What Is Belly Rot: Tips On Avoiding Rotting Vegetable Fruit

Brown Rotted Spot On Vegetable
belly rot cucumber
(Image credit: Clemson University - USDA Cooperative Extension Slide Series, Bugwood.org)

An overeager cucurbit producing bushels of cucumbers, melons, or squash feels like a plague in the garden by midsummer, but there are worse things that can happen. Rotting vegetable fruit, caused by rhizoctonia belly rot, is one of those things. As difficult as disposing of healthy vegetables can be when your zucchini explodes into life, it's a much bigger task dealing with bad fruits.

What is Belly Rot?

Belly rot in fruit is caused by the fungus Rhizoctonia solani, which survives in the soil from year to year. The fungus becomes active when humidity is high and temperatures warm, causing obvious signs of infection within 24 hours and entirely rotting fruits in as little as 72. Temperatures below 50 degrees F. (10 C.) can slow or prevent infection. This is primarily a disease of cucumbers but may cause belly rot in fruit of squash and melons as well. Fruits that are in direct contact with the soil develop small, tan to brown water-soaked spots on the ground spot. As the disease spreads, the spots expand and become crusty and irregularly shaped. An advanced case of rhizoctonia belly rot causes these spots to sink, crack, or appear crater-like. Flesh near the lesions is brown and firm, sometimes extending into the seed cavity.

Preventing Rotting Vegetable Fruit

Crop rotation is one of the best ways to prevent rhizoctonia belly rot, especially if you rotate with grain crops. If your garden is small, though, crop rotation may be difficult. In that case, you must do what you can to minimize contact between fruits and fungal structures. Start by tilling your garden deeply, or even double-digging when possible. The deeper you can bury the fungus in the soil, the less likely you'll be bothered by it. Once plants are growing, a thick, black plastic mulch can prevent fruit from contacting the soil directly, but you must still water carefully to avoid over saturating the fruits or the soil. Some gardeners put their young fruits onto small mounds made from wood, shingles, wire, or mulch but this can be labor intensive. Another way to get your fruits off the ground is to train them to a trellis. Not only does trellising save space, it can prevent many different problems caused when fruits are in contact with the soil. Trellises keep your beds tidy and fruits within easy reach for harvesting. Just remember to support growing fruits with stretchy hammocks made from material such as pantyhose.

Kristi Waterworth

Kristi Waterworth was a regular contributor to Gardening Know How for many years, answering countless queries on plant pests and diseases.