I noticed that the leaves of my bush beans were suffering a bit, but I chalked it up to some sudden extreme heat and dryness that we experienced last week. Oh, no. I was so wrong. The fiesta was well underway in a very covert manner. When I picked beans a few days ago, I seemed to have missed the early party goers, but this morning, they were in full view with their brightly colored party wear.
Attack of the Mexican Bean Beetle
If you grow beans, then you will eventually become acquainted with the Mexican bean beetle. The colorful, voracious larvae of this beetle will devour your bean plants. The adults look very much like the beneficial ladybugs. In fact, they are in the same family (Coccinellidae), but just like most families, two of its members have gone to the dark side. These are the squash lady beetle and the Mexican bean beetle. Unlike their carnivorous cousins, the squash lady beetle and the Mexican bean beetle attack plants.
The Mexican bean beetle (Epilachna varivestis) is thought to be native to southern Mexico. It can be found in nearly every state east of the Rockies and in the southwest region of the United States.
Adults emerge from their winter hiding spots in late spring, early summer. The adults look like a ladybug but are usually a dark orange to coppery color with 16 black spots. The females eat on bean plants for a short time before laying clusters of yellow eggs on the undersides of the leaves. A single female can lay as many as 500-600 eggs in her life time, usually in batches of 40-75 eggs.
The larvae hatch and begin their feasting on the leaves of the bean plants. As the larvae grow, they will shed their skin 4-5 times. So when you look for these guys, look for very small to larger sizes. I didn’t notice the larvae until they were much larger.
The larvae will then attach themselves to the underside of a leaf to pupate. Once the adults emerge, the cycle begins again.
To prevent the fiesta in the first place, floating row covers can be used to prevent females from laying their eggs. If, however, you fail on the row cover front, then get ready to hand pick the adults and larvae off your plants. If you are opposed to squishing (like me), take a cup of water with you to the garden that has a drop or two of dish washing liquid in it. Pick off the larvae and drop them in the cup. (Tell them you are sorry.) There are a few natural predators, but don’t count on them to find the party before your bean plants are destroyed.
If you think that your plants are too far gone or there is a very large infestation, pull your bean plants up by the roots and place the plants in a garbage bag. Secure the end and leave the bag of plants in the sun for a week or two before adding them to the compost pile. This will assure that the adults, larvae, and eggs do not survive.
And then…you start all over!