Weed Efficacy with Buctril and Roundup

John S. Richburg, III, John W. Wilcut, and E. G. Ingram


Experiments conducted in 1992 and 1993 in Tifton, Georgia evaluated Buctril rates and application timings for broadleaf weed efficacy. Buctril rates evaluated were 0.25, 0.38, 0.50, 0.75, 1.0, and 1.5 lb ai/acre. Buctril does not require a surfactant. Three separate application timing experiments were conducted with these six Buctril rates, plus a nontreated check for comparison. The target application timings were 1-3, 3-4, or 5-6 inch weeds. However, the size of weeds at the time of application were recorded since there were larger or smaller weeds in some instances. Weed species were planted in strips across each rep. Weed species evaluated included cocklebur (Xanthium strumarium), coffee senna (Cassia occidentalis), Ipomoea morningglory spp., Florida beggarweed (Desmodium tortuosum), Florida pusley (Richardia scabra), hemp sesbania, (Sesbania exaltata), jimsonweed (Datura stramonium), pigweed spp. (Amaranthus spp.), prickly sida (Sida spinosa), sicklepod (Cassia obtusifolia), smallflower morningglory (Jacquemontia tamnifolia), wild poinsettia (Euphorbia heterophylla), wild radish (Raphanus raphanistrum), and velvetleaf (Abutilon theophrasti). Visual ratings were taken 7 days after treatment.

Buctril at 0.25 lb/ac applied to < 4 inch tall weeds provided at least 95% control of all weeds evaluated except for pigweed spp. and sicklepod. Buctril at 0.75 lb/ac was required for comparable control of all weeds > 5 inches except for pigweed spp. and sicklepod. Buctril at 0.75 lb/ac controlled 1-3 inch pigweed spp. 90%, 1.00 lb/ac was required for 90% control of 3-4 inch pigweed, and 1.5 lb/ac gave 81% control of 6-7 inch pigweed spp. Buctril at 1.5 lb/ac provided only 60% control of sicklepod < 4 inches tall and only 44% control of sicklepod 4-8 inches tall. Buctril provides excellent postemergence control of many annual broadleaf weeds in Georgia cotton. Buctril does not control sicklepod, but will help provide a height differential for post-directed applications.

Separate experiments were conducted to evaluate Roundup rates on broadleaf and grass weed efficacy in 1993 in Tifton, Georgia. Weed seed were scattered over each plot and incorporated in 2 inches. Roundup rates evaluated were 0.25, 0.50, 0.75 and 1.00 lb ai/acre. A nontreated check was included for comparison. A nonionic surfactant at 0.25% v/v was included with all Roundup treatments. Broadleaf weed species evaluated included common cocklebur, Florida beggarweed, Ipomoea morningglory, smallflower morningglory, and sicklepod. Grass species evaluated included large crabgrass (Digitaria sanguinalis), crowfootgrass (Dactyloctenium aegyptium), seedling johnsongrass (Sorghum halepense), and Texas panicum (Panicum texanum). Grass species were under severe moisture stress at the time of application. Visual ratings were taken 14 days after treatment.

Roundup at 0.50 lb/ac provided > 90% control of seedling johnsongrass and Texas panicum, but 0.75 lb/ac was required for at least 80% control of large crabgrass and crowfootgrass. Roundup at 0.25 lb/ac provided > 95% control of smallflower morningglory and cocklebur and 100% Ipomoea morningglory control with 0.50 lb/ac. Roundup at 0.75 lb/ac provided > 85% control of Florida beggarweed and sicklepod. Sicklepod control with Roundup is moisture sensitive. Dry soil moisture conditions at application of Roundup may require 0.75 lb/ac for sicklepod control. Good soil moisture with actively growing sicklepod plants are more susceptible to Roundup.

Buctril resistant and Roundup resistant cotton varieties have been developed, but are not currently available. It must be noted that Buctril and Roundup will kill normal cotton. Buctril and Roundup herbicides will provide a much needed tool for over-the-top weed control of numerous weeds in Georgia cotton.

Reprinted from Proceedings of the 1994 Beltwide Cotton Conferences pg. 1702
©National Cotton Council, Memphis TN

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Document last modified Sunday, Dec 6 1998