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Perennial Weed Control in Roundup Ready™ Cotton

J.M. Chandler, E.P. Prostko, L.D. Bradshaw


In Central Texas both annual and perennial morningglory species infest most cotton fields. The predominant annual species include pitted morningglory, entireleaf morningglory and ivyleaf morningglory. Sharppod morningglory is the predominant perennial species and accounts for approximately 60% of the morningglory population. Johnsongrass with its perennial growth habit still ranks among the most common and troublesome weeds infesting cotton. The adoption of conservation tillage systems for the production of cotton in Texas will greatly aid in the persistence of perennial weed species such as sharppod morningglory and johnsongrass. In 1995 field experiments were conducted in the Brazos bottom near College Station, Texas to determine the level of perennial sharppod morningglory and johnsongrass control with Roundup in Roundup Ready cotton. The sites were disked, chisel-plowed and bedded in October, 1994. The sharppod morningglory study was conducted on a Roetex clay soil as a factorial in a randomized block design with four replications. Conventional cropping techniques were used through the production season. The sharppod morningglory population was a natural infestation of perennial and annual plants. Treflan at 0.75 lb ai/A was broadcast on the beds and incorporated with a rolling cultivar 19 days prior to planting. At planting Caparol at 1.0 lb ai/A was applied. Roundup at 0.56, 0.75 and 1.12 lb ae/A was applied broadcast over-the-top when the cotton was in the 2 true leaf (2L) and 4 true leaf (4L) stages. The sharppod morningglories had four inch runners with ten leaves per plant. Additional postemergence directed (PDR) applications of Roundup at 0.56 lb ae/A were made in cotton with 9 (PDR9) or 11 (PDR11) true leaves. The morningglories were mainly seedlings with 4 to 6 true leaves. The johnsongrass study was conducted in a split-plot design with four replications on a Burco clay. Main plots were Prowl at 0.75 lb ai/A applied broadcast to the beds and incorporated with a rolling cultivator on February 24. The beds were rolled and a stale seed bed system established. The sub-plots included nine control systems using Roundup and/or Gramoxone applied at various crop growth stages. At planting, seedling and rhizome johnsongrass ranged in height from 1 to 24 inches. A preemergence broadcast application of Caparol at 1.0 lb ai/A was made into the existing vegetation. Roundup at 0.56 or 0.75 lb ae/A and Gramoxone at 0.625 lb ai/A were applied broadcast over-the-top at planting (PLNT) to selected control systems. Additional broadcast over-the-top applications of Roundup at 0.37 and 0.56 lb ae/A were applied when the cotton was in the 4 to 5 true leaf (4-5L) stage. Depending on prior treatments, johnsongrass stages ranged from 2 inch seedlings to rhizome plants 29 inches tall and in the boot stage. Additional postemergence directed applications of Roundup at 0.56 lb ae/A were made in cotton with 7 (PDR7) or 13 (PDR13) true leaves. The johnsongrass was mainly seedlings 4 to 5 inches tall.

Reprinted from Proceedings of the 1996 Beltwide Cotton Conferences pp. 1529 - 1530
©National Cotton Council, Memphis TN

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Document last modified Sunday, Dec 6 1998