Phytophthora capsici
Phytophthora crown rot and foliar blight of peppers caused by Phytophthora capsici has become one of the most devestating diseases of solanaceous and cucurbit crops. Prevention is the key to managing P. capsici because the disease is difficult to suppress with fungicides once it develops. Fields free of P. capsici should remain so unless equipment carrying clods of soil bring it into new sites. It is possible that contaminated irrigation water can introduce the fungus to new sites but it is very difficult to detect Phytophthora in irrigation water. The pathogen is not likely to be seed-borne in commercial seed, and it does not travel easily through the air for long distances.
P. capsici causes a root and crown rot of pepper and produces distinctive black lesions on stems. Root infection leads to wilt and eventual death of plants. The pathogen also infects leaves causing water-soaked, circular, brown lesions. Leaf and stem lesions often result fromsplash dispersal of the pathogen onto the lower portions of the plants. Fruit can also be infected resulting in lesions similar to leaf lesions. In high humidity, lesions may be covered with white sporangia.
This soil-borne fungus can survive many years in the soil as Oospores (survival structures resistant to adverse environmental conditions) and the disease can be expected to reoccur when conditions are favorable. Optimum conditions for disease are saturated soil and relatively warm temperatures. The pathogen reproduces by both sexual and asexual means. Oospores are the sexual stage that overwinters 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.
Yield is reduced by both infected fruit and loss of production fromaffected plants. Complete loss of the crop can occur when infection is severe.
- Avoid planting susceptible crops in P. capsici infested soil. Rotate with corn or small grains. If this is not possible, follow the cultural practices outlined below.
- Rotate out of susceptible crops (cucurbits, peppers, tomatoes) for at least three years.
- Resistant or tolerant varieties of pepper, i.e. 'Paladin' are available.
- 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.
- Avoid standing water by subsoiling or chisel plowing, leveling the field, or constructing trenches and waterways to improve drainage. If necessary, subsoil during the growing season, especially after rain.
- In some soils, installation of drainage systems may be warranted. Deep plowing with a V-ripper can increase drainage enough to minimize disease.
- Practice good sanitation and do not discard cull fruit in the field.
- 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 P. capsici. When fungicides are 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
Get real-time updates from the field on emerging pests, upcoming meetings, and extension projects on our Facebook page!
