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Bean Beetles and other Bean Pests

Bean Leaf Beetle Bean Leaf Beetle
There is a whole array of insect pests who live to eat your bean plants. They attack quickly and can make a defoliated mess of your plants if left unchecked. Luckily, it is possible to mount an organic defense against them. Here are the keys to protecting the bean citizens of your garden kingdom:

  1. Identify which pests are attacking your beans

  2. Learn what organic controls exist for the pests that are plaguing you

  3. Use your control strategies as early in the growing season as you can, before the bean-eating insect troops have mounted a full scale invasion in your garden.

Many of the pests devouring your beans are likely to be beetles. Mexican bean beetles, bean leaf beetles and both striped and spotted cucumber beetles love to feast on bean plants. Other bean-eating insects include cowpea curculios, cutworms, bean weevils, leaffooted bugs, leafhoppers and stinkbugs.

Some of these pests, such as the bean weevil, spread to your garden on infected seed. Others, such as the Mexican Bean Beetle, travel to your garden from nearby bean, alfalfa. corn or clover fields. No matter how these pests get into your garden, once they've moved in, they won't want to leave. Because many of these pests spawn several generations of offspring per year, your best bet to keep from being overrun with them is to keep their populations in check. Your bean plants can tolerate some insect nibbling but can't survive a full-on attack.


Who's the Bean Eater in My Garden?

Mexican Bean Beetle -- common in all parts of the US except the Pacific coast, 1/3'' long, wing covers have 8 black spots, lay their orange eggs on the underside of leaves in clusters of 40 or more (be sure that the eggs belong to Bean Beetles, not ladybugs which are their close cousins)

Bean Leaf Beetle -- prevalent in the Southeastern and Midwest US, lay their eggs in the soil, 1/4'' long, may or may not have spots, drop to the ground when disturbed

Striped Cucumber Beetle -- 1/4''long, yellowish green with 3 black stripes

Spotted Cucumber Beetle (AKA Southern corn rootworm) -- 1/4'' long, yellowish green with 12 spots on its back.

Cowpea curculio -- adults are shiny, black and 1/4'' long. Larvae are yellow maggots that are often found in the bean pods. Most common in the Southeastern US.

Bean Cutworm -- common in Western and Midwestern US. The cutworms are tan with a darker, faint diamond shaped pattern on their backs.

Bean Weevil -- dark grayish-brown, with grayish yellow hairs and dark bands across back. 1/10 '' long and has six reddish-brown legs.

Leaffooted bug and Stinkbugs -- shield-shaped 1/2-3/4'' long. Can be green or brown and may have stripes.

I know who the trouble maker is. How do I get rid of him?

Now that you know what's causing your problem, what's an effective, organic way to get rid of it or to help your plants cope with the onslaught? Part of the answer is that keeping your garden tidy by removing weeds, tall grasses and crop residues in and around it will eliminate some breeding sites for pests. Many of these pests have natural predators which will feed on them, thus reducing their numbers. Specific management practices such as matching planting dates with seasonal low points in pest populations or by using row covers to keep pests can help too.

Here's some information that will help you thwart the pests that are bugging you!

Mexican Bean Beetle -- The Pediobius wasp is a natural predator of Mexican Bean Beetle larvae.

Bean Leaf Beetle -- A floating row cover can be used to keep these pests away from young plants. Bean Leaf Beetles can be hand-picked off plants if you have a small garden. Mid-afternoon is often the best time to do so.

Cucumber Beetle--Natural predators include soldier beetles, tachinid flies and braconid wasps. Planting your beans later in the season when they will germinate and establish more quickly can help you fight this bad bug.

Cowpea curculio -- Natural predators include tachinid flies and ants. Keeping late-season plantings away from the sites of earlier plantings will keep the cowpea curculio's population from snowballing as the season wears on.

Bean Cutworm -- try using Bt to control this caterpillar.

Bean weevil -- heat treat seeds that you suspect are infected or buy seeds that you know are weevil free.

Leaffooted and stink bugs -- populations of these pests are highest in late summer to early fall. Work around their schedule by growing early crops. Take away their home and breeding sites by keeping weeds under control. Some common species of birds feed on stinkbugs.

Now you know more about these bean-eating pests and how to defeat them. Be persistent and you will have victory (and green beans for dinner!).


For further reading
Pictures of assorted bean pests


See Also:
There's a Goosefoot in my Garden
It's Easy to Grow Great Garlic
How Does Your Garden Grow Part One: Getting to Know Your Soil
Bountiful Basil

Digg! digg it

Tammy Biondi has been growing organic produce for over 10 years. Besides running Blue Horizon Farm, Tammy teaches about sustainable farming at the Central Carolina Community College. She also is a successful freelance writer, focusing on agricultural topics. Contact her at tammy@bluehorizonfarm.com.