Why Does Squash Shrivel on the Vine?

Squash is usually an easy crop to grow, needing only rich soil, moisture and sunlight to produce a bountiful crop. Occasionally, though, squash may shrivel and drop from the vine due to disease or cultural problems. Summer squash grows quickly and is less susceptible to disease and insect damage than winter squash, which requires a long growing season.

Squash is usually pollinated by bees, but pollination may be poor if few bees are out due to cold, rainy weather or pesticide damage. When the plants are poorly pollinated, the squash fruits shrivel and drop off the vine while still young. Hand-pollinate squash during an extended rainy period. Find a male blossom, identified by the lack of a bump between the flower and the vine. Remove the petals, leaving the stamen, or stalk in the middle of the flower. Rub the stamen over the stigma, or inner portion of a female blossom, to pollinate it, resulting in better fruit production. Identify female blossoms by the small bump behind the flower.

Diseases, such as powdery mildew and fruit rot, may cause the squash to shrivel and drop from the vine. In this case, though, you'll notice other symptoms. Powdery mildew causes a white growth on the leaves and vines, while fruit rot causes black fungus to grow on the squash. Control these diseases through the use of fungicides. Space the plants so air circulates freely and use soaker hoses to keep the leaves dry.

Boring insects and cucumber beetles can cause considerable damage to squash plants. Squash vine borers are the larvae of squash vine moths. They bore into the vines, leaving sawdustlike dust on the soil. The vines eventually collapse and the squashes shrivel and die. Cucumber beetles cause damage by eating the vines, leaves and fruit and are also the vectors of many diseases. Spray for insects early in the season when they are young.

Poor pollination is difficult to predict and control, but good growing practices help minimize disease and insect problems. Rotate crops so squash doesn't grow in the same location each year. Plant disease-resistant varieties and remove plants that show signs of insect and disease problems.