Resistance is effective in both the seedling and the mature plant. Aphanomyces Seedling Disease and Root Rot of Sugarbeet. As with Phytophthora, recent soil temperatures have been too cool for optimum infection, but a couple of warm sunny days could change that. Infection in the seedling stage may result in seedling death or unthrifty seedlings with black root tips. Later infection may result in plants that are greenish-yellow and wilt at midday.
Infected plants have very little tap root.
Some varieties are tolerant to Aphanomyces, but none is highly resistant. Seed pelleting with Tachigaren should be used in conjunction with use of a tolerant variety when planting into a field known to have Aphanomyces. Indexing of fields for Aphanomyces potential is available through sugar cooperative agriculturists. Sugarbeet Rhizomania , caused by the beet necrotic yellow vein virus, is transmitted by a soil borne water mold, Polymyxa betae. The fungus is active in wet soils when the soil temperature is at least 60F, with an optimum at 77F. Symptoms.