If the leaves of your bean plants are looking lacy, Mexican bean beetles are at work.
This insect can weaken a plant to the point where it only produces a few beans or even dies. You could control the beetles by picking them off by hand, but sometimes they multiply and eat too fast.
If only it were 150 years ago, we wouldn't have to give bean beetles a second thought. The pest was unknown outside Mexico until the middle of the 19th century, when it started moving northward, possibly with the movement of food for cavalry during the Mexican War. By the 1880s, the beetles had reached Canada.
The Mexican bean beetle is now well-established throughout the United States. The beetles resemble ladybugs, but are tan with eight dark spots on their backs. The bright yellow, pill-shaped, spiny larvae are the ones doing most of the damage early in the season.
One way to prevent damage from bean beetles is with successive sowings of bush beans, each planting destroyed after being harvested but before the beetle larvae mature.
Another possibility is to spray the bean plants with insecticides such as rotenone, pyrethrin or sabadilla.
However, the spraying would have to be constant and thorough (the beetles and larvae feed on the undersides of the leaves), not an appealing thought when you're harvesting and eating a vegetable.
There are additional ways to keep this pest in check. Thorough cleanup of garden debris at the end of the season makes it harder for the adults to find a place to spend the winter. Unfortunately, the adults can overwinter in nearby woods, preferably oak or pine.
What you plant also may influence the severity of an infestation. Bean beetles are supposedly repelled from beans interplanted with potatoes and certain pole bean varieties such as Wade, Logan and Supergreen are somewhat resistant to beetles.
Another approach is to bring in an "army" to attack the Mexican bean beetles. Ladybugs, lacewings and nematodes all love to dine on bean beetles. Create a hospitable environment for this army by avoiding pesticide use.
These beneficial insects are found naturally; if necessary, increase their ranks by buying them.
They are available from Natural Insect Control (985) 382-2904 and GardensAlive (812) 537-8650.
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