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Phytophthora damping off and root rot are destructive diseases of soybeans. Learn more about the diseases that affect plants, ranging from garden flowers to food crops. |
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Phytophthora Damping Off and Root Rot of Soybean
Submit your comments, tips, or suggestions you'd like to share with other users regarding this article. Reference: Ohio State University Extension Phytophthora damping off and root rot are destructive diseases of soybeans. When rainfall saturates fields soon after planting, severe seedling kill can result in yield losses greater than 50% in individual fields. Phytophthora seed
The disease is most severe in poorly drained soils with high clay content. Traditionally, the northwest section of the state has had severe problems with Phytophthora damping off and root rot. With the increased use of no-tillage and reduced tillage residue management systems, however, Phytophthora damping off and root rot has become a serious problem in other areas as well. The soil-borne pathogen that causes this disease (Phytophthora sojae) can be found in most agricultural soils in the state. Symptoms
Phytophthora can attack soybean plants at any stage of development. Symptoms in young plants include rapid yellowing and wilting accompanied by a soft rot and collapse of the root. More mature plants generally show reduced vigor and may be gradually killed as the growing season progresses. Foliar symptoms on older plants occur as general yellowing of the lower leaves that progresses upward on the plant, followed by wilting and death. The root system is usually severely affected such that lateral and branch roots are almost completely discolored. Tap roots show a brown discoloration on the surface and, if split, the inner tissues show a tan to brown discoloration. Perhaps the best diagnostic symptom of the disease on susceptible varieties is a lower stem discoloration that may extend several nodes up the stem. Symptoms on varieties with partial resistance are not as evident as on highly susceptible varieties. When the soil becomes saturated soon after planting, varieties with partial resistance may be subject to damping off and root rot. However, when infections occur later in the season, the extent of the root damage will be restricted, and there will be no development of the girdling stem lesions as in susceptible varieties. The Pathogen Conditions favorable for infection occur most often on heavy clay soils with poor drainage. Phytophthora can attack plants at soil temperatures above 50 degrees F, but severe disease generally occurs when soil temperatures are 60 degrees F or above.
Phytophthora exists in soils as populations of different races. Over 70 different races of P. sojae have been detected in Ohio soils. P. sojae has been recovered from 82 of 86 fields taken from 20 Ohio counties. The tremendous variability in the P. sojae populations from these fields indicate that many Rps genes are no longer effective. The final outcome is that P. sojae populations in Ohio have adapted to many of the commercial Rps genes that are currently available in soybean cultivars.
Phytophthora sojae populations are in the midst of a race shift in Ohio. This means that not every individual can cause disease on a plant with an Rps gene. Figure 4 illustrates a P. sojae population in one field where 100 soil cores were collected, spaced 100 feet apart. P. sojae could be recovered from 82 of the 100 cores indicates a very high population. Next we analyzed this field for race type or pathotype. The squares indicate those locations where the P. sojae killed plants with the Rps1k gene; circles, Rps1c; and stars, Rps3a. From this field map we can see that any single gene would provide protection in 50% of the locations in the field, but not all. Management
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| Data Source: Ohio State University Extension. Articles and resource may contain pesticide recommendations that are subject to change at any time. These recommendations are provided only as a guide and it is always the pesticide applicator's responsibility, by law, to read and follow all current label directions for the specific pesticide being used. |
