(Written by U of I Plant Clinic Student Volunteer Zu Dienle)
We have recently received a sample of soybean seedlings infected with root rot. This root rot disease is caused by a common fungus known as Rhizoctonia solani. Watch out for symptoms such as lesions and reddish discolorations near the roots and stems. Soybean seedlings may also experience stunted or irregular growth as a result of girdling at the base of the stem. The rot on the root differs from those caused by oomycetes (Pythium or Phytophthora) in the sense that it is dry.
Rhizoctonia only causes problems if conditions are favorable and some yield losses can be observed. Commonly in Illinois, the disease makes it presence known around the early spring when weather conditions are wet. During severe conditions, R. solani can cause up to 50 percent stand losses! This disease is especially prevalent under stressful conditions – injuries, herbicide applications, nutrient imbalances are all possible precursors to root rot disease development.
In order to diagnose Rhizoctonia, we place rotted root tissue under the microscope and identify the characteristic right-angled hyphae. Some other common characteristics to look out for are segmentations in the hyphae near the branching points and constrictions near these segmentations. In certain cases, the hyphae can be pigmented.
If you find your soybean infected with R.solani, below are some management strategies that you can employ:
There is no better way to stop a problem than avoiding it at the start! Ensure that the seeds come from a disease-free, certified stock. Make sure that the seeds are all “healthy” with no visible cracks or discolorations. Certain fungicide treatments can be applied to seeds can help to control the Rhizoctonia pathogen.
When planting these seeds, make sure that the area is not a previously infected site, as R.solani can survive up to many years in the soil. Crop rotation from time-to-time to non-host is recommended. An ideal planting site is a warm (60 Fahrenheit or 15.5 Celsius and above) seedbed with proper tillage. Ensure that the other components of the soil such as its nutrient levels and pH are adequate.
For more information, visit: http://ipm.illinois.edu/diseases/series500/rpd511/index.html
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