Physoderma brown spot
Andrew Penney, Iowa State University PhD student in Plant Pathology, discusses the disease Physoderma brown spot.
Andrew Penney, Iowa State University PhD student in Plant Pathology, discusses the disease Physoderma brown spot.
Strong storms rolled across the state again bringing more heavy rain and even some damaging wind to areas. Despite the flooding in some areas and drought in the southern part of the state, 78% of the corn crop and 76% of the soybean crop was rated in the good to excellent condition based on Monday’s USDA Crop Progress Report. Iowa State University Extension and Outreach field agronomists share what they are seeing in fields across the state.
With most corn in Iowa at the V7-V12 range, it’s important to be aware of potential corn diseases at this particular time. Given the wet growing conditions over the last month, corn in parts of Iowa will be very susceptible to Physoderma brown spot and node rot, caused by the fungus Physoderma maydis, and gray leaf spot, caused by the fungus Cercospora zeae-maydis.
This past week I have been busy with disease diagnostic workshops at the ISU Field Education and Extension Laboratory. For those of you who have attended my sessions before, you know that I usually have a quiz that consists of leaves with various diseases and disease look-a-likes or imposters. I thought I’d try and write a series of blogs pointing out differences between a disease and it’s imposters.
Reports of Physoderma brown spot and stalk rot have been received from across Iowa. This disease has been increasing in prevalence across Iowa over the past decade. The disease may be confused with other common diseases. This article briefly describes the symptoms and biology of the disease.
By Alison Robertson, Department of Plant Pathology
Over the past week I have received emails, phone calls and samples of two leaf spots that occur in Iowa from time to time, Holcus leaf spot and Physoderma brown spot.
HOLCUS LEAF SPOT
Holcus leaf spot is caused by the bacterium Pseudomonas syringae. Symptoms are light tan (sometimes almost white), round to oval spots, which may appear water soaked at the margins or have a light brown border occur on the lower leaves (Figure 1 and 2).