If you’re growing green beans, you may notice that the leaves have more holes than leaves, and the pods aren’t much better either. The culprit is likely the bean leaf beetle, Cerotoma trifurcata. This chrysomelid beetle is an occasional pest of snap beans and soybeans throughout the southeastern U. S. Beetles are more likely to be active in places with a lot of soybean farms, but they can still find beans in garden plots that are spread out. Adult beetles chew round holes in the leaves of beans, peas, cowpeas, soybeans, corn and related weeds. They prefer young, tender tissue, and can kill seedlings and young plants when numerous. Older bean plants can handle some damage from feeding (15–30%) depending on their stage of development, but yields will drop if leaves fall off in large amounts. These beetles also leave rough spots on the pods, which makes the pods much less good and could be a way for fungal diseases to get in. If you’re growing beans to shell, the damage to the pods may not be too bad since it usually only affects the outside layers. The larvae feed on the roots, but really only do significant damage on seedling plants. Bugs that eat bean leaves are about 1/4 inch long and come in a range of colors, from red to yellowish-green to brown. There are four black spots on their backs, a black band around the edge of their wing covers, and a small black triangle behind their heads. They might not be easy to see on your bean plants because they feed on the underside of the leaves or where two leaves overlap to make a shelter. When disturbed, they tend to fall to the ground. As an adult, the bean leaf beetle spends the winter close to the ground, under leaves or other debris in or near bean plants. They emerge in mid-May to early June, and start to feed before mating. Females lay their small, orange eggs in small clusters around the base of the plants. They lay eggs that hatch in one to three weeks. The worm-like, whitish larvae eat the roots and underground stems for about 30 days before pupating in a cell made of dirt. The adults emerge about in about a week. Every year, there are two generations. The adults of the first generation show up in early summer, and the adults of the second generation show up in late August or early September. Controlling bean leaf beetle is not always easy. Planting beans later may reduce early season bean leaf beetle damage. If the adults have nothing to eat when they emerge, they may leave before your been seedlings emerge. However, adults may migrate in after the beans come up. Row covers can physically keep these bugs out, but they need to be put on before the beetles get to the plants. Foliar insecticides can get rid of bean leaf beetles, but they need to be spread over the whole plant, including the underside of the leaves. For advice on which products to use, talk to the Extension office in your county, and always read the label before using. – Susan Mahr, University of Wisconsin – Madison.
Green beans are a delicious vegetable that can be grown easily in home gardens. However, you may sometimes notice damage on the leaves, with small holes chewed into them. What sort of pests could be eating your green bean plants? Read on to learn how to identify the culprits and protect your crop.
Common Green Bean Leaf Pests
Several insects are attracted to the tender, juicy leaves of green bean plants. Here are some of the most likely suspects if you notice holes chewed into the foliage:
Bean Leaf Beetles
The bean leaf beetle is a very common pest of green beans. These small, oval beetles are typically yellowish to reddish-brown They chew small, round holes in leaves, which can add up to significant damage Bean leaf beetles can also feed directly on the developing bean pods.
Adult bean leaf beetles are most active in early summer and again in late summer through early fall. Controlling them through the growing season is key to preventing major defoliation.
Japanese Beetles
Japanese beetles are a highly destructive pest found throughout much of the US. As adults, these metallic green and copper beetles feed voraciously on the leaves, flowers, and pods of green beans and many other plants
Japanese beetles leave behind a characteristic lace-like skeletonization damage as they feed on the softer leaf tissue between veins. They are present during summer months.
Aphids
Several species of small, pear-shaped aphids or plant lice can infest green beans. They feed by sucking sap from the leaves and stems. Heavy aphid populations can stunt plants and cause curled, wrinkled leaves. Some species also excrete sticky honeydew that attracts sooty mold.
Aphids tend to cluster on the undersides of leaves and on new growth. Ants may also be present “farming” the aphids for their honeydew.
Thrips
These tiny insects have slender, fringed wings and feed by scraping and rasping leaf surfaces. Their feeding can produce silvery patches, flecks, or streaks on foliage. Thrips may also transmit some viral diseases among plants.
Thrips are most active in hot, dry conditions. Check the undersides of leaves for these tiny pests. Their feces may appear as small black dots on the leaves.
Spider Mites
Spider mites are not insects, but tiny 8-legged arachnids closely related to spiders. The twospotted spider mite is common on green beans. Their feeding removes chlorophyll, causing a stippling of light dots on the leaves.
Webbing may be visible upon close inspection in heavy mite infestations. Hot, dry weather promotes rapid spider mite reproduction.
Inspect Plants Frequently
To identify what insect or other pest may be damaging your green bean plants, inspect the foliage carefully at least once a week. Look on both upper and lower leaf surfaces for the culprits.
Pay particular attention to the undersides of leaves, as many pests like to hide and feed there. Webbing, honeydew, frass, and other signs can also point to the pest. Accurately identifying the problem is key for effective control.
Remove Heavily Infested Leaves
To quickly reduce pest populations, simply remove and destroy any heavily infested leaves. Check carefully and remove any insects, eggs, or larvae you find. This manual control can help slow pest damage.
Focus on removing leaves with large numbers of aphids, spider mites, bean leaf beetle larvae, or other immature pests before they can multiply further. But avoid excessively denuding the plants.
Apply Insecticidal Soaps
Insecticidal soaps are a safe, effective treatment against many soft-bodied pests like aphids, thrips, and spider mites. The soap disrupts cell membranes and causes insects to desiccate and die. Spray plants thoroughly, especially leaf undersides, about once a week or as needed.
Insecticidal soap will leave beneficial insects like lady beetles unaffected. Always follow label directions for proper dilution and application.
Employ Natural Predators
Encouraging natural predators like birds, lady beetles, lacewings, and predatory mites can reduce pest numbers. Avoid applying broad-spectrum insecticides which would kill populations of these beneficial insects.
Provide habitat like native plants and consider purchasing some predators. Lady beetles and lacewings can be ordered for release onto infested plants.
Apply Neem Oil
Neem oil is extracted from the tropical neem tree. It coats insects upon contact and interferes with their feeding, growth, and reproduction. Neem oil is environmentally friendly and safe for pollinators.
It is effective against many chewing and sucking pests including beetles, aphids, and mites. Apply neem oil spray once a week or more frequently if pests persist. Carefully coat the undersides of all leaves.
Use Row Covers
Floating row covers can exclude many larger pests like bean leaf beetles and Japanese beetles, preventing them from reaching plants. Cover plants with the fabric once they are 6-8 inches tall and secure the edges well.
Leave the covers on until flowering, then remove so pollinators can reach the blossoms. Replace afterwards if beetles persist. Ensure proper ventilation under the fabric.
Plant Resistant Varieties
Some green bean varieties have genetic resistance to certain insect pests and diseases. Choose resistant cultivars when available. For example, many bush beans have resistance to rust and mosaic viruses.
Ask your local nursery or extension office for recommended resistant varieties for your area. This is an easy, preventive way to avoid some pest problems.
Practice Good Garden Hygiene
Keep your garden free of weeds, debris, and infested plant residues which can harbor pests overwinter or allow them to spread. Dispose of heavily infested bean plants at the end of the season. Rotate bean crops to different garden areas in subsequent years.
Clean up fallen leaves, mulch, boards, or anything else pests could hide under. A clean garden removes protective habitat for many insects and mites.
Take an Integrated Approach
An integrated pest management (IPM) strategy combines multiple control methods for the most effective and sustainable results. Mechanical, biological, cultural, and lower toxicity chemical controls together can minimize damage while preserving beneficial insects.
Don’t rely on just one method alone. Utilize a combination of approaches tailored to the specific pests you have identified on your green bean plants. With diligent monitoring and timely intervention, you can enjoy a bountiful harvet!
k
Featured Articles by Season
Ask Your Gardening Question
If you’re unable to find the information you need, please submit your gardening question here:
Q&A – What is eating holes in my green bean leaves?
FAQ
How do I keep bugs from eating my green bean leaves?
What eats holes in green bean leaves?
How do you make bug spray for green beans?