Girdling of the main stem by the 3-cornered alfalfa hopper,Spissistilus festinus(Say), predisposed seedling soybeans to infection bySclerotium rolfsiiSaccardo, the causal agent of sclerotial blight. Growth stage V-1 was more susceptible to infection than stage V-3. The most important factor was the presence of a high inoculum level in the soil. Direct transmission by the insect was of little importance, and even simulated girdling damage resulted in infection of seedling plants.