Soil, Crop and Pest Management

Phytophthora Blight of Cucurbits, Peppers and Tomato

Prepared by Dr. Robert L. Wick, Department of Microbiology, Fernald Hall, Room 111, University of Massachusetts, Amherst, MA 01003. Tel. (413) 454-1045 Fax (413) 545-2532

Revised September 30, 1997 V1

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

1. 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.
2. 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.
3. In some soils, installation of drainage systems may be warranted. Deep plowing with a V-ripper can increase drainage enough to minimize disease.
4. Do not use plastic mulch unless it is in conjunction with dome-shaped beds.
5. After working in Phytophthora-infested soil, wash soil from equipment. Always work in clean fields first.
6. For protection against the foliar and fruit phase of the disease which occurs later in the growing season, apply cupric hydroxide (Kocide® 101): 2 lb/A every 7-10 days.