Field Evaluations of the Herbicidal Effects of Fluridone on Two Soils

The selective control of perennial weeds in cotton (Gossypium hirsutum L.) with soil applied herbicides has been difficult to achieve with currently available chemicals. Also, the long-term use of the dinitroaniline herbicides in cotton has resulted in a shifting of the weed spectrum to species which are resistant to these herbicides. New herbicides are needed to control these weed problems. The purpose of this study was to evaluate fluridone {l-methyl-3-phenyl-5-[3-trifluoromethyl)phenyl] -4(lH)-pyridinone}, a newly developed soil applied herbicide, for effectiveness in the control of various annual and perennial weeds found in cotton. Fluridone, at several rates, was applied preplant incorporated or preemergence to Miller clay, a fine, mixed thermic vertic Haplustolls, and Lufkin fine sandy loam, a fine montmorillonitic, thermic vertic Albaqualfs, in the springs of 1976, 1977, and 1978 and in the fall of 1977. Weed control evaluations in cotton were made periodically after application. Spring applications of 0.45 kg/ha or higher effectively controlled broadleaf weeds for the growing season. Fluridone at 0.45 and 0.90 kg/ha effectively controlled rhizome johnsongrass [Sorghum halepense (L.) Pers.] 2 of 3 years evaluated. Season-long control of yellow nutsedge (Cyperus esculentus L.) in a sandy loam soil was observed with preplant incorporated and preemergence rates of 0.90 kg/ha. Phytotoxic effects of fluridone residue were noted in a sandy loam soil one year after treatment but these effects were not as evident in the clay soil. Fluridone applied in the fall provided variable weed control the following spring depending upon soil type, weed density, and weed species present. Incorporation of the fall treatments increased the effectiveness of fluridone on annual grasses in the sandy loam soil. These experiments determined that fluridone could effectively control yellow nutsedge, rhizome johnsongrass, and many annual weeds in cotton at rates above 0.45 kg/ha but the residue of this treatment may limit the use of rotational crops the following year.