Studies were conducted in 1991, 1992 and 1993 to evaluate nightshade efficacy and Acala cotton phytotoxicity of the over the top selective broadleaf herbicide phrithiobace (Staple). Rates of 0.5, 0.75, 1.00, 1.50, 2.0 and 3.0 oz ai/a as well as tank mix applications with fluazifop (Fusilade), and monosodium methanearsonate (MSMA) with non-ionic and crop oil surfactants were evaluated.

Nightshade control has been excellent. Control levels 50 to 60 days after treatment have ranged from 90 to 100 percent, with 100 percent control normally occurring at the 1.0 to 1.5 oz ai/a rate applied either singly or in a sequential application. When phrithiobace was tank mixed with either fluazifop or monosodium methanearsonate control remained excellent. Grass control was also unaffected as was nutsedge control.

Cotton injury symptoms are evident, as with weeds, 4 to 5 days after treatment. Symptoms include mottled yellowing and crinkling of leaves, but the cotton plant soon outgrows these symptoms within 30 to 40 days. Symptoms are greater and persist longer with higher rates. Acala varietal screening indicated no adverse effect to yield.