In the past week, the Iowa State University Plant Disease Clinic has received corn leaf samples from northwest Iowa with Holcus leaf spot. Holcus leaf spot is caused by the bacterium Pseudomonas syringae. Light tan (sometimes almost white), round, oval spots, which may appear water soaked at the margins or have a light brown border occur on the lower leaves. The spots are initially about 1/4 inch in diameter, but sometimes grow larger and coalesce into irregular spots and streaks of dead tissue.