There have been very few calls or questions related to seed decay and/or seedling blights in corn. After the recent period of below normal air and soil temperatures this may change. When scouting corn fields be sure to carefully dig up stunted or yellowed plants to check roots for symptoms of seedling blights (see the April 28, 2006 issue of Integrated Pest and Crop Management Newsletter) for descriptions of the various corn seed decay and seedling blights.

Based on mild winter temperatures during December, January and February, the potential for corn flea beetle in most regions of Missouri was high for this season. The cooler than normal temperatures over the last few weeks may have slowed their activity. However, with the return to warmer temperatures there may be more flea beetle activity and more evidence of Stewart’s bacterial wilt.

On young corn plants the symptoms of Stewart’s bacterial wilt include linear, pale green to yellow streaks that tend to follow the veins of leaves and originate from feeding marks of the corn flea beetle. Lesions may extend the length of the leaf. Plants may appear stunted or somewhat distorted. If the bacteria become systemic within the plant, the entire plant wilts and may die prematurely. Cavities of a brown, soft rot can develop in the stalk pith.

Anthracnose leaf blight on young, lower leaf.

On field corn the disease tends to be limited to the leaf blight phase of the disease in which foliage symptoms develop but the pathogen does not become systemic within the plant. With the leaf blight phase of Stewart’s bacterial wilt, the linear, pale green to yellow lesions develop on the leaves. These lesions tend to parallel the leaf veins and to have wavy, irregular margins. These streaks soon become dry and brown.

The bacterium which causes Stewart’s bacterial wilt overwinters in the guts of some species of adult corn flea beetles. Adult beetles feeding on corn seedlings in late spring and early summer can contaminate the feeding wounds with the causal bacterium. Flea beetles can continue to spread the bacterium throughout the season by feeding on infected plants and then healthy plants. The potential for Stewart’s bacterial wilt to develop on young corn plants is greater after mild winters when higher levels of the corn flea beetle may be present.

Anthracnose leaf blight on upper leaf.

Most field corn hybrids have enough resistance to Stewart’s bacterial wilt that additional management is not necessary.

Anthracnose is the other foliage disease that may be evident on young corn plants early in the season. Anthracnose lesions tend to be brown, spindle-shaped lesions with yellow to reddish-brown borders. Concentric circles or zones are sometimes apparent within the diseased areas. The fungus which causes anthracnose leaf blight early in the season also causes anthracnose stalk rot late in the season. Stalk symptoms appear as black linear streaks on the surface of lower internodes on corn plants late in the season.

Laura Sweets
573-884-7307