---

The first insect question I had this spring was about something eating their bean leaves. The invader wasn't eating the whole leaf as a deer would do, but rather small holes in the leaves. There are several insects that attack beans and one of them is the bean leaf beetle.

According to the Department of Entomology, U of M, due to the late planting this spring, there should be fewer of them this year. The insects were there but because the beans were planted later than usual, the leaf beetle chose to feast on other legumes. The adult is about 1/4 inch long with a range of colors from red to greenish yellow and have black spots with a black triangle just behind the head. Some bean leaf beetles have spots and some don't but all have that black triangle where their wings come together.

It overwinters in the adult form in the soil under leaves, and surfaces in late spring to feed. They lay clusters of about a dozen orange eggs in the soil under host plants. The larvae are bluish white grubs, about an inch long and fairly narrow. These beetle larvae bore into the roots and nodules of many legumes.

Adults feed in mid-July to September on the undersides of leaves, and make large round holes. Adults also feed on the pods and can make openings where diseases can enter. They spread a number of virus diseases to host plants which cause yellowing of the leaves and stunted growth.

Another insect that is destructive to beans is the Mexican bean beetle. It looks almost identical to the ladybug, but has no white markings between the head and body, as the ladybug does. It is 1/3 of an inch long and mustard brown in color with black spots. It lays clusters of 40 to 60 lemon yellow eggs on the undersides of bean leaves. If you see single (not clustered) eggs that are pale orange and opaque, leave them alone. They probably belong to the beneficial aphid-eating ladybug.

The Mexican bean beetles attack beans, cabbage, kale, collard, and mustard greens. While the bean leaf beetle eats round holes on the leaf, the Mexican bean beetle skeletonizes the leaf leaving only the veins of the leaf. The one advantage is that it takes much longer for the Mexican beetle to defoliate the bean, thus it takes longer to seriously affect the yield.

Plant pathologist Katharine Widin, has some tips on controlling bean insects. Garden cleanup in the fall is one of the best methods for disrupting insect life cycles and preventing overwintering in or near the garden. Tilling after cleanup also exposes insects in the soil to drying, freezing, and predators.

Simple soap sprays and other home remedies may help deter pests. Handpicking, using resistant varieties, annual crop rotation, as well as good garden clean up should keep insects under control.

---