Green beans are one of the simplest garden vegetables to grow, producing a bountiful crop with very little care. Most bean pests are easily controlled through natural means and rarely require the use of pesticides. Watch for the following pests in your bean patch:
Aphids are small, green, red or gray insects that are most prevalent during the early summer, but can appear anytime. They don’t eat holes in the leaves, but pierce leaves and stems, sucking the juices from the plants. Plants may droop or leaves may turn yellow during aphid infestations. You may also notice honeydew, a sticky substance secreted by aphids, on the leaves and soil. An increase in ant populations also indicates aphid infestations because the ants feed on honeydew. Look on the undersides of the leaves for the aphids themselves.
Aphids tend to appear cyclically so they’ll probably move on by themselves in a few weeks. Ladybugs, predatory wasps and lacewings prey on aphids and may keep populations under control without any help from you. If, however, the aphids are damaging your bean plants, spray them with a steady stream of water from the hose or apply insecticidal soap to the leaves, coating both the tops and bottoms well to cover the aphids.
Thrips, like aphids, are small, barely noticeable insects that suck the juices from bean plants. If they appear while beans are flowering, the beans may fail to pollinate or the resulting pods may be deformed. Lay aluminum foil on the soil after planting to repel thrips or treat them with insecticidal soap.
Mexican bean beetles look like large, brown ladybugs, and although they may appear early in the summer, they cause the most damage in mid-to-late summer. You may also notice Japanese beetles, which are shiny and green, or brown-spotted bean leaf beetles munching on your plants. These voracious insects usually feed on the undersides of the leaves, leaving the veins intact. Occasionally, beetles may also feed on pods and stems.
Outwit beetles by planting fast-growing varieties that mature before they appear. Hand-pick beetles off bean plants and drop them in a bucket of soapy water to destroy them. Watch for their yellow, fuzzy larva and yellow eggs, and destroy them, as well.
Corn earworms and cabbage loopers aren’t as picky about their diet as their names imply. Both insect pests eat beans, as well as corn and cabbage. These pests are most troublesome in late-planted crops and can quickly decimate an entire row of beans.
Spray the bean plants with Bacillus thuringiensis, also known as Bt, to control feeding caterpillars. Bt is a natural soil bacterium that paralyzes the gut of these insects, slowly starving them. The process takes three or four days, but the insects stop feeding almost immediately. Bt doesn’t damage bean plants and is safe for other animals and insects.
General Recommendations on Bean Plant Pests
Pest problems tend to vary from year to year, but good cultural practices can minimize their appearance and also ensure healthy bean plants that are more able to survive insect infestations. Till the soil in early spring if you’ve had problems with bean pests. Tilling will destroy any overwintering insects. Rotate bean crops from year to year to confuse and thwart bean pests.
Plant beans in full sun in late spring, two weeks after the last frost. Bean seeds do not tolerate cold, soggy soil and may be stunted or fail to appear altogether. Plant bean seeds 1 inch deep and 2 to 4 inches apart. Thin them so they stand 12 inches apart after true leaves emerge. Water them to keep the soil evenly moist, and monitor the garden often for insect pests.