Preemergence herbicides are typically applied by broadcasting to the top of raised beds before laying the plastic mulch in plasticulture production systems. Broadleaf and grass emergence is limited to transplant holes in the mulch. As a result, most herbicides are applied under the mulch in locations where weeds cannot emerge and herbicides are unnecessary. To reduce this excessive off-target application, a precision hole-punch sprayer was developed at the University of Florida for use in plasticulture production systems. The technology facilitates the application of herbicides during the hole-punch operation immediately before transplant. Application of napropamide and S-metolachlor in an application volume of 233 L ha−1 of water using the precision hole-punch applicator had no effect on tomato and bell pepper growth and yield. Equipment accuracy ranged from 55% to 90%. Preemergence herbicide use was reduced by 88% to 92% with no reduction in weed control. The hole-punch applicator is an effective way to reduce PRE herbicide use in transplant vegetables grown using the plasticulture production system.

Field studies were conducted to determine the effect of metam sodium and S-metolachlor applied through drip irrigation on yellow nutsedge, common purslane, bell pepper, and tomato (injury and yield) in plasticulture. Treatments consisted of weed-free, weedy, S-metolachlor alone at 0.85 kg ha-1, methyl bromide, metam sodium (43, 86, 176, and 358 kg ai ha–1) alone, and metam sodium (43, 86, 176, and 358 kg ai ha–1) followed by S-metolachlor at 0.85 kg ha–1. Metam sodium and S-metolachlor was applied preplant 2 wk before and 2 wk after transplanting (WAT) through drip irrigation, respectively. No injury was observed to bell pepper and tomato from metam sodium alone, or metam sodium fb S-metolachlor treatments. With the exception of yellow nutsedge density 15 WAT in bell pepper, herbicide program did not influence yellow nutsedge and common purslane density at 4 and 6 WAT and bell pepper and tomato yield. At 15 WAT, yellow nutsedge density was lower in treatments that received metam sodium fb S-metolachlor compared to those treatments that only received metam sodium. Drip-applied metam sodium at 176 and 358 kg ha–1 in both bell pepper and tomato provided similar control of common purslane, and yellow nutsedge, produced comparable yields, and failed to elicit any negative crop growth responses when compared to MeBr. In conclusion, metam sodium at 176 and 358 kg ha–1 fb S-metolachlor 0.85 kg ha–1 is an effective MeBr alternative for season long weed control in plasticulture bell pepper and tomato.

Additive series studies were conducted under greenhouse conditions to determine the effects of nitrogen (N) rate and purple nutsedge densities on the yield of ‘California Wonder’ bell pepper. Initial densities of purple nutsedge were 0, 100, 200, and 300 plants/m2. Nitrogen was applied at 70, 140, and 210 kg/ha. Plants were allowed to interfere for 10 wk. There were significant purple nutsedge population density by N rate interactions on bell pepper fruit yield. At 70 kg N/ha, no significant effect of weed population densities was found on fruit yield, whereas at the rates of 140 and 210 kg N/ha there were significant nutsedge density effects. As N rates and nutsedge densities increased, so did purple nutsedge biomass. Linear regression models described the interference. Bell pepper fruit yield reduction was 73% at 210 kg N/ha with an initial nutsedge population density of 300 plants/m2.

Bell pepper is an economically important vegetable crop that is often impaired by weeds. Management of weeds in bell pepper is required to minimize yield loss because this crop does not tolerate weed competition. Several herbicides have been reported as selective for bell pepper, but research supporting their use for weed control in this crop is limited. Several herbicides were screened in a greenhouse to assess effects on plant biomass, and eight were selected that appeared to be safe for bell pepper. These herbicides, in addition to oxadiargyl, were then evaluated at two different Chilean locations, using different application timings. We measured the effects on plant injury, fruit yield, and the need for additional hand weeding on transplanted bell peppers. The herbicides clomazone, napropamide, pendimethalin, and S-metolachlor caused minimal foliar chlorosis and necrosis but did not affect fruit yield at either location. Pretransplant-incorporated application (PTI) caused no effect on fruit yield from the herbicides evaluated, whereas applications 2 wk (POST2) and 8 wk (POST8) after transplanting reduced fruit yield significantly. For weed management, the best combination was PTI + POST2 + POST8, which reduced the hand-weeding time by 30% compared to the control, at both locations. Based on our results, clomazone, pendimethalin, and S-metolachlor were the most effective treatments applied after transplanting, whereas all herbicides tested were selective for bell pepper when applied and incorporated before transplanting. Results presented here provide new insight into herbicides that can be used to manage weeds in bell pepper and shows that timing of herbicide application is critical to prevent injury to this crop.

Fomesafen and imazosulfuron are two recently registered herbicides for use in Florida bell pepper. Field studies were conducted in 2012 and 2013 to evaluate PRE, POST-directed (POST-DIR), and PRE followed by (fb) POST-DIR control programs utilizing these new herbicides for nutsedge control in Florida bell pepper. PRE treatments included: S-metolachlor at 0.71 and 1.07 kg ai ha−1, fomesafen at 0.28 and 0.42 kg ai ha−1, S-metolachlor at 0.71 kg ha−1 + fomesafen 0.28 kg ha−1, and S-metolachlor at 1.07 kg ha−1 + fomesafen at 0.42 kg ha−1. POST-DIR treatments included imazosulfuron at 0.21 and 0.34 kg ai ha−1. PRE fb POST-DIR treatments included S-metolachlor at 0.71 or 1.07 kg ha−1 fb imazosulfuron at 0.21 kg ha−1 and fomesafen at 0.28 or 0.42 kg ha−1 fb imazosulfuron at 0.21 kg ha−1. Nutsedge control in both years at 28 d after planting was similar among all PRE treatments providing ≤ 60% control. The addition of imazosulfuron POST-DIR following S-metolachlor or fomesafen PRE provided greater control compared to S-metolachlor or fomesafen alone 14, 21, and 28 d after the POST-DIR application. Plots treated with S-metolachlor resulted in lower marketable weight and marketable fruit count compared to fomesafen in 2012; however, this was not observed in 2013. The results for these studies indicate the importance of a PRE fb POST-DIR herbicide for nutsedge control and that fomesafen or S-metolachlor PRE fb imazosulfuron POST-DIR provides growers with a viable tool capable of achieving season-long control of nutsedge in bell pepper.

Drip irrigation is installed under polyethylene mulch to supply irrigation and nutrients to vegetables grown in plasticulture. This irrigation system also provides an alternative method for application of herbicides into the plant bed for control of yellow and purple nutsedge. Greenhouse and field studies were conducted to determine bell pepper tolerance to halosulfuron, imazosulfuron, and trifloxysulfuron applied POST (over the top of pepper in greenhouse study, POST-directed in the field study) or soil applied (applied by hand with water in greenhouse study or through drip irrigation in the field study). In greenhouse studies, pepper injury from halosulfuron, imazosulfuron, and trifloxysulfuron applied POST was similar at 14 and 21 d after treatment (DAT; 21 to 35% and 54 to 60%, respectively). Halosulfuron, imazosulfuron, and trifloxysulfuron soil applied in greenhouse studies caused 6 to 8% and 13 to 20% injury to pepper at 14 and 21 DAT, respectively. Pepper injury in greenhouse studies increased as rate of halosulfuron, imazosulfuron, and trifloxysulfuron increased regardless of application method (soil or POST applied). Dry pepper weight at 28 DAT followed an inverse linear response to increasing rates of halosulfuron, imazosulfuron, and trifloxysulfuron. In field studies, bell pepper height among herbicide treatments ranged from 32 to 37 cm at 14 DAT and was not different from the nontreated check (36 cm). Number one grade (7.8 to 14.7 MT ha−1) and fancy grade (2.1 to 2.8 MT ha−1) pepper fruit yield was not different in herbicide-treated pepper compared with yield of pepper in the nontreated check (10.0 to 26.6 MT ha−1, respectively). Based on these studies, pepper has excellent crop tolerance to halosulfuron, imazosulfuron, and trifloxysulfuron applied through drip irrigation or POST-directed but is not tolerant to POST applications.

Integrated management programs are becoming increasingly necessary for nutsedge control in the absence of methyl bromide. In 2012, field studies were established and maintained for a period of 2 yr at two locations to evaluate the additive effect of fallow programs and preplant fumigants for nutsedge control in bell pepper. The study included eight fallow programs consisting of eight combinations of glyphosate (G) and cultivation (C), and two fumigants; 1,3-dichloropropene + chloropicrin, dimethyl-disulfide + chloropicrin, and a nontreated check. All fallow programs provided greater late-season control of nutsedge compared to the nontreated, with the greatest control of nutsedge observed with glyphosate fb (followed by) glyphosate (GG) and glyphosate fb cultivation fb glyphosate (GCG) fallow programs. Fumigation provided additional nutsedge control in single-input fallow programs. Increased marketable yield was observed in 2012 with the application of either fumigant compared to a nonfumigated control. Furthermore, increased marketable yield was observed with more intensive fallow programs in 2013. Nutsedge control in bell pepper was significantly increased when a fallow program was used in combination with other weed-management practices.

Large crabgrass, redroot pigweed, and hairy galinsoga are three important weed species in bell pepper and other crops in the northeastern United States. Field experiments were conducted in 1998 and 1999 to determine the influence of density and relative emergence time of the three weed species on bell pepper fruit yield. Densities of 0, 1, 2, 4, 8, 16, and 32 plants m−1 row were established for each weed species from naturally occurring weed populations. The effects of relative emergence time were studied by investigating the different yield responses to weeds emerging at two different times: 3 d or 2 wk after transplanting of pepper. Both weed density and relative emergence time affected pepper yield loss. The relative competitive ability of weed species varied between years. Large crabgrass was the most competitive species in 1998 and the measure of yield loss at low weed densities, I, was estimated to be 34% on the basis of the nonlinear hyperbolic equation. Redroot pigweed was most competitive in 1999 with an estimate of 88% for I. Hairy galinsoga was the least competitive weed in both years. Maximum yield loss under 32 plants m−1 row ranged from 19% with late-emerging hairy galinsoga in 1998 to 99% with early-emerging redroot pigweed in 1999. A new equation was proposed to characterize the relation between yield loss and weed pressure by expanding the nonlinear hyperbolic equation to include a parameter to account for the change of maximum yield loss with emergence time. The expanded equation generally provided a more accurate prediction of yield loss. In addition, several models are introduced to describe both the effects of density and relative emergence time of multiple weed species on crop yield. Generally these models provided an adequate fit of the data and a good description of the competitive ability of the mixed population.