Bean beetles, also commonly called Mexican bean beetles (Epilachna varivestis), closely resemble ladybugs, with their shape and spots. Their bronze bodies feature 16 black spots and measure about 1/4 inch. Bean beetle larvae are orange or yellow spiky-looking, fat, oval-shaped grubs that measure about 1/3 inch. Adult bean beetles usually nest in leaves and garden debris, where they spend their winters before emerging in late spring to lay eggs. These garden pests destroy leaves of affected bean plants, potentially damaging and killing plants. Organic pest control measures minimize damaging outbreaks without contaminating crops.
As Benjamin Franklin famously quipped, "An ounce of prevention is worth a pound of cure." Placing floating row covers over seedlings and young bean plants helps prevent bean beetles from laying eggs, preventing them from hatching and destroying crops later. Other easy ways to minimize infestations include planting resistant bean cultivars and planting beans as early as possible to harvest plants before July and August, peak times for bean beetle damage. It is also beneficial to remove foliage and debris after harvesting plants so bean beetles won't have places to nest for the winter.
According to the University of California, gardeners can use aluminum foil mulch to repel many insects, including bean beetles. The mulch works by reflecting the sun's ultraviolet rays, which discourages flying pests from landing on the bean plants. Before planting beans, remove any existing weeds. Cover the planting area with aluminum-coated construction paper, burying the edges of each sheet to hold the mulch in place. Cut a 3- to 6-inch diameter hole in the mulch, planting seeds or transplanted bean plants in the hole.
Interspersing bean plants with companion plants allows gardeners to take advantage of natural components in plants to either attract beneficial insects to the garden -- insects that destroy bean beetles -- or repel the pests, keeping them away from susceptible plants. Marigolds (Calendula) and rosemary (Rosmarinus officinalis) repel bean beetles. Try introducing parasitic wasps such as eulophid or pedio wasps to the garden. These natural enemies of insects such as aphids and bean beetles offer natural control measures. Select nectar-rich flowering plants such as daisies (Leucanthemum), sweet alyssum (Lobularia maritima) or yarrow (Achillea) to attract them.
Trap and Destroy
In small gardens, gardeners can hand-pick adult bean beetles and larvae off of plants, destroying the pests to prevent further infestation and additional generations. . Gardeners can also plant trap crops such as soybeans, destroying them after they become infested with bean beetle larvae.
Organic pest control measures may also include treating plants with neem oil, a natural and nontoxic substance that comes from the seeds of the neem tree. Neem oil is harmless to beneficial insects, humans and pets and does not require using protective equipment to apply. The National Gardening Association recommends applying neem oil to deter feeding bean beetle adults. An organic insecticidal soap may aid gardeners in controlling and destroying beetle larvae.
- National Gardening Association: Mexican Bean Beetle
- University of California: How You Can Grow Food Organically
- University of California Statewide Integrated Pest Management Program: Aluminum Foil Mulch
- Garden Toad: Companion Plant Guide
- Weekend Gardener: Bean Beetle Control
- I Grow Veg: Beneficial Bees and Parasitic Wasps in the Vegetable Garden
- University of Florida: Mexican Bean Beetle
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