P. A. Dotray, T. A. Murphree, G. G. Light, W. J. Grichar, J. W. Keeling, T. A. Baughman, and V. B. Langston. Texas Tech University, Lubbock; Texas Agricultural Experiment Station, Lubbock and Yoakum; and Texas Cooperative Extension, Vernon; and Dow AgroSciences, The Woodlands, TX.
Peanuts continue to be an important crop for producers in Texas, although the acres harvested in 2002 (280,000) declined compared to acres harvested in 2001 (310,000). Average peanut yields, which increased from 2890 lb/A to 3100 lb/A, were in part the result of improved weed control. Since 2000, new soil-applied herbicides have been used to improve annual broadleaf weed control in peanuts. During its 2000 launch year, diclosulam slowed peanut emergence, caused stunting, discoloration, and stand loss on the Texas High Plains. Since the 2000 growing season, label restrictions prohibit the use of diclosulam on soils with a pH of 7.2 or greater, which is essentially all soils in the Texas High Plains peanut region. Experiments on soil type, watering frequency, and peanut variety have been conducted to better understand the cause of this injury. The objective of this experiment was to examine the efficacy and peanut tolerance following diclosulam applied postemergence. Twenty large plot field experiments were established on the Texas Southern High Plains in 2001. Additional experiments in 2001 and 2002 were conducted at Flomot and Lelia Lake (Rolling Plains), Lamesa (Southern High Plains), and Yoakum (South Central Texas). In the large plot studies, diclosulam was applied at 0.008 lb ai/A, , 0.016 lb ai/A, 0.016 lb ai/A + 2,4-DB (0.25 lb ai/A), and 0.024 lb ai/A and comparisons were made to the grower standard. In the additional small plot experiments, diclosulam was applied alone (0.004, 0.008, 0.012, 0.016, 0.024, 0.031, and 0.048 lb ai/A) and in combination with 2,4-DB (0.025 lb ai/A) plus crop oil or bentazon (1.0 lb ai/A) plus crop oil. Peanut injury from diclosulam applied postemergence was observed at 2 of 20 locations (up to 10%). A transient yellow chlorosis was observed that lasted approximately 8 days. Typical 2,4-DB injury was observed at several of these locations. Five of the 20 locations were harvested, and no adverse affects on yield were observed. Diclosulam postemergence had activity on many common weeds in Texas peanut. Diclosulam at 0.016 lb ai/A control devil’s-claw 99% (averaged over 10 locations), common cocklebur 95% (1 location), golden crownbeard 99% (6 locations), Palmer amaranth 78% (5 locations), Russian thistle 78% (7 locations, yellow nutsedge 87% (3 locations), purple nutsedge 90% (1 location), and annual morningglories 77% (3 locations). In the small plot studies, no visual injury was observed throughout the growing season following diclosulam applied postemergence; however, diclosulam applied preemergence injury peanut nearly 50% and at-crack injured peanut nearly 10% early season . Diclosulam at 0.016 lb ai/A controlled purple nutsedge and ivyleaf morningglory at least 80% at Lamesa. At Flomot, diclosulam at 0.016 lb ai/A plus crop oil controlled ivyleaf morningglory and Palmer amaranth at least 80% on August 7, but yellow nutsedge control from this treatment at Lelia Lake was unsuccessful (less than 30%). These studies suggest that diclosulam postemergence has good activity on several weeds in Texas peanut, but the future of this application timing remains uncertain.