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Crop disease diagnosis and plant health: The U of M Plant Disease Clinic is ready to help

Source: Dave Nicolai, Extension Educator, Crops, UMN Extension

The improvement of plant health (and yields) can only be successfully achieved after a clear understanding is made of what is reducing plant health in the first place. This is where the Plant Disease Clinic (PDC), can help. The PDC is based on the St. Paul campus at the University of Minnesota. It provides diagnostic services, specializing in microbial pathogens of plants. The PDC diagnoses thousands of samples each year from state and federal agencies, the agriculture and horticulture industry, and the general public.

For single season crops like corn and soybean, it is particularly important to pay close attention to plant health problems early in the growing season. Diseases that start in June will tend to have a much greater impact on final yields than diseases that don’t get started until much later in the summer. There are multiple pathogens and abiotic issues that can cause similar symptoms and a misdiagnosis based on an incorrect assumption can lead to expensive and wasteful treatment applications, as well as not fixing the original problem!

Accurate diagnosis also requires high quality and timely samples. Plants that are symptomatic but still living are typically the best to submit. Every fall the PDC receives soybean samples submitted by growers that suspected they had a disease issue but were simply too busy during the active growing season to submit them. In many cases the dead soybean plants are impossible to diagnose as saprophytic organisms have colonized the tissues and it is not possible to be sure which organism caused the initial disease.

Pythium root rot, Rhizoctonia root and stem rot, Fusarium root rot, and Phytophthora root rot are common soybean seedling diseases in Minnesota, which the U of MN Plant Disease Clinic can help to determine. The soilborne pathogens that cause these diseases are widespread and persistent in field soils across the state. These pathogens are also key targets for most fungicidal seed treatments.

• Pythium root rot. The wet and cool soils that occurred in many areas with the frequent rains in late May have been especially favorable for Pythium seed and seedling root rot. Pythium infections typically result in brownish-colored, rotting tissue.
• Phytophthora root rot is also favored by wet and saturated soils, although it generally prefers warmer soil conditions than Pythium root rot. The light, soft-rot symptoms on roots caused by Phytophthora are very similar to those caused by Pythium, and laboratory diagnosis may be required to tell which disease it is. Phytophthora can damage soybean seedlings or initiate infections in the spring that may result in severe root and stem rot in July and August.
• Rhizoctonia root and stem rot caused by Rhizoctonia solani is also a widespread problem in Minnesota. Warm and moist soils favor Rhizoctonia root and stem rot. Plant stand loss can be high when soil is warm (>74F) and wet while seedlings are in the VE to V1 growth stages, as these are prime conditions for disease development. Reddish to dark brown, firm and often sunken, lesions caused by Rhizoctonia develop on the stem and often girdle stems near the soil line.
• Fusarium root rot is another common soybean seedling disease in Minnesota that can cause significant damage. The typical symptoms are damping-off and root-rot with dark brown lesions.

Please consult the PDC website ( or call at 612-625- 1275 for instructions on sample submission, fees for diagnosis, and additional information.


David Nicolai
Extension Educator, Crops & Institute for Ag Prof Coord
(651) 480-7706
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