Field studies were conducted at two locations in 1997 and 1998 to evaluate crop injury, weed control, yield, and net economic returns of single and sequential postemergence applications of labeled and reduced rates of glyphosate to no-till, glyphosate-resistant soybean planted in narrow rows. Sequential applications provided at least 91% control of giant foxtail, while single applications provided at least 86% control with labeled rates and 68–93% control with reduced rates. Common waterhemp control was slightly higher with sequential vs. single treatments and with labeled rates vs. reduced rates. Velvetleaf control was greater than 96% with all treatments. Common cocklebur control was 90% or higher with all treatments except a single application of glyphosate at 210 g/ha. Lower control of giant foxtail and common waterhemp with single-application, reduced-rate treatments in two of the four trials resulted in lower yields. Overall, sequential applications, regardless of rate, provided greater weed control, yield, and net income and lower coefficients of variation (C.V.s) of net income than reduced-rate single applications. Single-application treatments showed a trend of decreased weed control, yield, and net income and higher C.V.s of net income with reduced rates of glyphosate.

Field trials were conducted at two sites in both 1997 and 1998 to evaluate soybean response and weed control with glufosinate alone or combined with quizalofop, lactofen, imazethapyr, flumiclorac, or bentazon plus acifluorfen in narrow-row, glufosinate-resistant soybean. Soybean injury ranged from 0 to 21% at 2 wk after treatment (WAT) and from 0 to 5% by 4 WAT. Glufosinate alone at 0.29 and 0.4 kg ai/ha controlled velvetleaf, common waterhemp, common ragweed, morningglory species, and giant foxtail greater than 85% in all studies. Mixtures containing glufosinate and other herbicides controlled these species greater than 81% but did not improve control over glufosinate alone. Estimates of weed biomass closely reflected visual control evaluations. However, giant foxtail biomass was higher for mixtures of glufosinate plus lactofen, flumiclorac, or bentazon and acifluorfen, indicating possible antagonism of glufosinate activity. At both locations, soybean yields were similar among most treatments, but that of the glufosinate plus lactofen treatment was lower when compared with other treatments. Additional trials evaluated soybean response and weed control with a preemergence herbicide followed by glufosinate postemergence (POST), glufosinate applied once or twice POST, and mixtures of glufosinate plus imazethapyr or flumiclorac POST in wide-row soybean. Glufosinate applied twice controlled common waterhemp, morningglory species, prickly sida, common cocklebur, and giant foxtail up to 39% greater than did glufosinate applied once. The addition of imazethapyr, but not flumiclorac, to glufosinate improved weed control when compared with glufosinate alone.

Field experiments were conducted at four locations (Larissa, Halkidona, Thessaloniki, and Halastra) in Greece to evaluate weed and cotton response to various pyrithiobac rates applied preplant incorporated (PPI), preemergence (PRE), or postemergence (POST). Pyrithiobac applied PPI or PRE at 0.068, 0.102, or 0.136 kg ai/ha controlled black nightshade, pigweeds, and common purslane at Larissa. However, pyrithiobac applied PRE at Thessaloniki and Halkidona was more effective against black nightshade and pigweeds than pyrithiobac applied PPI. Pyrithiobac applied PPI or PRE at 0.068 or 0.102 kg/ha did not control common lambsquarters at Thessaloniki. Weed control with trifluralin plus fluometuron applied PPI and alachlor plus fluometuron applied PRE at Larissa was slightly lower than that obtained with pyrithiobac. At Halkidona, trifluralin plus fluometuron applied PPI and alachlor plus fluometuron applied PRE provided weed control similar to that obtained with pyrithiobac. But at Thessaloniki, these treatments provided better weed control than pyrithiobac. Furthermore, pyrithiobac applied early postemergence (EPOST), midpostemergence, or in sequential systems controlled black nightshade and pigweeds, but it resulted in fair to good control of common purslane, velvetleaf, and common cocklebur. None of the POST treatments controlled common lambsquarters. Fluometuron EPOST controlled black nightshade, common lambsquarters, and common purslane ≥70, 86, and 67%, respectively. Fluometuron EPOST did not control pigweeds, velvetleaf, and common cocklebur. Cotton treated with pyrithiobac, regardless of method of application, yielded similar to the weed-free control. Cotton treated with pyrithiobac PPI at the highest rate (0.136 kg/ ha) yielded less at Halkidona, although adverse effects after its application were not visually apparent. Yield of cotton treated with herbicides was similar, with no difference among treatments.

Greenhouse and field studies were conducted to evaluate potential interactions between glyphosate and trifloxysulfuron on barnyardgrass, browntop millet, hemp sesbania, seedling johnsongrass, pitted morningglory, prickly sida, sicklepod, and velvetleaf control as well as cotton injury and yield. In the greenhouse, glyphosate at 840 g ae/ha controlled all weed species 62 to 99%, which was better than trifloxysulfuron at 2.5 or 5 g ai/ha. Control of four-leaf pitted morningglory and hemp sesbania was 80 to 88% when glyphosate and trifloxysulfuron were mixed compared with 62 to 66% control with glyphosate alone. Mixing trifloxysulfuron with glyphosate did not affect control of other species compared with glyphosate alone. In the field, glyphosate controlled barnyardgrass, prickly sida, sicklepod, seedling johnsongrass, and velvetleaf 68 to 100%. Trifloxysulfuron controlled hemp sesbania, seedling johnsongrass, and sicklepod 65 to 88%. All other species were controlled 36 to 72% with glyphosate and 10 to 60% with trifloxysulfuron. Combinations of glyphosate (840 g/ha) and trifloxysulfuron (5 g/ha) were applied postemergence over-the-top and postemergence-directed to three-, six-, and nine-leaf glyphosate-resistant cotton in the field. Cotton injury at 2 wk after treatment (WAT) was less than 13% for all herbicide treatments and less than 5% by 3 WAT. Herbicides did not affect the percent of open bolls or nodes per plant. Seed cotton yield ranged from 1,430 to 1,660 kg/ha, and only the sequential over-the-top applications of trifloxysulfuron reduced cotton yield compared with the weed-free, nontreated cotton.

Experiments examining burcucumber management in glufosinate-resistant (GR) and imidazolinone-resistant (IMI) corn were conducted in 1997 and 1998 in southeastern Pennsylvania. GR corn was planted in 38- and 76-cm rows, and postemergence (POST) treatments of glufosinate and glufosinate plus atrazine were applied to corn at the V4 or V5 growth stage. In a second study, IMI corn was planted in 76-cm rows, and 15 preemergence (PRE) and POST herbicide programs were evaluated. Herbicide treatments included RPA-201772, CGA 152005, simazine, imazethapyr plus imazapyr, imazamox, chlorimuron plus thifensulfuron, nicosulfuron plus rimsulfuron plus atrazine, CGA 152005 plus primisulfuron, and combinations with atrazine. Burcucumber germinated throughout the growing season, with greatest emergence occurring in early June, gradually decreasing to minimal emergence by mid-July. Glufosinate alone controlled burcucumber 79 to 90% 7 weeks after planting (WAP) regardless of application timing or row spacing. By 10 to 13 WAP, control was 82% or less due to lack of residual control and new burcucumber emergence. Row spacing had little effect on burcucumber emergence or control and appears to have little impact on burcucumber management in corn. In general, PRE herbicide programs were less effective than POST programs, although PRE treatments containing atrazine equaled some POST herbicides. POST-applied chlorimuron plus thifensulfuron, nicosulfuron plus rimsulfuron plus atrazine, and CGA 152005 plus primisulfuron controlled burcucumber greater than 80 and 90% in 1997 and 1998, respectively. Imazethapyr plus imazapyr and imazamox applied POST controlled burcucumber 66% 10 WAP. Adding atrazine to POST herbicide programs did not increase control, with the exception of imazethapyr plus imazapyr.

Few herbicides are used in carrot production in the United States, and none suppress volunteer potato, a serious weed where the two crops are grown in rotation. Hand-weeding is the primary method of controlling emerged volunteer potato within carrot. The objective of this work was to evaluate carrot tolerance and volunteer potato control with single or sequential applications of prometryn, prometryn plus fluroxypyr, and ethofumesate. The treatment with fluroxypyr resulted in malformed carrots with numerous root hairs and reduced carrot yield. Treatments with prometryn, either as single or sequential POST applications at 2.23 kg ai/ha, were safe on carrot and frequently controlled volunteer potato similar to the hand-weeded treatment. Ethofumesate applied as single or sequential PRE or POST at 2.2 kg ai/ha proved safe on carrot, but higher rates reduced yield. Ethofumesate applied POST or PRE followed by POST consistently reduced volunteer potato tuber mass. If registered for use in carrot, prometryn and ethofumesate would help modernize weed management in carrot and reduce or eliminate the need for hand-weeding volunteer potato.