Pythium root rot and wilt is caused by various fungus-like pathogens in the genus Pythium. The diseases are favored by high soil moisture and moderate to high temperature. Varietal susceptibility will also influence disease development. Pathogen survival and inoculum buildup are favored by soils with high organic matter and poor drainage. Susceptibility can be increased if roots are damaged during cultivation or by other soil related problems, such as nematode feeding. The fungus can be transported within and between fields by contaminated irrigation water. Occurrence is also favored by improper crop rotation. The pathogen survives pathogenically on weeds and in the soil as dormant oospores.
Pythium species may infect planted seeds prior to germination, germinating seedlings, young plants, or older plants during blossoming and pod formation. It is one of the pathogens capable of causing seed decay and seedling death. Initial root rot symptoms appear as elongated water-soaked areas on the hypocotyl and roots, within one to three weeks after planting. The pathogen will extensively prune roots, reduce overall plant growth, and destroy much of the hypocotyl and main root system. The water-soaked region may extend several inches above the soil line, with little, if any, visible evidence of the fungus. The water-soaked area eventually dries out, becomes somewhat sunken, and tan to brown in color. Plants then wilt and die. Disease development later in the season results when pods in contact with the soil become infected. These pods exhibit a watery soft rot, or a mass of white fungal growth, but black sclerotia do not form as with white mold.
Deny (Burkholderia cepacia) is registered for protection of dry bean roots from Fusarium, Rhizoctonia, and Pythium spp. T-22 Planter Box (Trichoderma harzianum strain KRL-AG2) is registered, but cannot by used in alkaline or cold soils. The efficacy of these biological control agents in the High Plains is not known.
Plant high quality seed in warm (greater than 60°F), well-prepared seedbeds under conditions favorable to rapid seedling emergence; shallow planting can encourage rapid emergence. Avoid excessive irrigation and poor drainage. Planting into raised beds can help avoid water- logging and promote more rapid germination. Crop rotation with non-hosts (i.e., small grains) may provide some reduction in damping-off pathogens, but damping-off and seedling blight pathogens have very broad host ranges and can attack most plants. Conventional tillage tends to reduce damping-off as compared to minimum or no-till operations. Where pod rot is a problem, irrigation intervals should be extended near the end of the season to allow the soil surface to dry, thus inhibiting fungus development.
Chemical controls are most effective when combined with sound cultural practices.
Product List for Pythium Wilt and Root Rot:
Pesticide |
Rate per 100 lb seed |
Application Frequency (days) |
Remarks |
|
Captan |
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Captan 75 |
6-9 oz |
Seed treatment |
Broad spectrum, but weak against Pythium spp. |
|
Captan 30-DD |
1.33-2.33 fl oz |
Seed treatment |
Broad spectrum, but weak against Pythium spp. |
|
Captan 400 |
1.5-3.0 fl oz |
Seed treatment |
Broad spectrum, but weak against Pythium spp. |
|
Captan 400-C |
1.5-3.0 fl oz |
Seed treatment |
Broad spectrum, but weak against Pythium spp. |
|
Fludioxinil |
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|
Maxim 4FS |
0.08-0.16 fl oz |
Seed treatment |
Suppression of Fusarium and Rhizoctonia spp. |
Fumigants |
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|
|
|
Restricted use; Preplant application, aerate 7-14 days. |
Broad spectrum |
|
Telone C-17 |
10-17 gal |
Restricted use; Preplant application, aerate 7-14 days. |
Broad spectrum |
|
Vapam |
40-100 gal |
Restricted use; Preplant application, aerate 7 days. |
Broad spectrum |
|
Metalaxyl/Mefenoxam |
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|
Apron XL LS |
0.085-0.64 fl oz |
Seed treatment |
Suppression of Pythium and Phytophthora spp. |
|
Allegiance-FL |
0.75 fl oz |
Seed treatment |
Suppression of Pythium and Phytophthora spp. |
|
Ridomil Gold EC |
0.5-2 pts |
Pre-plant incorporated soil drench or soil band (a 7” band is recommended) |
Suppression of Pythium and Phytophthora spp. |
|
Ultra Flourish |
2-4 pts |
Pre-plant incorporated drench or 7” soil band |
Suppression of Pythium and Phytophthora spp. |
|
Thiram |
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42-S Thiram |
4.5 fl oz |
Seed treatment |
Broad spectrum |
|
Thiram 50WP |
4.5 oz |
Seed treatment |
Broad spectrum |
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The information herein is supplied with the understanding that no discrimination is intended and that listing of commercial products, necessary to this guide, implies no endorsement by the authors or the Extension Services of Nebraska, Colorado, Wyoming or Montana. Criticism of products or equipment not listed is neither implied nor intended. Due to constantly changing labels, laws and regulations, the Extension Services can assume no liability for the suggested use of chemicals contained herein. Pesticides must be applied legally complying with all label directions and precautions on the pesticide container and any supplemental labeling and rules of state and federal pesticide regulatory agencies. State rules and regulations and special pesticide use allowances may vary from state to state: contact your State Department of Agriculture for the rules, regulations and allowances applicable in your state and locality. |
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Categories: Dry Bean, Disease, Pythium Wilt, Root Rot
Date: 04/01/2007