Field experiments were conducted in 1997 and 1998 near Columbia and Novelty, MO, and Urbana, IL, to evaluate crop injury, weed control, corn yield, and net economic returns provided by weed control programs in glyphosate-resistant corn. The herbicide programs evaluated included acetochlor preemergence (PRE) followed by (fb) glyphosate with or without atrazine postemergence (POST) and total POST programs consisting of single and sequential applications of glyphosate alone and tank-mixed with actochlor, atrazine, or both. Metolachlor PRE fb dicamba plus atrazine POST and metolachlor plus atrazine PRE were included for comparison. In the total POST treatments, mid-post (MPOST) applications provided better control than early-post (EPOST) applications on weeds that germinated throughout the growing season such as shattercane and common cocklebur, but also resulted in yield reductions of up to 23% caused by early-season weed competition. The addition of atrazine to glyphosate POST generally increased control of common cocklebur, morningglory species, and common waterhemp. EPOST or PRE fb EPOST applications generally provided higher yields than MPOST treatments, although MPOST treatments often provided equal or greater weed control at midseason. Treatments including two herbicide applications tended to provide greater weed control, yield, and profit than those with a single application. Input costs for glyphosate-resistant corn are slightly higher than nontransgenic hybrids. However, net economic returns are similar and the use of glyphosate POST allows greater flexibility in POST weed management decisions.

Field experiments were conducted in 1995 and 1996 at DeKalb and Urbana, IL, to evaluate weed management systems in glyphosate-resistant soybean planted in rows 76 cm wide. These experiments compared weed control using preemergence (PRE) herbicides followed by glyphosate or postemergence (POST) tank-mix combinations of glyphosate and acetolactate-synthase-inhibiting herbicides with glyphosate applied alone at 0.63 kg ae/ha in single or sequential applications. Overall, the use of a tank-mix partner or a PRE herbicide followed by glyphosate improved weed control compared to a single application of glyphosate. However, weed control with these treatments was not better than with sequential applications of glyphosate. Control of giant foxtail exceeded 90% for single applications of glyphosate except at DeKalb in 1995 when late emergence of giant foxtail occurred after POST applications had been made. A PRE grass herbicide or a late postemergence (LPOST) application of glyphosate was necessary for season-long control of late-emerging giant foxtail. Tank-mixing glyphosate with imazethapyr, cloransulammethyl, and CGA-277476 or applying glyphosate LPOST following these herbicides improved giant foxtail control compared with these herbicides applied alone. A single application of glyphosate controlled common lambsquarters 88% or greater in two of three trials. At Urbana in 1995, a single application of glyphosate controlled common lambsquarters 78% compared to 88 to 96% control with PRE herbicides followed by glyphosate or sequential applications of glyphosate. Velvetleaf control with a single application of glyphosate ranged from 55 to 78%. A PRE application of chlorimuron + metribuzin, cloransulammethyl, or sulfentrazone followed by glyphosate POST, as well as sequential applications of glyphosate, consistently improved velvetleaf control compared to a single application of glyphosate. In some cases, adding glyphosate to a POST application of imazethapyr or CGA-277476 improved control of velvetleaf but decreased velvetleaf control when added to cloransulammethyl.

Transformation of soybean [Glycine max (L.) Merr.] with a gene encoding a glyphosate‐tolerance 5‐enolpyruvylshikimate‐3‐phosphate synthase enzyme from Agrobacterium sp. strain CP4 resulted in the development of glyphosate‐tolerant line 40‐3‐2. Glyphosate (N‐phosphonomethyl glycine) is the active ingredient of Roundup herbicide. Line 40‐3‐2 was yield tested at 17 locations in 1992,23 locations in 1993, and 18 locations in 1994. At those locations, broadcast applications of glyphosate at various rates were made over 40‐3‐2 or its derivatives from early vegetative growth to pod fill. No significant yield reduction was observed as a result of the glyphosate treatment at any of the locations. Development of glyphosate‐tolerant soybean promises to provide the farmer with access to a new weed control system that should result in lower production costs and reliable weed control under a wide range of conditions.

Greenhouse and laboratory experiments were conducted to evaluate foliar absorption, translocation, and efficacy of glufosinate on four weed species. The rate of glufosinate required to reduce shoot dry weight by 50% (GR50) varied between weed species. GR50values for giant foxtail, barnyardgrass, velvetleaf, and common lambsquarters were 69, 186, 199, and 235 g ai ha−1, respectively. Absorption of14C-glufosinate increased with time and reached a plateau 24 hours after treatment (HAT). Absorption of14C-glufosinate was 67, 53, 42, and 16% for giant foxtail, barnyardgrass, velvetleaf, and common lambsquarters, respectively. Translocation of absorbed14C-glufosinate from the treated leaf was greatest for giant foxtail and barnyardgrass (15 and 14% 24 HAT of absorbed14C-glufosinate, respectively). This compared to 5 and < 1% for translocation of absorbed14C-glufosinate from the treated leaves of velvetleaf and common lambsquarters. The majority of14C-glufosinate translocated by giant foxtail and barnyardgrass was found below the treated leaf and in the roots, indicating phloem mobility of the herbicide. Differential absorption and translocation of14C-glufosinate may be contributing factors to the differential sensitivity observed between weed species.

Studies were conducted in 2002 and 2003 on a golf course fairway in New Jersey to compare spring, summer, and fall treatments of bispyribac-sodium for annual bluegrass control and creeping bentgrass tolerance. Single applications at 74, 111, or 148 g ai/ha were applied in May, August, or October. Split applications of 37 followed by (fb) 37 or 74 fb 74 g/ha applied 3 wk apart were also evaluated. Summer-applied bispyribac-sodium did not reduce bentgrass quality, whereas spring and fall treatments reduced turf quality at 3 wk after treatment and fall treatments in 2002 substantially reduced bentgrass quality. Summer treatments were more effective than spring or fall treatments in reducing annual bluegrass cover. Final evaluations revealed 36, 31, 21, and 26% annual bluegrass cover averaged across nontreated, spring-treated, summer-treated, and fall-treated plots, respectively. This study demonstrates that two split applications of bispyribac-sodium at 74 g/ha in summer can effectively reduce annual bluegrass cover while minimizing creeping bentgrass injury.