ABSTRACT

Dual (metolachlor) herbicide is a residual herbicide which controls many annual grasses and small seeded broadleaf weeds. It also has activity on yellow nutsedge (Cyperus esculentus). Dual is currently registered for use in corn, peanuts, and soybeans, and in cotton, its registration and use are limited primarily to states in the Mid-South and Southwest. Concerns about potential cotton injury have restricted expansion of its uses in the Southeast. Although Dual does not effectively control Texas panicum (Panicum texanum), the most common and troublesome annual grass in Georgia, it does offer potential for suppression or control of yellow nutsedge.

Over the past two seasons, nine experiments were conducted to evaluate weed control and cotton injury with Dual in the sandy soils of Georgia. Yellow nutsedge control was a primary weed in most of these studies. Rates below 1.0 lb. AI/A did not provide adequate nutsedge control. With preemergence applications, nutsedge control at 2.0 lb. Al/A aver-aged 78 percent. Improved nutsedge control was observed with Dual (1) preceded by a preplant foliar application of Roundup (glyphosate), (2) added with Gramoxone (paraquat) at planting, or (3) followed by postemergence applications of Staple (DPXPE350). Crop injury with preemergence applications of Dual ranged from 0 to 93 percent. Variability in weed and crop response were dependent primarily on rainfall and irrigation. In a comparison of preplant incorporated and preemergence treatments of Dual at two rates, cotton injury was similar and ranged from 26 to 37 percent. Potential for cotton injury should preclude the routine use of Dual as a preplant or preemergence treatment in the coarse textured, low organic matter soils of Georgia.

In limited observations, early postemergence (over-the-top) applications of Dual provided fair to good nutsedge control. Activity was probably enhanced by irrigation and frequent rainfall. Over-the-top treatments were less injurious to cotton than preemergence treatments. Addition of Dual with postemergence directed applications of MSMA improved nutsedge control compared to MSMA alone. Layby applications also showed promise.