at different SOLAM densities (non-mulched). Model is Y = a0 *x/(1 + a0 * x/a1), where a0 = 73.2858 and a1 =93.6802.

Figure 2-8. Total yields of watermelon fruit as affected by season-long interference at different SOLAM densities (mulched). The Model is Y = a0 *x/(1 + a0 * x/a1), where a0 = 35.7464 and a1 =100

Figure 2-9. Total number of watermelon fruit as affected by season-long interference at different SOLAM densities (non-mulched). The model is Y = a0 *x/(1 + a0 * x/a1), where a0 = 53.9670 and a1 = 75.6295.

Figure 2-10. Total number of watermelon fruit as affected by season-long interference at different SOLAM densities (mulched). The model is Y = a0 *x/(1 + a0 * x/a1), where a0 = 20.2910 and a1 = 100.

Figure 2-11. SOLAM dry weight after season-long interference at different SOLAM densities in 2006.

Season-Long Competition: Photosynthetically Active Radiation (Non-mulch)

120 100 80 60 40 20 PAR (% of Control) of (% PAR 0 02468 SOLAM Density/m2

Figure 2-12. The level of photosynthetically active radiation (PAR) reaching watermelon vines at the full bloom stage, as affected by season-long interference at different SOLAM densities.

Season-Long Competiton: Photosynthetically Active Radiation (Mulched)

120 100 80 60 40

PAR (%of PAR Control) 20 0 02468 SOLAM Density/m 2

Figure 2-13. The level of photosynthetically active radiation (PAR) reaching watermelon vines at the full bloom stage, as affected by season-long interference at different SOLAM densities.

Length of Watermelon Runner/Treatment Mulch

350 300 250 Week 6 200 Week 7 150 100 Week 8 50 Lenght of Runner (cm) ofLenght Runner 0 02468 SOLAM Density/m2

Figure 2-14. The length of watermelon vines by SOLAM treatment (mulch): 6, 7 and 8 weeks after planting.

Lenght of Watermelon Runner/Treatment Non-Mulch

350 300 250 Week 6 200 Week 7 150 100 Week 8 50 Length of Runner (cm) ofLength Runner 0 02468 SOLAM Density/m2

Figure 2-15. The length of watermelon vines by SOLAM treatment (non-mulch): 6, 7 and 8 weeks after planting.

Height of SOLAM/Treatment Mulch (NFREC)

140 120 100 6 WAP 80 7 WAP 60 8 WAP 40 9 WAP 20 Height of SOLAM (cm) of SOLAM Height 0 2468 SOLAM Density/m2

Figure 2-16. The height of nightshade plants by treatment (mulch) at the NFREC: 6, 7, 8, and 9 weeks after planting.

Height of SOLAM/Treatment Non-Mulch (NFREC)

120 100 6 WAP 80 7 WAP 60 8 WAP 40 9 WAP 20 Height (cm) SOLAM 0 2468 SOLAM Density/m2

Figure 2-17. The height of nightshade plants by treatment (non-mulch) at the NFREC: 6, 7, 8, and 9 Weeks after Planting.

Height of SOLAM/Treatment Mulch (PSREC)

120 100 80 6 WAP 60 8 WAP 40 9 WAP 20 Height (cm) SOLAM 0 2468 SOLAM Density/m2

Figure 2-18. The height of nightshade plants by treatment (mulch) at the PSREU: 6, 7, and 9 weeks after planting.

Height of SOLAM/Treatment Non-Mulch (PSREC)

120 100 80 6 WAP 60 8 WAP 40 9 WAP 20 Height of SOLAM (cm) of SOLAM Height 0 2468 SOLAM Density/m2

Figure 2-19. The height of nightshade plants by treatment (non-mulch) at the PSREU:6, 8, and 9 weeks after planting.

CHAPTER 3 SPATIAL DISTANCE STUDY BETWEEN AMERICAN BLACK NIGHTSHADE (Solanum americanum Mill.) AND WATERMELON (Citrullus lanatus L.)

Objective

No studies have been done to examine the spatial distance between

American black nightshade and watermelon on their abilities to compete with each other. The objectives of this study were to determine if spatial distances of

15 and 30 cm have an effect on the ability of nightshade to compete with watermelon plants as compared a weed-free control.

Materials and Methods

Studies were conducted in spring of 2006 at the North Florida Research and Education Center, Live Oak, Florida (NFREC); and at the Plant Science

Research and Education Center, Citra Florida (PSREU). The soil type at the

NFREC is a Lakeland series sand (Thermic, coated, Typic Quartzipsamments):

95% sand, 4% silt, 1% clay, 1% organic matter, and a cation exchange capacity of 4.9. The soil pH at the NFREC was 6.7 in 2006. The soil at PSREU is a

Hague series sand (Typic Paleudalfs): 84.4% sand, 5.2% silt, 10.4% clay, 1.4% organic matter and a cation exchange capacity of 6.1 with a pH of 5.8. Soil was limed to a pH of 6.5, prior to mulching. Bed widths were 1 m (39 in) wide and 2.4 m (7.8 ft) from center to center. Two weeks prior to planting, methyl bromide was injected at a rate of 392 kg/ha in a 98:2 ratio of methyl bromide: chloropicrin, in concurrence with the application of black polyethylene mulch. Drip tape was

46 47 placed under the mulch to provide fertigation for the plants. Plasticulture production practices and drip fertigation followed the recommendations of the

University of Florida IFAS Extension Service (Olson and Simonne 2005-2006).

Weeds other than nightshade were removed by mechanical means or by hand.

Openings were punched along the center of the plastic mulch, 1 m (39 in) apart, prior to transplanting. American black nightshade was seeded into Speedling

Inc. trays and grown in a greenhouse for 6-8 weeks prior to being transplanted into the field. At the time of planting nightshade transplants ranged from 5 to 7 weeks in age. On March 31st, watermelon variety ‘Mardi Gras’ were transplanted into the beds. Watermelon transplants were grown at Speedling

Inc. Sun City, Florida from seed we provided. There were four watermelon plants per plot and each plot was 5 m (16.4 ft) in length. Nightshade was transplanted on the same day as the watermelon plantings at both locations. Nightshade treatments consisted of two nightshade seedlings planted at either 15 cm or 30 cm on either side of the watermelon plant. At the time of transplanting nightshade was 5-10 cm in height. At both locations the third treatment was a weed-free control.

Measurable Variables

Measurable variables included fruit yield, weed dry weight, and plant measurements. Manual harvesting of watermelons was conducted on June 2nd and 9th at the PSREU and on June 8th at the NFREC. At both locations all watermelon fruits were harvested, weighed, counted, and graded for marketability. The number of fruit and their weights were recorded for each plot.

To get weed dry weight, one nightshade plant was hand-cut from each plot

48 bagged and dried in a forced air drying room at 43°C (110°F) for 4 or more days.

The weights of the dried plants were recorded for each treatment.

Measurements were taken on a weekly basis starting in May to determine the effect of late season competition on watermelon vine length and nightshade height and canopy width.

Experimental Design and Statistical Analysis

At both locations, a randomized block design was used with three treatments and four replications. The data were analyzed using ANOVA to test for significant treatment effects and interactions at the 5% level (SAS, 2006).

Data were converted into percent of control in order to normalize trends between the locations. Locations were analyzed to reveal any possible significant interaction on the dependent variables.

Results and Discussion

Analysis of both marketable yields and total yields revealed no interaction between treatment and location, therefore, for both marketable and total yield data for the locations were combined. Initially we intended to harvest the melons more than once at each location to compare early and late season yields, but at the NFREC all melons were harvested before we could instruct the crew to do otherwise. Both the 15 cm and 30 cm spacing’s significantly reduced watermelon yields. (Table 3-1).

Plant Measurements. There were no interactions by site or by treatment for the plant measurements. While the each treatment differed in the average length of the watermelon vines and the height and width of the nightshade canopy, measurement differences were statistically significant at p = ≤ 0.05.

The average watermelon vine length was 2 m (6.5 ft). While the average canopy

was 84 cm (2.8 ft) high and 1.4 m (4.6 ft) wide (data not shown). There were no interaction by location or by treatment for nightshade dry weight at p = ≤ 0.05 .

The average dry weight for both treatments was 954 g. (data not shown).

Nightshade Dry Weights. The nightshade dry weights for both treatments were not significantly different therefore they were combined. Nightshade and watermelon measurements were not significantly different, therefore suggesting that late season competition does not affect plant height, width or vine length suggesting, that spacing of nightshade at the low density of two plants/m2 has no effect on overall plant size.

Overall, there were no significant differences watermelon and nightshade plant measurements or nightshade dry weight. These results agree with lack of statistical differences in the two nightshade spacing’s (15 and 30 cm) examined in this study. Current watermelon spacing recommendations from IFAS

(Simonne and Olson, 2006) suggest plantings watermelon from 60 cm to 1 m 83 cm. This suggests that if growers following IFAS recommendations have any nightshade plants growing in their watermelon beds, these plants will be close enough in proximity to the watermelon plants to significantly reduce those plants yields. Therefore it’s in the best interest of the grower to remove nightshade found growing in the field as early as possible to maintain their yields.

Table 3-1. Treatment effects on watermelon yields as percent of control. Treatments are spacing from watermelon plants. Treatment % of Control

Control 100a

30 cm 74bc

15 cm 46c a Means within rows followed by same letter do not differ at P=0.05 as determined by LSD

CHAPTER 4 SEED GERMINATION TRIALS USING AMERICAN BLACK NIGHTSHADE SEED

Objectives

American black nightshade seeds do not germinate readily in an experimental setting due to dormancy mechanisms that allow for the seed to lay dormant in the seed bank for many years. The efficacy of six seed treatments were evaluated for breaking dormancy in American black nightshade.

Material and Methods

Seed germinations studies were conducted in 2005 and 2006 using

American black nightshade seed (Solanum americanum). Ripened berries from several plants were collected from the greenhouse or from the field from plants grown from the same seed source in July of 2005. Seeds were extracted from the berries directly, by crushing the berries in a container of water and separating the pulp from the seeds; or by fermenting crushed berries for a period of three to four days, then washing them in water. The extracted seeds were then laid out to air dry at room temperature. The dried seeds were divided with portions of both non-fermented and fermented seed undergoing further treatments.

Throughout the study, directly extracted seed served the control for non- fermented treatments, while seed extracted from fermented berries served as a control for fermented treatments. Additional treatments were treating the seeds

51 52 with sodium hypochlorite (NaClO) or pre-treating by soaking the seed with

aeration provide by an aquarium bubbler (bubbling).

Bleach treatment

Seeds were placed in a solution of 2.7% sodium hypochlorite (half strength

household bleach) and water at a 1 to 2 ratio for 30 minutes. After soaking, the

seeds were rinsed repeatedly and left to dry. Once dried, seeds were placed in a

container and stored in a refrigerator at 40° F (4°C) until used in experiments.

The bleaching treatment followed the protocol for improving germination of

solanaceous species, (Rick and Borgnino 1996-2006). The bleach treatments

were done prior to germination trials on September 2nd 2005, November 3rd 2005

and January 23rd 2006.

Pre-germination treatment

The pre-germination treatment (bubbling) involved soaking seed in water with continuous aeration being provided by an air stone aquarium aerator. The

water was renewed continually throughout the experiment from a faucet dripping

from above. To keep the seeds from floating out of the container, they were held

in a nylon stocking. Once set up, the treatment was left running for a period of

three or four days, after which the seeds were removed, dried and used in

experiments. The pre-germination treatments were conducted on September 2nd

through the 5th 2005 for trial one, on November 3rd though the 7th 2005 for trial

two and on January 23rd through the 26th 2006 for trial three.

Germination trials

Trials consisted of the six seed treatments (except for the first trial which

consisted of five treatments). Treatments included non-fermented control, non-

53 fermented bubbled, non-fermented Clorox, fermented control, fermented bubbled and fermented Clorox. Seeds were germinated in petri dishes on filter paper that was saturated in water and sealed with parafilm. Water was added to keep the filter paper moist as necessary throughout the experiment. Each plate contained

40 seeds. There were four replicates of each treatment. The plates were numbered 1-24 (except trial 1) and the numbers were randomly assigned to each treatment using a random number table. The plates were left under indirect light in a randomized manner on a window sill at ambient room temperature (26°C).

During the trials, plates were opened every two days and any germinating seed was counted and removed from the plate. Each trial lasted 14 days with germination counts taken every two days. Seeds were considered germinating when the radical had emerged.

Statistical Analysis

The experiment had a completely randomized design with four replicates for each treatment. Cumulative number of germinated seeds in each plate were expressed as a percent of total number of incubated seeds. All data were subjected to ANOVA and mean separation was carried out using LSD at the 0.05 level (SAS 2006). Because of significant interactions between trials and treatments; each trial was analyzed separately.

Results

There were significant differences between treatments, day*treatments, trial*treatments, and trial*day*treatment. By day 10 all the treatments had reached the peak of germination with fewer numbers of seed germinating after day 10 than before.

Trial 1: September 8-22, 2005

Trial one had the fewest overall percentages of germinating seed; which is believed to be due to known seed dormancy effects that occur soon after harvesting and which dissipate over time (Givelberg and Horwitz 1984). This trial

consisted of five treatments, and was missing the non-fermented Clorox

treatment that was added to later trials. After 14 days of incubation The

fermented Clorox treatment resulted in the highest percent of germinated seed,

93% (Table 1). Both the non-fermented and fermented bubbled treatments

produced the second highest percentages germinated seed (69% and 67%,

respectively). While fermenting the seed did improve germination over the non-

fermented seed, it only managed to produce an average of 45% germination as

compared to the 21% germination by the non-fermented control.

Trial 2: November 3-17, 2005

The non-fermented Clorox treatment was added to this trial and the

following trial (table 2). By 14 days after incubation there was no statistical

difference in non-fermented seeds treated with Clorox, non-fermented bubbled

seeds and the fermented bubbled seeds (Table 2). The non-fermented Clorox

treated seeds had 99% germination; while was non-fermented bubbled seeds

had 98% germination and the fermented bubbled seeds had 91% germination.

The Clorox treated fermented seed produced a significantly lower percentage of

germinating seed than its non-fermented counterpart (89%). Both the non-

fermented and fermented controls were equal in their percentage of overall

germination equaling 84%.

Trial 3: January 29- Febuary 12, 2006

By day 14 there was no statistical differences in the fermented seeds treated with Clorox, the non-fermented Clorox, and the non-fermented bubbled treated seeds (Table 3). By day 14 fermented seeds treated with Clorox had

98% seed germinated, the non-fermented Clorox 95% seeds germinated, the fermented control 93% of the seeds germinated and the non-fermented bubbled treated seeds had 88% seeds germinated.

Discussion

In each trial the Clorox treatments produced the highest overall percentages of germinating seeds while the bubbling treatments came in a close second; for both non-fermented and fermented seeds;. These results suggest that both treatments are effective at removing seed dormancy mechanisms.

Fermentation of seed did increase germination in both trials 1 and 3 while in trial

2 the controls were equal in their overall percentages of germination. This

differed from previous results by Wagenvoort and Van opstal (1979), where they

found soaking/bubbling seed in tap water for 12 hours that was renewed three

times, did not significantly increase germination. In our study we soaked/bubbled

the seed for approximately 72 hours during the bubbling process, and unlike

Wagenvoort and Van opstal results, soaking/bubbling did increase germination.

Overall percentages of germination from all treatments in trial 1 were the lowest of the three trials. While in trials 2 and 3 the treatments resulted in over 50 percent germination and many in high percentages of germination. This is similar to what Givelberg and Horwitz (1984) found which shows that soon after harvest dormancy mechanisms are the strongest but then they dissipate over

56 time. In seeds that are to be germinated soon after harvest, a Clorox treatment may result in the highest germination.

Table 4-1. Germination percentages of American black nightshade seed by days: September 8-22nd 2005. Non-Fermented Fermented Treatment Control Bubbled Control Bubbled Clorox Days % germination 2 0c 46a 0c 28b 0c 4 3c 66a 1c 49ab 35b 6 12b 67ab 23b 63a 75a 8 c ab c b a 19 68 39 64 87 10 20d 69b 44c 66bc 90a 12 d b c bc a 14 21 69 45 67 93 a Means within rows followed by same letter do not differ at P=0.05 as determined by LSD

Table 4-2. Germination percentages of American black nightshade seed by days: November 3rd-17th 2005. Non-Fermented Fermented Treatment Control Bubbled Clorox Control Bubbled Clorox Days % germination 2 0a 0a 0a 0a 0a 0a 4 1d 96a 73ab 0d 68b 31c 6 34b 97a 96a 2c 74a 68a 8 56b 98a 99a 21c 82a 86a 10 72bc 98a 99a 47c 86ab 88ab 12 83bc 98a 99a 78c 88b 88bc 14 84b 98a 99a 84b 91ab 89b a Means within rows followed by same letter do not differ at P=0.05 as determined by LSD

Table 4-3. Germination percentages of American black nightshade seed by days: January 29th-Febuary 12th 2006. Non-Fermented Fermented Treatment Control Bubble Clorox Control Bubble Clorox Days % germination 2 0a 0a 0a 0a 0a 0a 4 0b 0b 4ab 0b 0b 9a 6 16cd 41bc 46b 11d 15d 93a 8 36c 63b 71b 42c 41c 95a 10 51c 78ab 89a 78ab 63bc 96a 12 54c 83ab 92a 90a 73b 98a 14 64c 88ab 95ab 93ab 84b 98a a Means within rows followed by same letter do not differ at P=0.05 as determined by LSD

Table 4-4. Germination percentages of American black nightshade seed for each trial by day 14. Non-Fermented Fermented Treatment Control Bubble Clorox Control Bubble Clorox Trials % germination 1 21 69 * 45 67 93 2 84 98 99 84 91 89 3 64 88 95 93 84 98 *in trial one there was no non-fermented Clorox treatments

CHAPTER 5 SUMMARY AND CONCLUSIONS

The objectives for this research were to determine the effects of season-

long nightshade interference in watermelon, to estimate watermelon yield loss caused by season-long nightshade interference and to determine the biological threshold of nightshade interference. Season-long competition studies demonstrated watermelon has a very low tolerance for American black nightshade interference. Nightshade interference had a negative impact on watermelon fruit yields, weight and the number of fruit. The biological threshold for nightshade interference in watermelon was reached at the density of 2 nightshade plants per meter square for both the mulched and non-mulched trials.

At only 2 nightshade plants per meter square there was an overall reduction in watermelon yields and the number of fruits by 80 to 100% in 2005 and 54 to 70%

in 2006 (mulched and non-mulched trials respectively). Average fruit weight at 2

nightshade per meter square was reduced by approximately 2 kg in 2005 and

2006.

Currently there is no herbicide registered for use on nightshade growing in watermelon crops. Nightshade interferes with crop production by reducing the amount of light, and nutrients available to the watermelon plants. Growing watermelon on mulched beds with drip irrigation improves the competitive abilities of the crop. Plants grown on mulch produced larger yields and more marketable fruit than their counterparts on non-mulch. Mulch increases soil

59 60

temperatures and retains moisture which assists the crop in overall growth and

vigor. In the mulched trials watermelon vines were longer and produced more

fruit than watermelon grown without mulch. These results agree with previous

studies which found mulch assisted plants in their overall vigor and production

(Lu et al., 2003; Andino and Motsenbocker 2004; Soltani et al. 1995). Spatial

distances of 15 and 30 cm between watermelon and nightshade plants resulted

in the same amount of nightshade interference. Nightshade plants growing

within watermelon fields (with recommended bed and plant spacing for

watermelon production) would cause significant reductions in watermelon yields

if nightshade are allowed to compete throughout the season.

The objective for the germination trials was to test six seed treatments to

determine which seed treatment was best at reducing nightshade seed

dormancy. There were statistical interactions for each trial, therefore each trial

was analysis separately. The first trial having the lowest percentages of

germination for all treatments, with the one exception of the fermented Clorox treatment which had 93% germination by day14. The low overall germination of all treatments within trial 1 could be the result of known dormancy mechanisms

soon after fruit harvest, which dissipate over time. In all three trials, the bleach

treatment was most effective in improving germination and producing the highest

percentages of germinating seed. The pre-germination treatment (bubbling) was

another treatment that proved effective in trials two and three in improving

germination of nightshade seed as compared to the controls.

American black nightshade interference in watermelon crops is a problem in

South Florida. Currently there are no herbicides labeled to treat nightshade interference in watermelon. Hence this research was designed to demonstrate the degree of damage in the form of watermelon yield reductions that can result if nightshade if left untreated for an entire growing season. The recommendations of this study are to remove of all nightshade found growing in watermelon beds to prevent any reductions in yields.

APPENDIX ENVIRONMENTAL CONDITIONS FOR EACH YEAR AND SITE

Table A-1. Environmental conditions for the North Florida Research and Education Center (NFREC) 2005. Month April May June* Average Average Air 28.52 33.5 34.06 32.03 Temperature (C) Average Soil 25.52 31.68 33.94 30.37 Temperature (C) Precipitation 5.54 2.54 2.52 3.53 (in)

Table A-2. Environmental conditions for the North Florida Research and Education Center (NFREC) 2006. Month March* April May June* Average Average Air 13.85 20.58 22.91 24.29 20.4 Temperature (C) Average Soil 18.79 24.2 27.52 28.9 24.85 Temperature (C) Precipitation 0.25 1.97 1.75 1.6 1.39 (in)

Table A-3. Environmental conditions for the Plant Science Research and Education Unit (PSREU) 2006. Month March* April May June* Average Average Air 15.08 21.8 24.04 24.89 21.45 Temperature (C) Average Soil 21.15 25.85 29.04 28.7 26.1 Temperature (C) Precipitation 0 2.03 0.46 0.72 0.8 (in) Months with * only include meteorological data for the days the crop was in the field.

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BIOGRAPHICAL SKETCH

Born in Ithaca, New York, Celeste was introduced to botany at an early age when her grandmother took her on long walks into the nearby woods and meadows to collect wild flowers. At home, her mother’s green thumb always

provided fresh vegetables throughout the short northern summers. Her early

experiences with her grandmother and mother left lasting impressions that were

recognized at a later age. At the age of 15, Celeste moved to Sarasota, Florida,

with her family where she finished high school and developed many of the

friendships she still holds dear to this day. In 1997, she moved back to New

York, where she worked for a nonprofit company providing daily living assistance

to clients suffering from different mental illnesses. It was this job that served as

the impetus she needed to return to school and pursue an education related to

her passion for plants. In 2003, Celeste received her bachelor’s degree from

Cornell University in the field of plant science.