Phytophthora capsici
.jpg "Phytophthora capsici causing pumpkin fruit rot")
Phytophthora capsici causes 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. P. capsici is the most commonly encountered species but P. parasitica, P. cactorum and other species may occasionally occur. 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. For instance, snap bean has been reported as new host of P. capsici in 2008 and 2009.
P. capsici can cause both root and crown rot as well as fruit rot in all species of cucurbits. Initial symptoms of crown rot are a sudden, permanent wilt of infected plants. The roots and stems near the soil line become water-soaked, dark brown, and soft. Infected stems collapse rapidly and the root system is completely destroyed. Fruit can become infected at any stage of maturity by soil contact or rain-splash. Initial symptoms on the fruit are small areas of water-soaking that quickly enlarge and become covered with sporangia which give the fruit a yeast-like, gray to white appearance.
P. capsici is a soil-borne fungus, thus it has the ability to survive for many years in the soil and the disease can be expected to reoccur when conditions are favorable. Optimum conditions for disease are saturated soil and relatively warm temperatures. Care should be taken to avoid spreading the pathogen into new areas on the farm. The pathogen reproduces by both sexual and asexual means. Oospores are the sexual stage that overwinter in the soil and provide initial inoculum for disease initiation. P. capsici is dependent on ample soil moisture to cause disease. After soil is saturated for a number of hours, sporangia form and the motile zoospores (asexual stage) are released. The zoospores are attracted to the living plant parts in or on the surface of the soil. When soil moisture is limiting, P. capsici causes little if any disease. Oospores, the survival and overwintering stage of the pathogen, can survive in the soil for up to ten years in the absence of a susceptible crop. P. capsici spreads within fields primarily with water; rain splash from soil in the row or between rows to foliage and fruit causes new infections.
Yield is reduced by both infected fruit and loss of production fromaffected plants. Complete loss of the crop can occur when infection is severe.
- Scout fields for symptoms on a regular basis, especially after heavy rainfall and in areas of poor drainage.
- Avoid introducing Phytophthora into uninfested fields. After working in Phytophthora-infested soil, wash soil from equipment. Always work in clean fields first.
- No effective rotation period has been established, though University researchers currently recommend a rotation away from susceptible crops for at least three years. Two years has proven to be ineffective.
- Plant resistant varieties whenever possible. Pumpkins with hard, gourd- like rinds or shells are less susceptible to Phytopthora fruit blight. Lil' Ironsides, Apprentice, IronMan, Rockafellow, CannonBall have been reported as moderately resistant. IronMan, CannonBall, and Rockafellow also possess Powdery Mildew resistance.
- Avoid planting susceptible crops in Phytophthora infested soil. Rotate with corn or small grains. If this is not possible, follow the cultural practices outlined.
- Water management is critical to reduce Phytophthora epidemics. Both rainfall and irrigation have large impacts on the time of onset and severity of Phytophthora Blight epidemics. Disease incidence can be very high after heavy rainfall and frequent drip irrigation.
- Avoid planting in low areas of a field. Avoid standing water in fields.Check irrigation system for leaks and eliminate them.
- In some soils, installation of drainage systems may be warranted. Deep plowing with a V-ripper can increase drainage enough to minimize disease.
- Splash dispersal of inoculum can be reduced by straw mulch between rows or on bare soil with stubble from a cover crop. Inoculum can move rapidly on black polyethylene mulch and bare soil.
- Combining no-till cover crop production with moderately resistant varieties can reduce fungicide inputs, resulting in reduced production costs and delay the development of fungicide resistance in pathogen populations.
- When symptoms are localized in a small area, disking the area may be worthwhile. Start with a border of healthy plants.
- No fungicide has been shown to be sufficiently effective to be the sole management strategy for Phytophthora diseases, however when used in conjunction with cultural practices they can be a valuable tool.
For Current information on disease recommendations ins specific crops including information on chemical control & pesticide management, please visit the New England Vegetable Management Guide website.
Diseases
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