This is especially true if you are growing more than one type of squash or a hybrid squash. Q. My squash leaves are covered with a white, powdery substance. The plants die rapidly. This is powdery mildew, a fungal disease that attacks squash and kills the plants. Some varieties tolerate this disease better than others.
Powdery mildew is more of a problem in the fall than in the spring.
The most effective fungicide control is benomyl or Benlate. Mildew occurs most often on old foliage of declining plants. Succession plantings of squash will provide vigorous, productive plants and allow removal of older, more susceptible plants. Q. My fruit blooms and sets young fruit, yet quickly becomes covered with a black, whiskery fungal growth. This is Chaonephora fruit rot, a soilborne disease which rots the young fruit and is particularly damaging during extended wet periods.