Current Status of Soybean Stem Canker in Florida

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Abstract
Soybean-growing areas in Florida were surveyed in 1983, 1984, and 1985 for soybean stem canker [Diaporthe phaseolorum]. Incidence of the disease was much lower in 1984 and 1985 than in 1983. As many as 81% of the fields in a given county in 1983 contained diseased plants, but the highest comparable proportions in 1984 and 1985 were 8 and 2%, respectively. An abrupt reduction in the use of susceptible cultivars was observed during the 1984 and 1985 seasons in counties where the disease was perceived as a threat to soybean production after 1983 (counties with severe stem canker in 1983 or in adjacent counties). Whereas about 50% of the seed sold in these counties in 1983 were susceptible to stem canker, generally less than 10% of the seed sold in the same counties in 1984 and 1985 were of susceptible cultivars. In contrast, in counties not affected by stem canker in 1983 about 50% of the seed sold during 1984 and 1985 were of susceptible cultivars.