Phytophthora blight is caused by the fungus-like organism Phytophthora capsici, and is a widespread and often devastating disease of pepper and occasionally tomato and eggplant. The pathogen has a broad host range and can attack many vegetable crops, including cucumber, melon, squash, and pumpkin. P. capsici can reproduce sexually (oospores) and asexually (zoospores and sporangia). Sexual oospores can persist in the soil for several years, and serve as initial inoculum. Asexual zoospores and sporangia are easily disseminated by wind, splashing rain, and irrigation water. When zoospores or sporangia make contact with a plant, they can infect any tissue. The pathogen survives between susceptible crops in the soil as oospores and in contaminated seed.
Phytophthora blight can affect all plant parts. Root infections generally appear as blackening of roots and crowns, causing a wilting of the plant. Stem infections appear as distinctive black lesions. When spores are splashed from the soil onto leaves, water-soaked spots form and enlarge quickly into pale green to brown lesions. Lesions are often covered with white sporangia in moist weather, especially on the bottom sides of leaves. Infected foliage becomes brown, shrivels, and soon dies. Infected fruit are typically covered with white sporangia and shrivel. The disease can be devastating when conditions favor the pathogen; complete crop losses can occur in heavily infested fields.
Soil solarization and incorporation of organic amendments can reduce soil inoculum levels and subsequent disease development.
Plant high quality seed free from P. capsici. Plant into well-prepared raised beds and evenly leveled fields that promote rapid drainage of irrigation and rain water. Use drip rather than sprinkler or furrow irrigation if possible. Prevent excessive moisture. Avoid planting into fields with known salinity problems. Straw mulches reduce splash dispersal of soilborne inoculum and can reduce foliar infection. Practice a three-year or longer crop rotation between susceptible crops. Plant resistant or tolerant varieties if available.
P. capsici resistance to metalaxyl and mefenoxam is widespread in some regions, and alternative fungicides and disease management strategies should be used if resistant strains are present.
Product List for Phytophthora Blight:
Pesticide |
Product per acre |
Application Frequency (days) |
Remarks |
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Famoxadone/Cymoxanil |
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Tanos |
8 oz |
5-7 days |
Rotate and rotato with fungicides with a different mode of action such as chlorothalonil or mancozeb; Maximum of 72 ounces per season; 3 day PHI |
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Mefenoxam |
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Ridomil Gold EC |
1-2 pts |
Broadcast or banded at planting; Maximum of three injections by drip irrigation; maximum of three pts per season; 7 day PHI |
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Ridomil Gold GR |
20 lbs |
Band (7”) or broadcast and incorporate with 0.5 to 1” of irrigation water; a second application can be made; 7 day PHI |
Maximum of 40 pounds per season; 7 day PHI |
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Ridomil Gold/Bravo |
1.5-2.0 lb |
7-14 days |
Make 3 total sprays; 14 day PHI |
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Ridomil Gold/Copper |
1 pack/per 2.5 acres |
5-14 days |
Make 3 total sprays; 14 day PHI |
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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: Eggplant, Pepper, Tomato, Disease, Phytophthora Blight, Phytophthora Fruit Rot
Date: 04/01/2007