James P. Gilreath

Season-Long Interference of Yellow Nutsedge (Cyperus esculentus) with Polyethylene-Mulched Bell Pepper (Capsicum annuum)1

Yellow nutsedge, a weed commonly present in Florida vegetable fields, may substantially reduce crop yields when not controlled. Soil fumigation with methyl bromide effectively controls nutsedges, but methyl bromide is being phased out of production and use in the United States. Therefore, nutsedge management in bell pepper is a cause for concern. An experiment was conducted during four seasons (spring and fall of 1999 and 2000) to determine the tolerance of bell pepper grown at two in-row spacings (23 and 31 cm) to interference resulting from planted yellow nutsedge tuber densities (0 to 120 tubers/m2). Relative to yields with no nutsedge, pepper fruit yields in each season were reduced 10% with fewer than 5 planted tubers/m2. Yield losses increased more rapidly with an increase in initial nutsedge density from 0 to 30 than from 30 to 120 tubers/m2. With 30 nutsedge tubers/m2, large fruit yield was reduced 54 to 74% compared to that with no nutsedge. Nutsedge shoots overtopped the pepper plants as early as 6 wk after treatment when, with 15 planted tubers/m2, nutsedge interference reduced pepper plant biomass by 10 to 47%. In the absence of methyl bromide, weed control strategies with high efficacy against yellow nutsedge will be needed for bell pepper production. Nomenclature: Methyl bromide; yellow nutsedge, Cyperus esculentus L. #3 CYPES; bell pepper, Capsicum annuum L. ‘X3R Camelot’. Additional index words: Weed interference, yellow nutsedge competition, yield loss. Abbreviations: No., number; WAT, weeks after treatment.

Efficacy of methyl bromide alternatives on purple nutsedge (Cyperus rotundus) control in tomato and pepper

Field trials were conducted to compare the effect of various soil fumigants along with in-bed pebulate and row-middle metribuzin applications on purple nutsedge control and on tomato and bell pepper growth and yield. Treatments consisted of combinations of soil fumigants, pebulate, and metribuzin. Fumigants levels were (1) untreated control, (2) methyl bromide (MBr) + chloropicrin (Pic) (67 + 33%, respectively), (3) Pic, (4) metham, (5) dazomet, and (6) 1,3-dichloropropene (1,3-D) + Pic (83 + 17%, respectively). Pebulate levels were either applied in-bed or not applied. Row middles were either sprayed with metribuzin or untreated. In both crops, purple nutsedge populations were independently influenced by fumigants and pebulate applications, with the highest number of purple nutsedge plants in the untreated control. The addition of pebulate reduced purple nutsedge populations in all treatments. In tomato trials, the yield was affected by fumigants, with the highest losses (53 and 50% reductions in fruit number and weight) observed in the nonfumigated control. In pepper trials, fruit number and weight were individually influenced by fumigants and metribuzin sprayings. Application of metribuzin to row middles increased yields 10% relative to nontreated plots. Nomenclature: Purple nutsedge, Cyperus rotundus L. #3 CYPRO; pepper, Capsicum annuum L.; tomato, Lycopersicon esculentum Mill. Additional index words: Chloropicrin, dazomet, 1,3-dichloropropene, interference, metham, metribuzin, pebulate, soil fumigants. Abbreviations: 1,3-D, 1,3-dichlopropene; MBr, methyl bromide; Pic, chloropicrin; WAT, weeks after transplanting.

Efficacy of 1,3-Dichloropropene Plus Chloropicrin in Combination with Herbicides on Purple Nutsedge (Cyperus rotundus) Control in Tomato1

A study was conducted to compare the effect of 1,3-dichloropropene (1,3-D) + chloropicrin (Pic) in a 83:17 ratio (C-17) used alone or in combination with herbicides on tomato. Treatments evaluated included 1,3-D (325 kg ai/ha) plus Pic (67 kg ai/ha) used either alone or with pebulate (4.5 kg ai/ha), napropamide (4.5 kg ai/ha), metolachlor (1.1 and 2.3 kg ai/ha), lactofen (2.3 kg ai/ha), or flazasulfuron (0.4 kg ai/ha). Pebulate was consistently more effective in controlling purple nutsedge than the other herbicides tested. Purple nutsedge was more effectively controlled with C-17 in combination with pebulate than with the fumigant alone. Shallow incorporation of pebulate failed to improve weed control and tomato fruit yield. Nomenclature: Chloropicrin; 1,3-dichloropropene; flazasulfuron; lactofen; metolachlor; napropamide; pebulate; purple nutsedge, Cyperus rotundus L. #3 CYPRO; tomato, Lycopersicon esculentum Mill. ‘Solar Set’. Additional index words: Flazasulfuron, lactofen, methyl bromide, metolachlor, napropamide, pebulate, soil fumigant. Abbreviations: C-17, 1,3-D + Pic (87:13); 1,3-D, 1,3-dichloropropene; MBr, methyl bromide; Pic, chloropicrin; WAT, weeks after treatment.

Phytotoxic Effects of Glyphosate on Pepper (Capsicum annuum)1

Abstract: Glyphosate was applied to pepper as single or sequential applications to assess the consequences of drift or other accidental exposures. Foliar injury increased and plant vigor declined with increased rates of glyphosate and were exacerbated by a second application. Single applications at flowering (stage 1) were more damaging than single applications after fruit set (stage 2). Decline in marketable yield with increased glyphosate rate was greater with stage 1 applications, except in spring 1987 when marketable yields with single applications of glyphosate at stage 1 or stage 2 were statistically similar. Sequential applications resulted in the lowest marketable yields. Total yields declined with increased glyphosate rate and decline was more pronounced with sequential applications than with single applications. Total yield was affected to a greater extent when glyphosate was applied at stage 1 than at stage 2. Yield was more sensitive to two successive exposures than to single applications. Mean fruit weight was reduced by glyphosate in two of the four experiments. Nomenclature: Glyphosate; pepper, Capsicum annuum L. Additional index words: Simulated drift, herbicide injury. Abbreviations: DAT, days after treatment; WAT, weeks after treatment.

Weed Management with Oxyfluorfen and Napropamide in Mulched Strawberry

Two trials were conducted to evaluate the effects of herbicide and mulch on weed management and strawberry yield. Napropamide at rates of 4.50, 6.75, or 9.00 kg ai/ha; oxyfluorfen at 0.57 kg ai/ha; and napropamide plus oxyfluorfen at 4.50 plus 0.57 kg/ha were applied pretransplant on pressed beds covered with either low-density polyethylene mulch or virtually impermeable film. There was no herbicide by mulch interaction. Mulch types had no influence on weed counts and fruit yield, whereas herbicides affected both variables. The napropamide plus oxyfluorfen treatment resulted in the highest fruit number and weight, increasing yield by 20% with respect to the nontreated control. This herbicide combination provided the best weed suppression. Nomenclature: Napropamide; oxyfluorfen; strawberry, Fragaria × ananassa Duch. Additional index words: Acetamides, crabgrass, diphenylethers, interference, mulch, primrose, ragweed. Abbreviations: GCREC, Gulf Coast Research and Education Center; WAP, weeks after planting.

Purple Nutsedge (Cyperus rotundus) Control with Fumigant and Pebulate Combinations in Tomato1

Field trials were conducted to determine the effect of fumigant-pebulate combinations on purple nutsedge density in fresh market tomato. Treatments consisted of methyl bromide plus chloropicrin (MBr plus Pic) [67:33] at rates of 270 and 130 kg/ha, respectively; Pic plus pebulate at 400 and 4.5 kg/ha, respectively; metham (MNa) plus pebulate at 485 and 4.5 kg/ha, respectively; dazomet plus pebulate at 950 and 4.5 kg/ha, respectively; and 1,3-dicholopropene plus Pic (C-17) [87:13] plus pebulate at 392 and 4.5 kg/ha, respectively. At 12 wk after treatment, MBr plus Pic controlled purple nutsedge more effectively (10 plants/m2) than the fumigant-pebulate combinations (50 to 70 plants/m2). Compared to MBr plus Pic, Pic plus pebulate had a 14% lower marketable yield. No differences in marketable yield were noted with dazomet plus pebulate or C-17 plus pebulate compared to MBr plus Pic. However, MNa plus pebulate produced a 15% higher yield than MBr plus Pic. Additionally, MNa plus pebulate had 15% higher marketable fruit weight than MBr plus Pic. Nomenclature: Purple nutsedge, Cyperus rotundus L. #3 CYPRO; tomato, Lycopersicon esculentum Mill. ‘Sunny’. Additional index words: Methyl bromide, chloropicrin, metham, dazomet, 1,3-dichloropropene. Abbreviations: MBr, methyl bromide; MNa, metham; 1,3-D, 1,3-dichloropropene; Pic, chloropicrin; C-17, 1,3-D plus Pic (87:13); MITC, methylisothiocyanate; WAT, weeks after treatment.

Phosphorus absorption in lettuce, smooth pigweed (Amaranthus hybridus), and common purslane (Portulaca oleracea) mixtures

Abstract Greenhouse studies were conducted to determine the influence of phosphorus (P) concentrations on the growth of lettuce, smooth pigweed, and common purslane in monocultures and in mixtures and to determine the P-absorption rate of each species over time. For the P-competition studies, lettuce–smooth pigweed and lettuce–common purslane mixtures were established in P-less hydroponic solutions. Each lettuce–weed mixture was established separately. Concentrations of P were 10, 20, 40, 80, and 160 mg L−1. Lettuce to weed planting proportions were 2:0, 0:2, and 1:1. In the mixtures, biomass of common purslane increased sharply between 10 and 20 mg P L−1, depressing lettuce growth. No biomass changes were observed in smooth pigweed as P concentration increased. However, both weeds increased their P content within this range, depriving lettuce of this nutrient. Common purslane competed for P for its own growth, whereas smooth pigweed absorbed P luxuriously. For the P-absorption studies, roots of lettuce, smooth pigweed, and common purslane plants were submersed in a 20 mg P L−1 solution for 1, 2.5, 5, 10, 20, 40, 60, 90, 180, 360, 720, and 1,440 min. Common purslane was shown to be the most aggressive species for the nutrient, absorbing 50% of the content in 295 min, whereas lettuce and smooth pigweed needed 766 and 825 min to absorb 10 mg P L−1. Nomenclature: Common purslane, Portulaca oleracea L. POROL; smooth pigweed, Amaranthus hybridus L. AMACH; lettuce, Lactuca sativa L.

Development of a production system for weeds as biomass crops

Abstract This paper describes the methodology involved in the selection of several weed species for the production of bioenergy feedstocks and the development of production systems for these species. Five species were selected for evaluation from an initial 11 species. Response to low inputs of nitrogen (N) and potassium (K), regrowth from overwintered crowns, and vegetative propagation were studied. Application of 56 kg ha −1 of N resulted in dry matter yields of 7·2, 36·1, 33·7, 16·3 and 10·9 Mg ha −1 for Baccharis sp., Eupatorium capillifolium, Sida rhombifolia, Amaranthus hybridus and Ricinus communis , respectively. Greater than 70% regrowth was observed for overwintered crowns of E. capillifolium, Baccharis sp. and Sida rhombifolia plants. Softwood tip cuttings of all species, except R. communis , initiated roots. Only A. hybridus benefited significantly from application of rooting hormones.

Seasonal Variation of Paraquat Photodegradation Rate on Polyethylene Mulch

Field studies were conducted to determine the effect of season of the year, sunlight exposure time, and mulch color on paraquat photodegradation rate on polyethylene mulch. Experiments were established in winter, spring, and summer, with white and black polyethylene mulch, and paraquat-applied films were exposed to sunlight for 1, 4, 8, 24, 30, 48, 72, or 96 h after herbicide application. There was significant effect of the season by mulch color by time of exposure interaction on paraquat concentration recovered from mulch eluants. Winter paraquat photodegradation was lower than during the other seasons. At 48 h of sunlight exposure, predicted photodegradation on white mulch was 67, 83, and 88%, during winter, spring, and summer, respectively, whereas these values were 66, 82, and 84% on black mulch. The difference in paraquat photodegradation in winter with respect to the other seasons may be attributed to reduced ultraviolet radiation in winter, when solar radiation has to penetrate a larger atmosphere mass. In practical terms, transplanting on paraquat-applied mulch requires a minimum of 96 h during the spring and summer seasons, when concentrations were 5% or less, whereas a longer waiting period might be necessary in the winter. Nomenclature: Paraquat; tomato, Lycopersicon esculentum Mill. Additional index words: Tomato, Lycopersicon esculentum, herbicide breakdown, ultraviolet radiation.

Effects of Phosphorus Fertilization on Common Lambsquarters (Chenopodium album) Duration of Interference in Lettuce (Lactuca sativa) 1

Field trials were carried out in organic soils to determine the effects of different phosphorus (P) fertilization programs and common lambsquarters duration of interference on lettuce. Phosphorus was either banded (125 kg/ha) or broadcast (250 kg/ha) before lettuce planting. A common lambsquarters population density of four plants per 6 m row interfered with ‘South Bay’ lettuce for 2, 4, 6, or 8 wk after lettuce emergence, along with a weed-free control. For banded P, lettuce fresh weight declined linearly (y = 14.82 − 0.97x; r2 = 0.96) as duration of common lambsquarters interference increased. The effect of broadcast P over common lambsquarters duration of interference fit a quadratic equation (y = 10.67 − 1.69x + 0.12x2; r2 = 0.98). The difference in the regression model intercepts for both P fertilization programs showed that in the absence of common lambsquarters interference, marketable lettuce fresh weight was higher by banding P than by broadcasting P. Based on predicted values, this difference is approximately 28% (+4.15 kg per 6 m row) in favor of banded P. Therefore, banding P at 125 kg/ha proved to be beneficial in raising lettuce fresh weight regardless of the duration of interference. For banded P, the model predicts that 10% yield reduction would be observed at 1.53 wk (10.5 d) of common lambsquarters interference. However, with broadcast P, this period declined to 0.67 wk (4.7 d). Nomenclature: Common lambsquarters, Chenopodium album L. #3 CHEAL; lettuce, Lactuca sativa L. Additional index words: Competition, cultural weed control, integrated weed management, nutrients.