Weed management is consistently ranked among the top priorities of the United States sweetpotato industry. To provide additional weed and insect management strategies for sweetpotato, we initiated development of insect-resistant germplasm that also has weed tolerance by breeding and selecting for sweetpotato clones that are fast growing and have semi-erect to erect canopy architecture. Field studies were conducted in 2018 and 2019 in Charleston, South Carolina, to quantify the effects of weed-free interval and sweetpotato clone on weed counts for naturally occurring weed species, storage root yield, and insect resistance to the major pests of sweetpotato. Weed-free intervals included plots that were weedy all season and weed-free for 2, 3, and 4 wk after transplanting. Sweetpotato clones evaluated included ‘Beauregard’, ‘Covington’, ‘Monaco’, and six advanced selections with semi-erect to erect plant habit. Significant weed-free interval and sweetpotato clone main effects were observed for all variables measured, but not for their interaction. Two sweetpotato clones, USDA-17-037 and USDA-17-077, were consistent across both years and had the lowest weed counts, exhibited enhanced insect resistance, and were the highest yielding entries. These results demonstrate the potential for development of insect-resistant sweetpotato germplasm with a vigorous, erect plant habit that may be less susceptible to weed interference than cultivars with spreading shoot growth. The combination of germplasm that is both resistant to insect pests and competitive with weeds can provide organic and subsistence sweetpotato growers solutions to these critical issues related to sweetpotato production.

Purple nutsedge is a troublesome weed in tomato grown in plasticulture systems. Field trials were conducted in the fall of 2017 and spring of 2018 at Balm, FL, to evaluate multiple herbicide programs applied pretransplanting (pre-T), post-transplanting (post-T), and pre-T followed by (fb) post-T for purple nutsedge control in plasticulture tomato. Pre-T treatment of sulfentrazone or S-metolachlor alone were ineffective and did not decrease purple nutsedge density compared with the nontreated control. Post-T application of halosulfuron did not reduce purple nutsedge density at 12 wk after initial treatment (WAIT) in fall 2017 but reduced the purple nutsedge density at 17 WAIT in both seasons. Pre-T sulfentrazone or S-metolachlor application fb halosulfuron applied post-T were the most effective treatments and consistently reduced purple nutsedge population in both seasons. Herbicide treatments did not injure or reduce tomato height or yield. Overall, these results suggest sequential herbicide programs, including pre-T application of sulfentrazone or S-metolachlor fb post-T application of halosulfuron generally resulted in greater purple nutsedge control compared with pre-T or post-T application only. Halosulfuron applied post-T is critical to provide season-long purple nutsedge control in plasticulture 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.

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.

Greenhouse studies were conducted to evaluate halosulfuron tolerance of several squash and cucumber cultivars commonly grown in Georgia. There was an inverse linear relationship between squash plant biomass and rate of halosulfuron (r 2 = 0.70 to 0.92). With the exception of ‘Supersett’, the slopes from regression of all squash cultivars were equivalent. The estimated amount of halosulfuron required to reduce growth by 20%, based on regression, ranged from 8.2 to 45 g ai/ha (for Supersett and ‘Dixie’, respectively). Squash plant height was also reduced by halosulfuron, though plants began to recover from the injury by the end of the study. There was no effect of halosulfuron rate on cucumber plant biomass or height. Cucumber cultivars appeared to be more tolerant to halosulfuron than did squash cultivars.

Viable horseradish roots of various sizes remain in the soil after harvest and can develop into volunteer plants in subsequent crops. Experiments were conducted to evaluate POST herbicides on volunteer horseradish control and to determine if efficacy is dependent upon horseradish root segment size, herbicide rate, horseradish cultivar, or horseradish shoot size at application. In the greenhouse, horseradish root segment size did not affect herbicide efficacy. Chlorimuron, cloransulam, imazamox, (2,4-dichlorophenoxy)acetic acid (2,4-D) amine, halosulfuron, and imazethapyr plus imazapyr provided greater than 95% foliar control of volunteer horseradish. Chlorimuron, halosulfuron, and 2,4-D amine were also among the herbicides that provided the greatest reduction in horseradish root biomass (69% or greater). Glyphosate provided little foliar control (76%) and root biomass reduction (57%) after one application. The efficacy of 2,4-D amine on horseradish foliage and root biomass increased with increasing herbicide rate; however, the response of horseradish to halosulfuron was similar for all rates evaluated. Root biomass reduction of the horseradish cultivar ‘1573’ was less responsive to 2,4-D amine and halosulfuron applications compared with ‘1038’ and ‘1722’. However, foliar injury from 2,4-D amine and halosulfuron was less for the horseradish cultivar ‘1038’ compared with ‘1573’ and ‘1722’. In field studies, 2,4-D amine applied to 15- and 30-cm-tall horseradish and halosulfuron applied to 15-cm-tall horseradish resulted in the greatest foliar and root biomass reduction. This study indicated that in-season control of volunteer horseradish in rotational crops may be achieved through proper herbicide selection.

Nutsedge control is challenging in commercial vegetable production in the absence of methyl bromide, and therefore, an effective alternative is needed. This study investigated allyl isothiocyanate (ITC) as a methyl bromide alternative for purple nutsedge control under polyethylene-mulch. Greenhouse experiments were conducted to compare the retention of allyl ITC in treated soil (3,000 nmol g−1) under low-density polyethylene (LDPE) and virtually impermeable film (VIF) mulches. Field experiments were conducted to evaluate the effectiveness of allyl ITC (6 rates: 0, 15, 75, 150, 750, 1500 kg ai ha−1) under VIF mulch against purple nutsedge. Additionally, a standard treatment of methyl bromide+chloropicrin (67 : 33%) at 390 kg ai ha−1 under LDPE mulch was included for comparison. In the greenhouse experiment, the predicted half-life of allyl ITC under LDPE and VIF mulch was 0.15 and 0.59 d, respectively. In the field experiment, it was predicted that allyl ITC at 1,240 and 1,097 kg ha−1 under VIF mulch is required to control purple nutsedge shoot and tubers equivalent to methyl bromide + chloropicrin at 4 wk after treatment (WAT). It is concluded that allyl ITC under VIF mulch would need to be applied at 2.8 to 3.2 times the standard treatment of methyl bromide + chloropicrin under LDPE mulch for commercially acceptable purple nutsedge control.