Rhizoctonia root rot is caused by the fungus Rhizoctonia solani. The fungus survives in infected plant debris, and inoculum concentrations in the soil are increased by continually cropping fields to susceptible crops such as dry bean, potato and sugarbeet. Rhizoctonia is spread within and between fields by irrigation water and soil movement. Rhizoctonia root rot of germinating seedlings is favored by moderate to high soil moisture and low soil temperatures. Damage is generally restricted to young seedlings, but can affect older plants, especially when the plants are stressed by extremes in temperature between warm soil and cool water from deep irrigation wells.
Rhizoctonia solani can cause seedling death, root and hypocotyl rot, stem cankers and pod rot. Initial symptoms appear on roots or hypocotyls as linear or circular reddish-brown sunken lesions or cankers delimited by a brown to reddish-brown margin. Rhizoctonia cankers enlarge with age, become darker, rough textured, and retard plant growth. The fungus can invade the central part of the lower stem and produce a brick-red discoloration. Disease symptoms often occur on scattered plants in a somewhat circular field pattern. Severe seedling infection causes plant death. Rhizoctonia cankers enlarge with age, become darker, rough textured, and retard plant growth. Later in the season, mixed infection with Fusarium and Pythium root rot organisms are common. Lesions may also develop on pods that are in contact with the moist soil surface and cause pod rotting or seed discoloration.
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 excess irrigation and poor drainage. Crop rotation with non-hosts (i.e., small grains) may provide some reduction in Rhizoctonia root rot. Conventional tillage that incorporate previous crop residue deeply and early can to promote complete decomposition before planting and reduce Rhizoctonia root rot.
Chemical controls are most effective when combined with sound cultural practices.
Product List for Rhizoctonia Root Rot:
Pesticide |
Rate per 100 lb seed |
Application Frequency (days) |
Remarks |
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Azoxystrobin |
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Amistar |
0.125-0.25 oz/1000 ft |
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Quadris |
0.4-0.8 fl oz/1000 ft |
Planting time treatment |
Suppression of Rhizoctonia spp. |
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Captan |
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Captan 75 |
6-9 oz |
Seed treatment |
Broad spectrum, but weak against Pythium spp. |
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Captan 30-DD |
1.33-2.33 fl oz |
Seed treatment |
Broad spectrum, but weak against Pythium spp. |
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Captan 400 |
1.5-3.0 fl oz |
Seed treatment |
Broad spectrum, but weak against Pythium spp. |
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Captan 400-C |
1.5-3.0 fl oz |
Seed treatment |
Broad spectrum, but weak against Pythium spp. |
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Fludioxinil |
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Maxim 4FS |
0.08-0.16 fl oz |
Seed treatment |
Suppression of Fusarium and Rhizoctonia spp. |
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Fumigants |
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Telone II |
9-15 gal |
Restricted use; Preplant application, aerate 7-14 days. |
Broad spectrum |
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Telone C-17 |
10-17 gal |
Restricted use; Preplant application, aerate 7-14 days. |
Broad spectrum |
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Vapam |
40-100 gal |
Restricted use; Preplant application, aerate 7 days. |
Broad spectrum |
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Metalaxyl/Mefenoxam |
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Apron XL LS |
0.085-0.64 fl oz |
Seed treatment |
Suppression of Pythium and Phytophthora spp. |
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Allegiance-FL |
0.75 fl oz |
Seed treatment |
Suppression of Pythium and Phytophthora spp. |
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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. |
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Ultra Flourish |
2-4 pts |
Pre-plant incorporated drench or 7” soil band |
Suppression of Pythium and Phytophthora spp. |
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Thiram |
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42-S Thiram |
4.5 fl oz |
Seed treatment |
Broad spectrum |
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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, Rhizoctonia Root Rot
Date: 04/06/2007