Pepper Phytophthora
PHYTOPHTHORA BLIGHT OF CUCURBITS, PEPPERS AND TOMATO
Several different species of Phytophthora cause a root, crown and fruit rot of cucurbits, tomato, pepper and eggplant. Root and crown rot are particularly destructive because the entire plant collapses. When the disease occurs on cucurbit fruit, a white to gray mealy growth develops on the surface. This is the reproductive phase of the pathogen that allows for dissemination of spores during rain. On tomato, a firm brown lesion "buckeye rot" develops on fruit in contact with the ground. Planting into contaminated soil, especially under moist conditions can result in a high incidence of seedling rot.
Phytophthora is a soil-borne fungus, thus it has the ability to survive for many years in the soil. Care should be taken to avoid spreading the pathogen into new areas on the farm. Phytophthora is dependent on ample soil moisture to cause disease. After soil is saturated for a number of hours, motile zoospores are released. The zoospores are attracted to the living plant parts in or on the surface of the soil. When soil moisture is limiting, Phytophthora causes little if any disease.
Phytophthora capsici is the most commonly encountered species but P. parasitica, P. cactorum and other species may occasionally occur. Phytophthora parasitica has a fairly wide host range including bean, eggplant, honeydew melon, onion, parsley, peppers, rhubarb, strawberry, pumpkin, tomato, tobacco, turnip and watermelon. Because there is some variation in the host range of Phytophthora species, it is useful to know what species are present. However, host lists of these and other plant pathogens should be viewed as incomplete because new hosts are occasionally found. Specimens should be sent to the address listed above for verification. Confirmation of Phytophthora takes several days but species identification takes several weeks.
Management
- Avoid planting susceptible crops in Phytophthora infested soil. Rotate with corn or small grains. If this is not possible, follow the cultural practices outlined below.
- Where crown rot is a problem, plant peppers dome-shaped raised beds. This allows the soil to dry more quickly after rains. Raised beds that sag in the middle or around the plant will not be effective. After forming beds it is important to allow for the water to drain from the end of the rows. Raised beds will not work for vine crops.
- In some soils, installation of drainage systems may be warranted. Deep plowing with a V-ripper can increase drainage enough to minimize disease. In cucurbits, subsoil between rows before the crop vines over.
- Do not use plastic mulch unless it is in conjunction with dome-shaped beds.
- After working in Phytophthora-infested soil, wash soil from equipment. Always work in clean fields first.
- When symptoms are localized in a small area, disking the area may be worthwhile. Start with a border of healthy plants.
- Scout fields for symptoms on a regular basis, especially after heavy rainfall and in areas of poor drainage.
- No fungicide has been shown to be sufficiently effective to be the sole management strategy for Phytophthora diseases, when used in conjunction with cultural practices they can be a valuable tool.
Chemical recommendations:
Cupric hydroxide (Kocide): 11/2 to 3 TBSP/1000 sq ft (0 dh, REI 24 h). For foliar and fruit phases of diseases ONLY. Do not apply in a solution having a pH less than 6.5 as phytotoxicity may occur.
Dimethomorph plus mancozeb (Acrobat 50 WP): 6.4 oz/A (4 dh, REI 12 h).Begin applications before symptoms occur and repeat on a 5-10 day interval depending on whether conditions are favorable and symptoms present. Tank mix with a broad spectrum fungicide (chlorothalonil or maneb). Do not apply more than 5 times per season.
Hydrogen dioxide (OxiDate): ½ to 1 gallon/A in 50-200 gallons water. (0 dh, REI 1 h).Provides quick kill of contacted spores with NO residual activity.
Mefenoxam (Ridomil Gold): 1 pt/A. (7 dh, REI 48 h). For crown rot phase in peppers and root/fruit rot of tomatoes. Apply preplant or at planting followed by 2 post-directed applications at 30 day intervals. Applications must be incorporated mechanically or by irrigation.
Mono- and di-potassium salts of phosphorous acid (Fosphite): 1-3 qt/A in 100 gallons of water. (0 dh, REI 4 h). Apply prior to disease development and continue at 2-4 week interval. Use higher rate when disease pressure is severe. Do not apply more than 6 times per season.
Sodium, potassium, ammonium phosphites (Phostrol): 2.5 to 5 pt/A (0 dh, REI 4 h).Begin when conditions favor disease development and continue at 7-14 day interval. Use higher rate and shorter interval where disease pressure is severe. Mixing of Phostrol with other products may increase salt content and the potential for fruit burn.
Zoxamide plus mancozeb (Gavel 75 DF): 1.5 to 2.0 lb/A (5 dh, REI 48 h).Not registered for pumpkin or Peppers. Apply at a 7-10 day interval when conditions are favorable for disease development. Use sufficient water and direct sprays to provide thorough coverage. Do not apply more than 8 times per season.
Prepared by Dr. Robert L. Wick, Department of Plant, Soil and Insect Science and M. Bess Dicklow, UMass Extension, Fernald Hall, Room 111, University of Massachusetts, Amherst, MA 01003. Tel. (413) 454-1045, 413-577-1827 Fax (413) 545-2115. rwick@psis.umass.edu, mbdicklo@umext.umass.edu
Revised August 2005 V2
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