Crop Cleanup Trick
If you are bothered with Mexican bean beetles for more than one year in a row try the cleanup trick. Immediately pull up snap beans or lima beans as soon as they finish bearing their main crop and stuff the vines into a clear plastic trashbag. It is important that you don't wait till the very last bean has been picked. Pull those plants when the main harvest is over and the plants still have a population of the pest beetles. After tying the bag, leave it in the sun for a week or so. Nothing will survive that treatment and you will have disposed of the major source of next year's beetle population.
Early Planting Strategy
In the North,beetles tend to be more active in midsummer, so you can try planting your biggest crop as early in the season as your weather allows. This works only for bush beans since the pole beans take longer to mature. In general, earlier crops in the North are less troubled than later crops.
Find The Right Variety Of Bean
Beans are vegetable that come in many different varieties. What is important to note however is that all varieties of bean do not grow equally well or happily in all regions of the country. In other words, there are varieties of each type of bean that are best for your particular back yard and if you find them your problems with Mexican bean beetles go way down to almost nothing. This has nothing to do with “resitant” varieties. It has everything to do with the fact that a plant that is totally healthy and vigorous is seldom bothered by any insect pest, much less the Mexican bean beetle. So if you have annual visits from Mexican bean beetles we recommend you start growing some other varieties.
Keep Those Predators Happy
As with all the other pest insects that ever turn up as a problem in your landscape, the Mexican bean beetle has lots of critters just waiting to snack on bean beetles. Many of the most common songbirds eat Mexican bean beetles, as do toads if you have any of them in the yard. By feeding those birds all year round, you insure their presence when the bean beetle shows up.
All kinds of beneficial insects are bean beetle chompers including various parasitic wasps,assassin bugs anchor bugs big-eyed bugs, centipedes, pirate bugs, spined soldier beetles, spiders, ants, and tachinid flies just to name a few. Since any broad spectrum insecticide will kill any of these good guys, you should use that tool only as a last resort and only in limited areas of your yard and garden.