INTERACTION OF PARAQUAT-BASED WEED-CONTROL WITH CHLOROTHALONIL-BASED DISEASE-CONTROL IN PEANUT

Understanding how weed and disease management strategies may be implem ented in combination is important for improving pest management strate gies in peanut (Arachis hypogaea L.) production. In greenhouse and fie ld studies, tank mixtures of paraquat and other herbicides, with the f ungicide chlorothalonil (tetrachloroisophthalonitrile), were evaluated for their effect on weed control and peanut injury, defoliation due t o leafspot diseases (Cercospora arachidicola and Cercosporidium person atum), and yield of peanut. In the greenhouse studies, the bipyridyliu m herbicide, paraquat, was tank-mixed with each of two formulations of the substituted aromatic fungicidal compound, chlorothalonil. Tank mi xtures consisted of 0, 0.06, and 0.12 Ib a.i./acre paraquat and each o f two chlorothalonil formulations (a liquid and a dry-flowable) at 0, 0.38, 0.75, and 1.12 Ib a.i./acre. Control of smallflower morningglory [Jacquemontia tamnifolia (L.) Griseb.] increased with increasing rate of paraquat application but was not affected with chlorothalonil in t he tank mix. Control of Florida beggarweed [Desmodium tortuosum (Sw.) DC.] and injury on peanut increased with increasing rates of both pest icides, especially with paraquat at 0.06 Ib/acre. In 2 yr of field stu dies, peanut injury due to paraquat, paraquat plus bentazon, paraquat plus bentazon plus 2,4-DB, 2,4-DB, or bentazon was not affected by the addition of chlorothalonil to tank mixtures. Three years of held stud ies on peanut show that end-of-season defoliation and yield, after a s eason-long schedule of chlorothalonil applications, were not affected when the initial fungicide application was tank-mixed with paraquat-ba sed herbicide systems or 2,4-DB alone, regardless of chlorothalonil fo rmulation. These data suggest that tank mixtures of chlorothalonil and early-season herbicides are compatible for use on peanut.