EFFECTS OF THE FREQUENCY OF FURROW IRRIGATION ON ROOT AND FRUIT ROTS OF SQUASH CAUSED BY PHYTOPHTHORA-CAPSICI

Squash (Cucurbita pepo var. melopepo cv. Early Summer Crookneck) was g rown from seed in field plots initially free of Phytophthora capsici a t Davis, California. Thirty to forty days after seeding, the soil adja cent to the plants in half of the plots was infested with P. capsici p ropagules. Furrow irrigation was applied uniformly before the soil was infested and every 7, 14, or 21 days thereafter, for both infested an d noninfested plots. Disease progress was significantly slower, onset of disease was delayed, and final severity of symptoms on shoots and r oots was significantly reduced with decreasing frequency of irrigation . Yields in infested soil irrigated every 14 and 21 days did not diffe r from the yields obtained in the corresponding noninfested controls. In contrast, the yield in infested soil irrigated every 7 days was onl y 40% of the yield obtained in the corresponding controls. Yield losse s due to the direct infection of fruit were limited to 20% by weight, and the results suggested that root and shoot symptoms had to become s evere for yield loss to be significant. In the absence of the pathogen , irrigation frequency had no significant effect on yield or plant wat er potential, and plants irrigated less often extracted water from dee per soil layers. The results imply that less frequent furrow irrigatio n is an effective way to reduce losses due to P. capsici in squash fie lds in California.