Beans

Bean beetle control in Mexico: preventing bean beetles from invading plants

Ladybugs are a gardener’s best friends, they eat aphids and generally brighten up the place. Although most members of the Coccinellidae family are useful allies in the garden, the Mexican bean leaf beetle ( Epilachna varivestis ) can be devastating to plants. Read on for information on how to control the Mexican bean leaf beetle to prevent damage from this insect in your garden.

Facts about the Mexican bean beetle

Mexican bean beetles are found throughout the United States east of the Rocky Mountains, but are thought to be native to Mexico. These beetles thrive in areas where summers are humid or in agricultural areas where heavy irrigation is required. The red-orange spotted adults emerge in mid-summer in search of lime, broom and soybean plantations, where they lay their eggs in groups of 40-75 on the underside of leaves.

Bean beetle damage

Adults and larvae of the Mexican beetle feed on the foliage of beans, chewing the soft tissue between the veins on the underside of the leaf. The upper surfaces may turn yellow and areas where the tissue has been chewed into a very thin layer may dry out and fall off, leaving holes in the leaves. When feeding pressure is high, leaves fall off and plants may die. Large populations of bean beetles spread from the leaves to attack flowers and pods as their numbers increase.

Control of the Mexican Bean Beetle

A gardener confronted with heavily attacked beans may wonder if it is possible to control bean beetles, but there are several options suitable for each type of garden. Organic gardeners wondering how to keep beetles away from plants have options such as floating row covers, installed before the beetles arrive in the area. Although row covers can be cumbersome during harvest, they prevent the beetles from settling in the beans.

Selecting early bean varieties with shrubby habits allows you to grow many beans before the Mexican beetles have begun to emerge from their winter rest. By the time the insects are looking for places to feed, your beans will have been harvested. If you plough the exhausted plants immediately, you will help reduce the number of bean beetles by depriving them of food.

Insecticides often seem to fail because bean beetles migrate throughout the season, resulting in continuous waves of new pests despite treatments. If you decide to use insecticides, be sure to re-spray your beans before the residual effects of the previous poison application wear off; otherwise, the next immigration of bean leaf beetle may destroy your beans. Labelled pesticides include acephate, acetamiprid, carbaryl, dimethoate, disulfoton, endosulfan, esfenvalerate, gamma-cyhalothrin, lambda-cyhalothrin, malathion, methomyl and zeta-cyhalothrin.

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