ABSTRACT

EXPERIMENT 1. A field experiment was conducted in 1992 at Plains GA, to evaluate various Buctril herbicide systems for weed control in transgenic cotton. Weed species evaluated included a complex of Ipomoea morningglory species including ivyleaf (Ipomoea hederacea), tall morningglory (Ipomoea purpurea), pitted morningglory (Ipomoea lacunosa), ivyleaf morningglory (Ipomoea hederacea), and smallflower (Jacpuemontia tomnifolia) morningglory, sicklepod (Cassia obtusifolia), and wild poinsettia (Euphorbia hetemphylla). All herbicide rates are expressed as lb ai/ac. Buctril was applied at 1.5 lb/ac on a 9 inch band on 36 inch row cotton which corresponds to 0.375 lb/ac broadcast. All systems were cultivated within 2 days of POST or post-directed (PDS) application. All PDS applications were applied with a nonionic surfactant at 0.25% (v\v).

Herbicide systems evaluated included PPI+PRE options which included 1) no soil herbicide application, 2) Treflan at 0.75 lb/ac PPI, and 3) Treflan PPI plus Cotoran at 2.0 lb/ac PRE. These PPI+PRE options were in a factorial arrangement with five POST or PDS options which included 1) no POST or PDS application, 2) Buctril EPOST, 3) Probe at 0.75 lb/ac + MSMA at 2.0 lb/ac PDS, 4) Buctril EPOST followed by (fb) Buctril POST, 5) Buctril EPOST fb Probe + MSMA PDS, and 6) Probe + MSMA PDS fb Bladex + MSMA LPDS.

Buctril controlled wild poinsettia, smallflower morningglory, and the Ipomoea morningglories completely when evaluated soon after herbicide application. There was no difference in Ipomea morningglory control with Buctril. Control at 30 days after treatment (DAI) was still greater than 80% for the aforementioned species. Sicklepod control was unacceptable with Buctril POST. Cotoran PRE controlled wild poinsettia 70 %, smallflower morningglory 100 %, the Ipomoea momingglories 99 %, and sicklepod 98 %. The addition of Buctril improved wild poinsettia control to 98%.

EXPERIMENT 2. Buctril and MSMA were evaluated alone and in tank mixture for weed control in 1991 at Attapulgus and 1992 at Plains and also for transgenic cotton response in 1992. Buctril was applied at 0, 0.25, 0.5, 1.0, and 1.5 lb/ac in a factorial arrangement with MSMA at rates of 0, 0.25, 0.375, 0.5, and 0.75 lb/ac for a total of 25 treatments. No spray adjuvants were used with any treatment.

Buctril at 0.25 lb/ac controlled Florida beggarweed (Desmodium m 67%, sicklepod 11%, prickly sida (Sida spinosa) 87 %, and smallflower morningglory 100%. At 0.5 lb/ac Buctril completely controlled all weeds except sicklepod (17%). Buctril at the highest rate (1.5 lb/ac) controlled sicklepod 37%. No injury was observed with Buctril on transgenic cotton. MSMA alone at 0.75 lb/ac controlled sicklepod 50%, Florida beggarweed 100%, prickly sida 58%, and smallflower morningglory 49%. MSMA injury to transgenic cotton was less than 10% at 12 DAT. The addition of MSMA at 0.375 to Buctril at 0.5 lb/ac or greater generally improved sicklepod control to 80%. No antagonism was observed with the tank mixture on other weed species. Crop injury with tank mixtures of Buctril + MSMA never exceeded 9%.

Buctril will provide southeastern cotton growers with a valuable POST tool in the event of unacceptable weed control with soil-applied management systems. Buctril controls most troublesome annual broadleaf weeds in cotton with the exception of sicklepod. Buctril will suppress sicklepod growth and provide a height differential for later PDS herbicide applications. Buctril will allow cotton producers to use an IPM approach for annual broadleaf weed control in many instances.