CONTROL OF RHIZOCTONIA-SOLANI DAMPING-OFF IN COTTON BY SEED TREATMENT WITH FUNGICIDES

Rhizoctonia solani, which frequently induces seedling diseases in cotton fields in Israel, was isolated from diseased seedlings and from soils where cotton was grown. There was a positive correlation between isolation of R. solani from diseased seedlings and reduction in field stands. Occasionally, Rhizoctonia bataticola (Macrophomina phaseolina) also was isolated from diseased seedlings. The cultivar (cv.) Acala SJ-2 shows more resistance to R. solani damping-off than does cv. Pima. Under laboratory conditions, seed treatment with fungicide combinations such as quintozene plus etridiazole, tolclofos-methyl plus thiram, pencycuron plus captan, carboxin plus thiram, carboxin plus captan, quintozene plus captan, and thiabendazole plus thiram significantly increased the percentage of seedling emergence and decreased the disease index in cotton seedlings. In several cases, a mixture of thiabendazole plus hydroxyquinoline in glycolic acid and oxine-copper also decreased disease incidence. These results were obtained with both cv. Acala SJ-2 and cv. Pima S-5, growing in either naturally or artificially infested soils. Caspan (ethoxy mercuric chloride), the only fungicide currently in use for seed treatments, had no effect, which may explain why there is a high incidence of seedling disease in some cotton fields in Israel. All the above-mentioned fungicides were highly effective for the control of seed-borne Rhizopus spp.