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 summer crop that are easy to grow in home gardens. However, your precious bean plants can fall victim to various insect pests that feed on the leaves. Knowing what bugs are munching on your green beans is key to protecting your harvest.
In this article, we’ll go over the most common insects that attack green bean foliage so you can identify the culprits in your garden. We’ll also provide tips on how to control bean leaf-eating pests naturally and prevent damage.
The Bean Leaf Beetle
The most widespread and destructive pest of green bean leaves is the bean leaf beetle (Cerotoma trifurcata). This 1⁄4 inch long beetle varies in color from yellow to greenish-gray with four black spots on its wings.
Both the adult beetles and larvae feed voraciously on bean leaves, chewing out round holes and sometimes skeletonizing the foliage. Bean leaf beetles can also feed on developing bean pods, leaving scars and allowing diseases to enter.
If bean leaf beetle damage is severe, plants can become stressed and have reduced yields. So it’s important to control this pest before populations explode in midsummer. Handpicking beetles using row covers or applying neem oil can help reduce bean leaf beetle destruction.
Leafhoppers
Various species of tiny wedge-shaped insects called leafhoppers often take up residence in the bean patch. The most common ones that feed on bean leaves are potato leafhoppers spotted cucumber beetles, and aster leafhoppers.
Leafhoppers pierce plant tissues with their mouthparts and suck out the sap. This can cause yellow stippling, browning of leaf edges, and curling of leaves. A heavy infestation can even kill bean plants.
To deter leafhoppers, clear out weeds around the garden that serve as their breeding grounds. Floating row covers and sticky traps can also help exclude or capture them. Insecticidal soaps and neem oil applications may provide some control for severe infestations.
Cutworms
Plump, smooth-skinned caterpillars called cutworms are the larvae of various noctuid moth species. These night-feeding pests hide in soil by day and emerge at night to feast on bean plants.
Cutworms chew through bean stems at ground level, killing seedlings and young transplants. They also climb up plants to devour leaves. Look for ragged holes chewed in foliage as evidence of cutworms.
Protect bean plants with collars placed around stems at planting time. Beneficial nematodes applied to soil kill cutworms naturally. Or use Bacillus thuringiensis (Bt) spray on foliage to target cutworm caterpillars.
Blister Beetles
You may spot elongated black or gray beetles clustered on your bean plants – these are blister beetles. Attracted by bean flowers, blister beetles feed on leaves, flowers, and developing pods.
Besides damaging bean foliage and fruit, blister beetles also pose a health risk. Their bodies contain a chemical called cantharidin that causes painful blisters if touched. So wear gloves when handling these beetles if found in your garden.
Pick off any blister beetles you see on plants. You can also deter these pests by planting beans away from potato or tomato fields, which blister beetles prefer. Kaolin clay sprayed on plants acts as a repellent.
Mexican Bean Beetles
Mexican bean beetles (Epilachna varivestis) are copper-colored lady beetles with 16 black spots on their backs. Both adults and spiky-looking larvae feed on bean leaves and pods.
The bean beetles skeletonize the undersides of leaves, leaving only a thin layer of tissue behind. Heavily damaged leaves turn yellow, wither, and drop off. Mexican bean beetles can seriously reduce yields if not controlled.
Handpick adults and crush egg clusters early in spring to prevent infestations. Insecticidal soap and neem oil can deter the beetles but must be applied frequently once populations are high.
Spider Mites
Tiny red or yellow spider mites are closely related to spiders. The most common mite pest of beans is the two-spotted spider mite.
Spider mites suck sap from the undersides of leaves, causing a stippled, yellowed appearance. Webbing may be visible on heavily infested plants. Spider mites thrive in hot, dry conditions.
Blast plants with water to dislodge mites. Apply insecticidal soap every 5-7 days for 2 weeks to kill mites. Introduce predatory mites or ladybugs to devour pest mites.
Aphids
Several species of aphids can infest bean plants, including green peach aphids, bean aphids, and potato aphids. These tiny, soft-bodied insects gather on new growth and undersides of leaves to pierce tissues and feed on sap.
Large aphid populations cause curled, stunted, and yellowed leaves through their feeding. Honeydew secretions also promote growth of sooty mold fungus. Luckily, aphids have many natural predators that keep them in check.
Spray plants with a strong stream of water to knock off aphids. Apply horticultural oils or insecticidal soaps to smother them. Lady beetles, lacewings, and other beneficial insects will also help control aphids.
Flea Beetles
Tiny, jumping flea beetles chew numerous small holes in bean leaves, giving foliage a shotholed appearance. Pest species include the potato flea beetle and the pale-striped flea beetle.
Heavy feeding damage from flea beetles can reduce plant vigor and yield. The beetles also spread diseases like Stewart’s wilt. Use floating row cover to exclude flea beetles from plants when possible.
Neem oil and pyrethrins can provide some control of flea beetle populations. Diatomaceous earth sprinkled around plants deters the pests. Trap crops like radish or mustard planted around beans lure flea beetles away as well.
Slugs & Snails
Plump slugs and snails seem to take especial delight in munching the succulent leaves of bean plants. These slippery pests feed at night and hide under mulch and debris by day.
Look for large holes chewed in leaves as well as slime trails on foliage or the ground as evidence of their damage. Heavy feeding can quickly defoliate plants.
Prevent slug and snail damage by removing hiding spots from the garden. Spread diatomaceous earth around plants to shred the mollusks. Set out beer traps at night to attract and drown them.
Stink Bugs
Shiny shield or “stink” bugs such as brown marmorated, green, and brown stink bugs insert their needle-like mouthparts into bean pods and seeds to feed. This damages developing beans and can cause harvest losses.
Stink bugs also feed on bean leaves, causing yellow spotting and wilting. Their defensive odor makes them unappealing to predators. Exclude stink bugs with tight-fitting row covers over plants. Trap crops and pheromone traps can also help control populations.
Japanese Beetles
Metallic green and copper beetles that flock to feed on many plants, including beans, are Japanese beetles. As adults, these pests skeletonize leaves by devouring tissue between the veins and leaving a lace-like appearance.
Japanese beetles are difficult to control once established due to their widespread feeding on ornamentals and turfgrass. Handpick adults from plants in the morning when sluggish. Or spray neem oil, pyrethrins, or microbial controls to reduce damage.
Budworms & Earwigs
Caterpillars of corn earworm moths, also known as budworms or bollworms, attack bean pods as well as corn. Chewing damage causes pods to rot. Meanwhile, pinchers on the rear ends of dark earwigs allow them to snip holes in bean leaves at night.
Monitor plants for caterpillars and handpick them off plants. Use pheromone traps to capture adult moths. Diatomaceous earth and insecticidal soap deter earwigs. Keep garden areas clean of debris where insects hide.
Armyworms
Armyworm caterpillars eat not only corn but also bean leaves. Young worms chew ragged notches in leaf margins before progressing to shred foliage entirely as they mature. Heavy infestations can strip bean plants bare.
Apply Bacillus thuringiensis (Bt) at the first signs of caterpillars. Beneficial nematodes control armyworms biologically. Trap crop plants like buckwheat also divert the pests away from beans.
By learning to identify the bugs that commonly feed on green bean leaves, you can catch problems early before significant defoliation and plant damage occurs. Protect your bean crop with row covers, natural repellents, beneficial insects, and other organic controls. Let your beans thrive all summer long with fewer chewe
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