In the past week, I have viewed several corn fields around the Vassar, MI, area which are believed to be infested with Holcus leaf spot.

I’ve also submitted leaf samples to the MSU plant diagnostic lab for confirmation.

Holcus leaf spot is caused by the bacterium Pseudomonas syringae. Its host range is extremely broad and includes grasses such as foxtail millet, pearl millet, Sudan grass, Johnson grass, wheat and sorghum.

The spots are round, oval spots that may appear light tan in color. They spots may also appear water soaked at the margins or have a light brown border occurring on the leaves. Spots are initially about 1/4 inch in diameter, but are sometimes larger and can also appear irregular with streaks of dead tissue. The lesions later dry out, turn light brown, and have a papery texture. Many times the spots resemble chemical injury similar to paraquat drift.

Holcus leaf spot is mostly cosmetic and does not result in yield loss. These spots occur from bacteria splashed onto the leaves and invade the plants through stomates or wounds caused by hail, blowing soil or wind. The infestation often results following warm (77-86 degree F.), rainy weather early in the season.

When the disease is a problem, crop rotation and tillage of debris are often recommended for control, although they are not very effective because of the broad host range of the bacterium.

TEX

Tex Young, CCA
Sales Agronomist
Great Lakes Hybrids