Effect of a select group of seed protectant fungicides on growth of Sclerotinia minor in vitro and its recovery from infested peanut seed

Potato-dextrose agar containing 100 mug of streptomycin sulfate per millili ter of medium (SPDA) was amended to establish levels of 0, 2, 4, 6, 8, and 10 mug/ml of the fungicides thiophanate-methyl, carboxin, dicloran, captan, pentachloronitrobenzene (PCNB), or thiram. Fresh mycelial plugs, dry mycel ial fragments, and sclerotia of Sclerotinia minor were placed onto the amen ded media, and mycelial growth and sclerotial germination were determined f or 7 days. Thiophanate-methyl was the most effective chemical in inhibiting growth of S. minor, followed by PCNB and dicloran. Thiophanate-methyl was the only chemical that prevented germination of sclerotia of S. minor. Pean ut seed naturally infested with S. minor was treated with the fungicides al one or in various combinations; control seed was treated with talcum powder . Seed was stored in polyethylene bags for 12 weeks at 24 degreesC. To dete rmine the incidence of viable S. minor in treated seed, seed was removed fr om bags, washed for 1 min in 0.2% unscented, liquid soap solution, rinsed t wice in distilled water, and then dried for 15 min prior to plating on SPDA . The incidence of S. minor in talcum and thiophanate-methyl treated seed w as 3.68 and 0.0%, respectively. Incidence of S. minor in seed treated with the other compounds ranged from 0.40 to 0.56%. Subsequent tests were perfor med using thiophanate-methyl and some of the above chemicals, in combinatio ns or alone. These tests confirmed that thiophanate-methyl was the only com pound that consistently reduced recovery of S. minor from infested seed. Ge rmination of thiophanate-methyl treated seed equaled that of seed treated w ith talcum.