Why Do Some Snap Beans Curl While Growing?

Growth Requirements

• Plenty of even moisture and lots of heat are key to successful snap bean production. Temperatures between 70 and 85 degrees Fahrenheit are ideal, but hotter temperatures can cause leaves and fruit to drop or wilt. Curling or deformed pods may occur when moisture is inadequate or as a result of poor soil or insect attack. A pH of 6.0 to 6.5 will help beans obtain the nutrients they need to grow long and healthy.

Disease

• Mosaic viruses, which incorporate 10 different strains, are sometimes the culprit of unhealthy bean plants and deformed bean pods. The diseases cause stunted plants that appear mottled, with patches of light green and yellow in between dark green. Leaves may grow longer and curl at the tips, while pods are deficient in size and sometimes curl as well. Many snap bean cultivars are resistant to the BCMV -- bean common mosaic virus -- strain of the virus. These include Bush Blue Lake, Larma, Mikado, Provider, Contender, Rebel and Lake Superior.

Pests

• A few notable pests can hinder healthy development and lead to curling pods on a bean plant. Many growers believe that thrips, slender winged insects, create deformed foliage and fruit when they munch on plant tissue while it is still developing. If plants in your garden consistently emerge with deformed leaves and pods, it may be a sign that the shoots of the leaves were damaged by thrips. Aphids may also be causing the harm. These tiny green, black or yellow insects may feed heavily on leaves and cause foliage and fruit to deform and curl.

Straight Pods

• A healthy plant free of diseases and environmental disruption will generally produce straight, green and crisp pea pods. Almost any kind of trauma to the plant's health can cause curling pods. In one study, an application of an herbicide, Clopyralid, caused mild pod curling in snap beans. Lack of moisture and proper fertilizer may also prevent the plant from developing full-sized, straight beans, so a healthy environment is key. To prevent pest infestation that could lead to curling pods and yield loss, apply a safe or organic pesticide.