Water management in relation to control of Phytophthora capsici in vegetable crops

Moisture, as free water or atmospheric humidity, is a driving force in the biology and ecology of Phytophthora capsici. Free water and soil matric potential are significant factors affecting mycelial growth, sporangial formation, zoospore release, and oospore production of this pathogen. Soil moisture and relative humidity in the atmosphere are critical in determining survival of mycelium and other propagules in the soil and on the plant. Plant infection by P. capsici and disease development are favored by rainfall and high soil moisture, and periodic flooding contributes to a more severe disease. Movement of surface water in the field plays an important role in dispersal of P. capsici and disease increase, and atmospheric humidity affects development of fruit rot. Contamination of irrigation water sources with P. capsici has been reported in a few states in the United States, and limited studies have been conducted to develop tactics to mitigate the impact of contaminated irrigation water. Proper irrigation management and other cultural practices should be implemented to reduce incidences of the disease, such as raised beds, mulching, irrigation methods, and avoidance of excess water. Effect of irrigation water quality on disease development merits further study and developing comprehensive moisture-based forecasting models would help predict disease epidemics and timely application of management approaches.