Development and Suppression of Aerial Stem Rot in Commercial Potato Fields

The development of aerial stem rot of potato was quantified in relation to soil type, previous crop, and atmospheric temperature in the Columbia Basin. Incidence of bacterial stem rot was assessed for several weeks beginning before row closure in 18 commercial potato fields and once at the estimated peak of disease development in 38 fields over 4 years. Aerial stem rot was first observed between 25 to 36 days following row closure for 78% of the fields assessed multiple times per season. Slopes of disease progress curves initially increased very rapidly. The partial slope estimate for mean daily maximum temperature indicated an increase of disease with an increase of mean daily maximum temperature (P < 0.0001). Estimates of partial slopes for soil type (sandy loam versus silt loam) and previous crop (sweet or field corn versus other) were significant at P < 0.001 and P = 0.046, respectively, suggesting that cultivation of potato in sandy loam-type soils or following sweet or field corn as a previous crop increases the probability of aerial stem rot. Incidence of bacterial stem rot was significantly reduced in the sections of fields treated with famoxadone plus mancozeb and famoxadone plus mancozeb plus copper hydroxide mixtures.