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Weather and pests can make summer squash a frustrating crop for home gardeners By Sharon Dowdy

Pests and diseases make summer squash one of the most challenging vegetables to grow in Georgia home gardens, according to University of Georgia plant pathologist Elizabeth Little, who studies plant diseases and control methods at the UGA College of Agricultural and Environmental Sciences.

“Through my plant pathology experience and observations, I’ve noticed what is most difficult to grow in Georgia’s hot, muggy summers. Squash tops the list,” Little said. “That’s why summer squash will grow better where summer conditions are cooler and drier.”

Insects like squash vine borers and squash bugs often dine on summer squash.

Squash vine borer moths lay eggs at the base of the squash plant and the larvae feed within the stem. Their feeding damages the plant, causing it to wilt and collapse. The only sign of the pest is sawdust-like frass at the base of the stem. 

There is no guaranteed way to control squash vine borers aside from planting a resistant variety of squash. UGA Cooperative Extension horticulturist Bob Westerfield tells backyard gardeners to plant extra squash plants, “some for you and some for the squash vine borers.”

In May, squash bugs lay eggs in the first planting of summer squash and remain in the garden. They can carry a bacterial disease that causes the plants to wilt and die, Little said.

“Insects can be seen on plants, but diseases are a little mysterious,” she said. “You can’t just look at the plant and see the microscopic pathogens.”

Viruses often knock out summer squash plants during July and August. To fight viruses, Little suggests that home gardeners plant an early crop of squash, then wait until the fall and plant again. 

Many squash diseases strike plants by July and August. The key is to stay ahead of the diseases, Little said. Choose an open, sunny spot and plant early in the season. Keep plants healthy through good fertility and soil conditions, she said. 

“If you wait until after you see the disease, it’s too late,” she said. “It’s all about prevention. There is no cure.”

Downy mildew, a water mold, can also be a problem in summer squash, according to Little. The mold hurts the leaves of the plant, which affects photosynthesis.

Downy mildew doesn’t survive over the winter, but it moves from south Georgia each year and shows up in north Georgia by June or July, she said.

“It’s not an early-season disease, so planting early can help,” she said.

Powdery mildew loves Georgia’s hot, humid summers and summer squash. Some squash cultivars were bred with resistance to the disease.

To help cut down on disease pressure in the home garden, have a “squash-free period” during the height of summer. This helps stop the cycle of pests and disease, Little said.

Fruit can start to rot during wet weather. To fight fruit rot, improve air circulation in the garden by making sure plants are not crowded. Keep the fruit dry and off the ground by placing leaves or landscape cloth under the fruit. 

In general, Little recommends that backyard gardeners search for vegetable varieties that grow best in hot environments. 

Tomatoes and pumpkins are also on Little’s list of vegetables that are hard to grow in Georgia due to pests and diseases, but she says that watermelons and other melons grow well in Georgia heat.

For more information on growing a vegetable garden in Georgia, read through the UGA Extension publications at www.extension.uga.edu/publications.

(Sharon Dowdy is a news editor with the University of Georgia College of Agricultural and Environmental Sciences.)

Yellow squash
Yellow squash

A yellow squash matures on the vine of a squash plant growing in Butts County, Georgia.

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A yellow squash matures on the vine of a squash plant growing in Butts County, Georgia. Download Image
Squash vine borer damage
Squash vine borer damage

Squash vine borer larvae hatch and eat their way into the plant's stem near the soil level. Since the pests are hidden inside the plant, most home gardeners have no idea that pests are present until the plants wither and die. A healthy squash plant (left) is shown in a Spalding County, Georgia, garden next to a plant infected with squash vine borers.

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Powdery mildew and virus on summer squash
Powdery mildew and virus on summer squash

This squash plant has powdery mildew and a virus. The powdery mildew is more obvious, as it has caused the leaf to turn white. The virus has distorted the leaves of the squash plant.

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