The response of pepper varieties to Egyptian broomrape and nodding broomrape was characterized in comparison with tomatoes grown in pots and in aqueous solution, according to two criteria: 1. germination of the parasite's seeds in the presence of the host roots; and 2. the number of parasites per host plant. More than 50% of Egyptian broomrape seeds germinated in the presence of all pepper variety roots except the sweet pepper Maor. However, only a few attached and developed. The two paprika varieties Lehava and Shani were hosts to more parasites than the sweet pepper varieties, and showed as many as 15 parasites per host plant. In contrast, tomato roots induced less then 10% seed germination but were highly susceptible to the parasite (30 parasites per host plant). Damage caused to pepper foliage and fruit was not significant, compared to the heavy damage caused to tomato. Pepper roots stimulated germination of 22 to 26% of nodding broomrape seeds but without the formation of parasitic attachments, whereas tomato roots stimulated germination of less than 10% of the seeds but the plants were then heavily damaged by the parasite. Interplanting of tomato with pepper in nutrient solution did not change the amount of Egyptian broomrape parasites on pepper, hut a fourfold increase in the number of nodding broomrape was observed on tomato roots, compared to the number of parasites on tomato roots when planted without pepper.

The sensitivities of tobacco, tomato, pepper, and cucumber seedlings to an aquatic herbicide, fluridone, were examined in growth chamber and greenhouse studies. New leaves of tobacco seedlings became chlorotic after 6-d exposure to fluridone concentrations of 5 μg/L or greater in hydroponic float culture, and dry weights were significantly reduced at 100 μg/L or greater. When treated only once at the beginning of a 2-wk evaluation period, all crops except cucumber exhibited injury symptoms at 100 μg/L. When grown in sand, pepper and tomato were injured at 25 μg/L; tobacco injury occurred at 10 μg/L. Dry weights of pepper, tobacco, and tomato seedlings decreased significantly at 250, 50, and 250 μg/L, respectively, on potting mix; effects on dry weights were not significant for plants on sand. Cucumber was injured by treatment at 100 μg/L or greater in sand, but there were no effects on dry weights in either sand or potting mix. When treated three times weekly for 2 wk with fluridone, pepper, tobacco, and tomato grown in potting mix were injured by 50, 25, and 100 μg/L; when grown in sand, injury occurred at 10, 5, and 10 μg/L, respectively. Dry weights of pepper, tobacco, and tomato were reduced by 50,50, and 100 μg/L, respectively, in potting mix; effects on dry weights were not significant for plants in sand. Cucumber seedlings were damaged by 250 μg/L or higher on potting mix and 100 μg/L or higher on sand, but there were no effects on dry weights regardless of substrate. Threshold injury levels for plants grown in potting mix to the second true leaf stage and then treated three times weekly were 25 μg/L for pepper and tobacco and 50 μg/L for tomato; dry weights were significantly reduced in pepper at 25 μg/L and in tobacco and tomato at 50 μg/L. Cucumber seedlings were not injured by any treatment in this test.

We are studying the possibility of altering the virulence and host range of a phytopathogen by transferring and expressing certain genes from the soil-dwelling saprophyte, Streptomyces hygroscopicus, in a plant pathogen model, Xanthomonas campestris pv. campestris (XCC). The genes, referred to herein as the “bialaphos genes,” encode the production of bialaphos, a potent glutamine-synthetase-inhibiting herbicide. This cluster of genes was originally isolated from several biosynthetically blocked mutants of S. hygroscopicus and constructed into a plasmid vector, pBG9. We have transferred a fragment of the gene cluster into pLAFR3, a plasmid that functions in both Escherichia coli and XCC and contains a tetracycline resistance marker. The resulting plasmid, named pIL-1, was used to transform E. coli and was incorporated into XCC by conjugation. The transfer of the fragment was confirmed by Southern analysis. The genes were maintained in XCC for about 47 generations in the absence of selection for tetracycline, and no changes in cultural phenotypes were seen in the transformed XCC (XCC/pIL-1). The XCC/pIL-1 cells were pathogenic to their natural hosts cabbage and broccoli, but induced an altered hypersensitive response in the nonhosts bean, pepper, sunflower, and tobacco. The pathogenic host-reaction, induced by the parent XCC, XCC/pLAFR3, and XCC/pIL-1, was a typical black rot disease in inoculated leaves of the two hosts. The nonhost reaction on the nonhost leaves was necrotic hypersensitivity, induced by XCC and XCC/pLAFR3, or the inhibition of hypersensitivity accompanied by only chlorosis at sites inoculated with XCC/pIL-1. We hypothesize that the altered hypersensitivity phenotype may be due to the transformed XCC becoming more compatible with the nonhosts, a step toward acquiring nonhost-virulence, or due to disruption of the normal expression of the hypersensitivity and pathogenicity genes in the transformed XCC. More work is needed to confirm that the introduced genes are being expressed in XCC. With further understanding, this approach may provide a useful model to study host range, virulence, and strain improvement of plant pathogens for biological control of weeds.

Tolerance of direct-seeded pepper under clear plastic mulch to herbicides applied pre- and post-emergence was investigated in 1991 and 1992. Weed control of herbicides applied preemergence was also studied. Paprika cultivar ‘Buketen’ and canning cultivars ‘Piquillo de Lodosa’ and ‘Pico de Mendavia’ were seeded in the field in Zaragoza, Spain, in a loamy soil. Percent emergence, plant mortality after the postemergence treatment, dry weight of plants, and fruit weight were recorded. Pepper was tolerant to diphenamid and napropamide applied preemergence but these herbicides did not control broadleaf weeds. Clomazone, when applied preemergence resulted in chlorotic seedlings and at 2 kg ai/ha reduced the final stand, but was selective when applied at the 6 to 8-leaf stage of the crop. Pepper was tolerant to diethatyl-ethyl when applied preemergence. However, diethatyl-ethyl applied postemergence caused severe phytotoxicity symptoms, and when mixed with diphenamid, fruit ripeness in 1992 was delayed. Weed control during the crop emergence period was better when diethatyl-ethyl was used mixed with diphenamid or napropamide.

The effect of soil residues of flumetsulam plus clopyralid on several vegetable crops grown in rotation with field corn was investigated over 2 yr. The effect of soil residues of flumetsulam plus clopyralid on sweet corn cultivars of varying sensitivity to acetolactate synthase (ALS)-inhibiting herbicide was also investigated. Flumetsulam plus clopyralid was applied preemergence (PRE) to field corn at 0, 50 + 135, and 100 + 270 g ai/ha, respectively, in 1993 and 1994. Cucumber, tomato, cabbage, potato, pepper, pea, and sweet corn were planted each spring, both 1 and 2 yr following the herbicide application. Cabbage was very sensitive and showed visible injury symptoms and yield reductions both years following flumetsulam plus clopyralid application. Pepper showed a yield reduction only in 1995. All other crops showed no injury or yield reductions. Flumetsulam plus clopyralid was applied PRE and postemergence (POST) to six sweet corn cultivars in 1995. These six sweet corn cultivars were replanted into the same site 1 yr later. Flumetsulam plus clopyralid severely injured three of six sweet corn cultivars in 1995, the year of application. Soil residues 1 yr later, however, did not injure or reduce yield of any sweet corn cultivars, including cultivars sensitive to ALS-inhibiting herbicides.

Additive series experiments were conducted under greenhouse conditions to determine the effect of season-long interference of different initial population densities of purple nutsedge on the shoot dry weight and fruit yield of tomato and bell pepper. Purple nutsedge densities up to 200 plants/m2 linearly reduced shoot dry weight at flowering and fruit yield of both crops as weed density increased. Both variables were directly correlated, and for each percentage unit of tomato shoot dry weight loss at flowering, fruit yield was reduced 1.24 units, whereas for bell pepper this relationship was 1 to 2.01. Total shoot and tuber biomass of purple nutsedge increased as density increased. The presence of either crop caused a decline in the total shoot dry weight accumulation of purple nutsedge, with tomato producing a higher degree of loss than bell pepper to the weed. Fruit yield losses due to purple nutsedge interference reached 44% for tomato and 32% for bell pepper.

Two field studies were conducted to compare bentazon tolerance in “Bohemian Chili” (BCH) and “Keystone Resistant Giant” (KRG) with other pepper cultivars and plant introductions (PIs). In the first study, BCH, KRG, “Santaka” (SA), and “Sweet Banana” (SB) were treated with five rates of bentazon from 1.1 to 9.0 kg ai/ha. Based on foliar injury, the cultivars ranked BCH = SA < KRG < SB; based on yield tolerance to bentazon, they ranked KRG ≤ SB < SA ≤ BCH. In the second study, the response of BCH, KRG, SA, SB, and five PIs to 4.5 kg/ha bentazon showed that 3 PIs (127445, 163187, 246123) tolerated bentazon similarly to BCH and SA.

Abrasive weed control is a novel weed management tactic that has great potential to increase the profitability and sustainability of organic vegetable cropping systems. The objective of this study was to determine the effect of air-propelled organic abrasive grits (e.g., organic fertilizers) on weed seedling emergence and growth and vegetable crop growth. A series of thirteen greenhouse trials were conducted to determine the susceptibility of weeds to abrasive weed control with one of six organic materials including: corn cob grits, corn gluten meal, greensand fertilizer, walnut shell grits, soybean meal, and bone meal fertilizer. In addition, crop injury was quantified to determine the potential utility of each organic material as abrasive grits in tomato and pepper cropping systems. Of the six organic materials, corn gluten meal, greensand fertilizer, walnut shell grits, and soybean meal provided the broadest range of POST weed control. For example, one blast of corn gluten meal and greensand fertilizer reduced Palmer amaranth (one-leaf stage) seedling biomass by 95 and 100% and green foxtail (one-leaf stage) biomass by 94 and 87%, respectively. None of the organic materials suppressed weed seedling emergence when applied to the soil surface, suggesting that residual weed control with abrasive grits is unlikely. Tomato and pepper stems were relatively tolerant of abrasive grit applications, though blasting with select materials did increase stem curvature in tomato and reduced biomass (corn cob grit) and relative growth rate (corn gluten meal and greensand) in pepper. Results suggest that organic fertilizers can be effectively used as abrasive grits in vegetable crops, simultaneously providing weed suppression and supplemental crop nutrition. Field studies are needed to identify cultural practices that will increase the profitability of multifunctional abrasive weed control in organic specialty crops.

Fresh market pepper and tomato are important crops in Florida. Production primarily occurs on raised beds covered with plastic mulch. Weeds emerging between the rows are often controlled with multiple applications of burndown and soil-residual herbicides. Crop damage attributed to root uptake of herbicides applied between the rows has been reported. An experiment was conducted in a greenhouse at the Gulf Coast Research and Education Center to examine the effect of root uptake of paraquat and paraquat tank-mixed with flumioxazin on pepper and tomato growth and yield. Herbicides were applied via subsurface irrigation at 0.0625×, 0.125×, 0.25×, 0.5×, 1×, 2×, 4×, 8×, and 16× labeled rates. The 1× rate was based on the estimated label rate that would be applied per plant in the field and was 0.122 g ai plant−1 (1,542 g ai ha−1) and 0.011 g ai plant−1 (143 g ai ha−1) for paraquat and flumioxazin, respectively. Root uptake caused necrosis of the veins, followed by complete tissue death at higher rates. The percentage of crop damage increased with herbicide rate for both species (P < 0.0001), with greater damage observed at the lower rates with the tank mix than with the paraquat alone. A reduction in shoot biomass and fruit yield of both crops was observed following root uptake. These results suggest that uptake of paraquat or paraquat tank-mixed with flumioxazin by pepper and tomato roots in a field situation is possible.

Cultivation is a critical component of organic weed management and has relevance in conventional farming. Limitations with current cultivation tools include high costs, limited efficacy, and marginal applicability across a range of crops, soil types, soil moisture conditions, and weed growth stages. The objectives of this research were to compare the weed control potential of two novel tools, a block cultivator and a stirrup cultivator, with that of a conventional S-tine cultivator, and to evaluate crop response when each tool was used in pepper and broccoli. Block and stirrup cultivators were mounted on a toolbar with an S-tine sweep. In 2008, the tripart cultivator was tested in 20 independently replicated noncrop field events. Weed survival and reemergence data were collected from the cultivated area of each of the three tools. Environmental data were also collected. A multivariable model was created to assess the importance of cultivator design and environmental and operational variables on postcultivation weed survival. Additional trials in 2009 evaluated the yield response of pepper and broccoli to interrow cultivations with each tool. Cultivator design significantly influenced postcultivation weed survival (P < 0.0001). When weed survival was viewed collectively across all 20 cultivations, both novel cultivators significantly increased control. Relative to the S-tine sweep, the stirrup cultivator reduced weed survival by about one-third and the block cultivator reduced weed survival by greater than two-thirds. Of the 11 individually assessed environmental and operational parameters, 7 had significant implications for weed control with the sweep; 5 impacted control with the stirrup cultivator, and only 1 (surface weed cover at the time of cultivation) influenced control with the block cultivator. Crop response to each cultivator was identical. The block cultivator, because of its increased effectiveness and operational flexibility, has the potential to improve interrow mechanical weed management.

Studies were conducted in 1996 and 1997 to determine the effect of irrigation systems used to produce transplants on subsequent tolerance of banana and bell pepper (Capsicum annuum) transplants to field-applied herbicides. The irrigation systems were overhead (OH), ebb and flood (EF), and float (F). At 2 and 4 wk, banana and bell pepper injury was greatest from clomazone (1.1 kg/ha) treatments. Banana and bell pepper yield were not influenced by herbicide treatment. Although crop injury was greater in 1997, there was no herbicide or irrigation system interaction with year. OH and EF irrigated banana pepper and OH irrigated bell pepper produced the greatest total yield over two harvests, whereas F irrigated pepper yielded the least. F irrigated bell pepper plants had reduced early total yield and fancy fruits relative to other irrigation treatments. F irrigated plants yielded 32 and 22% less than OH irrigated plants in banana and bell pepper, respectively. Stand counts at 3 wk after planting (WAP) show that, unlike OH and EF treatments, F treatments lost 240 to 330 plants/ha. Differences in stand among treatments were greater in 1997 than 1996. Based on our study, the OH irrigated system appears to be the best system for producing bell pepper transplants with the greatest total yield. With banana pepper, both OH and EF irrigated systems appear to produce banana pepper transplants with the greatest total yield. Also, pepper transplant tolerance to herbicides is not affected by the irrigation system used to produce transplants.

The effect of CGA 152005 residues in the soil on six crops grown in rotation with field corn was investigated over a 2-yr period. CGA 152005 at 10, 15, 20, and 30 g ai/ha was applied postemergence (POST) to corn in 1994. CGA 152005 at 15 and 30 g ai/ha, atrazine at 1,000 g ai/ha, CGA 152005 at 15 g plus atrazine at 500 g ai/ha, and CGA 152005 at 30 g plus atrazine at 1,000 g ai/ha were applied POST to corn in 1995. Soybean, pea, cabbage, tomato, pepper, and potato were planted each spring, 1 yr after herbicide application. Cabbage exhibited injury and yield reductions that increased with increasing application rate, and pepper exhibited slight injury at the highest rate and yield reduction in 1995. Cabbage yields were reduced by CGA 152005 plus atrazine, and tomato yields were reduced by CGA 152005 and CGA 152005 plus atrazine in 1996. Yields of other crops were not affected in either year.

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.

Vinegar can supplement the existing intrarow weed control options of organic farmers. However, there are two primary limitations to its use in vegetable crops. First, it is costly. Second, vinegar applications that contact the crop can cause injury and yield loss. The aim of this research was to use vinegar to control intrarow weeds in bell pepper and broccoli in a way that product costs would be reduced and crop injury would be minimized. Banded applications were shielded and directed below the crop canopy to reduce weed control costs and minimize contact with crop foliage. Organic paints applied to crop stems were evaluated as potential physical barriers to crop stem injury. Four field trials were conducted in 2009, two in transplanted bell pepper and two in transplanted broccoli. A single application of 200-grain vinegar (20% acetic acid) at 700 L ha−1 was applied when weeds were in the cotyledon to six-leaf stage. Applications were made to crops with the lower stems coated in one of two stem protectants, or left uncoated. Hand-weeded and weedy treatments were included for comparison. One day after vinegar application, in-row weed control was 100% in both pepper trials and greater than 96% in the broccoli trials. Two weeks after application, 75% fewer weeds germinated in the vinegar-treated areas compared with the areas that were hand weeded. Neither stem protectant prevented crop injury. Despite pepper foliar injury of less than 5%, stem injury 2 wk after application contributed to a measurable yield reduction. Broccoli injury was limited to instances where overspray contacted the crop canopy. With vinegar, high levels of weed control and the extended duration of that control relative to hand weeding could facilitate improved organic intrarow weed control. However, crop injury must be reliably reduced. Alternative stem protectants may merit evaluation.

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.