ABSTRACT

Research evaluated Buctril systems at Plains, Georgia in 1991 and 1992, and Buctril + Cotoran postemergence (POST) tank mixtures at Tifton in 1991 and Plains in 1992 for weed control efficacy in transgenic cotton. Weed species evaluated included coffee senna (Cassea occidentalis), Ipomoea morningglories, wild poinsettia (Eiphorbia heteropylla), prickly sida (Sida spinosa), sicklepod (Cassia obtusifolia), smallflower morningglory (Jacquemontia tamnifolia), and yellow nutsedge (Cyperus esculentus). All plots in each experiment received Treflan preplant incorporated at 0.75 lb ai/ac. Transgenic cotton yields were not taken due to Environmental Protection Agency regulations. A nonionic surfactant at 0.25 % (v/v) was used with all post directed (PDS) treatments but was not used with Buctril POST. Buctril systems Premergence treatment options were either 1) none, or 2) Cotoran at 1.0 lb ai/ac. POST system options were 1) Buctril 1.5 lb ai/ac at 2-6", 2) Buctril at 2-6" followed by (fb) Buctril at 6-10", 3) Buctril at 2-6" fb an early post- directed (EPDS) treatment of MSMA at 2.0 lb ai/ac + Probe at 0.75 lb ai/ac. 4) MSMA + Probe EPDS fb a late post-directed (LPDS) treatment of MSMA + Bladex at 0.80 lb ai/ac. Buctril application was made according to cotton height. PRE and POST treatment options were in a factorial arrangement.

All systems provided $99% Ipomoea morningglories, $99 smallflower morningglory, and $91 % wild poinsettia control. POST systems with Buctril provided $92% coffee senna and $99% prickly sidar control. MSMA + Probe EPDS fb MSMA + Bladex LPDS gave the best sicklepod and yellow nutsedge control. Cotoran PRE fb sequential POST Buctril treatments, Buctril fb EPDS or EPDS fb LPDS gave 82, 92, and 95 % sicklepod control, respectively. POST systems with Buctril and without Cotoran PRE gave #59% sicklepod control. Cotoran PRE gave 100% smallflower morningglories, 100% smallflower morningglory, and 91% wild poinsettia control, but only 67 and 63% coffee senna and prickly sida control, respectively.

Buctril + Cotoran tank mixtures

Buctril rates were none, 0.38, 0.50, 0.75, 1.0, and 1.5 lb ai/ac in a factorial arrangement with Cotoran at none, 0.25, 0.50, and 0.75 lb ai/ac. All Cotoran or Cotoran tank mixtures were applied with a nonionic surfactant at 0.25 % (v/v) of the spray volume.

Buctril at 0.38 lb/ac and higher provided $92% Ipomoea morningglories, $96% smallflower morningglory, and 100% wild poinsettia control. Buctril at 1.5 lb/ac and Cotoran at 0. 75 lb/ac gave only 55 and 38 % sicklepod control, respectively. Buctril at 1.5 + Cotoran at 0.75 lb/ac gave the best (81%) sicklepod control. Cotoran at 0.75 lb/ac gave excellent (98%) Ipomocea morningglories and (93%) smallflower morningglory control, but only 72% wild poinsettia control.

There was no crop injury from Buctril applied alone. Crop injury from Cotoran at 0.25, 0.50, and 0. 75 lb/ac was 19, 16, and 16 %, respectively. Crop injury was minimal and variable, but increased with increasing Buctril and Cotoran tank mixture rates from 8 to 30% at 4 days after treatment (DAT). However, Cotoran alone at 0.25, 0.50 and 0.75 lb/ac and in tank mixture with Buctril resulted in crop injury of # 15% by 14 DAT.