Part 2, Section 4: Soybean Pest Management

Section 4 Table of Contents

Soybean Pest Management

DISEASES

Late-Season Diseases

Phomopsis seed decay and Purple seed stain are two common seed diseases in Pennsylvania. These diseases can result in significant reduction in grain quality and yield losses when environmental conditions favor disease development. Losses are most significant when harvest is delayed by wet weather.

Phomopsis seed decay. Symptoms of Phomopsis seed decay include seed that is shrunken, elongated, and cracked. Infected seed may become white and chalky in appearance. Affected seeds usually do not germinate or are slow to germinate. Phomopsis can also result in pre- and postemergence death of seedlings.

Purple seed stain. This disease is easily distinguished by the pronounced purple to pink discoloration of infected seed. The discoloration may occur as specks or as large irregular blotches on the surface of the seed. In some cases, the entire seed coat may be discolored. Seed with purple seed stain may have reduced germination, and seedling diseases may also result from the seed infections.

Management of Seed Diseases

The fungi that cause Phomopsis seed decay and purple seed stain survive in crop residues left on the soil surface. Producers can reduce their risk of disease by using crop rotation to limit exposure to the inoculum source. A 1- to 2-year rotation to corn or small grains should be sufficient to reduce the pathogen population in most fields. Tillage can also be used to hasten decomposition of crop residues, but these practices may have negative impacts on soil erosion.