There are numerous pests that can invade the vegetable garden and destroy the plants. Pesticides and insecticides have no place in an area that grows edibles due to the toxicity and danger associated with contact of such substances. Natural remedies have been used by farmers and home growers for years. The secret is companion planting. Many plants offer benefits to other plants and utilizing these properties makes a better and healthier garden.
Mexican Bean Beetle
Mexican bean beetles are native to Mexico but have spread to parts of the U.S., especially the Southwest. They arrive after overwintering in May to eat snap and lima beans, and then as the season progresses they infest soybean crops. The beetles resemble ladybugs, but are not beneficial like that insect. Instead, the adults and larva feed on bean leaves and cause wide spread defoliation. Insecticides are relatively ineffective on these pests.
Bean Leaf Beetle
Bean leaf beetles are crop-infesting pests that transmit a virus to bean plants. The bean pod mottle virus is a serious infection in soybean crops and has been known to decimate entire season yields. The best treatment is to destroy (as much as possible) the first generation of beetles. This will lessen the second generation's impact on the plants in the crucial growth stages of the late season.
Vegetables and herbs can be planted near each other to exploit a beneficial trait. This may be support, insect control and repellent, weed deterrence and providing shelter for beneficial predators. Many herbs contain oils or odors that repel certain types of pests, including insects. Sage is a good companion plant for beans and it also has insect-repelling properties, especially against beetles. Sage is a strong aromatic--it may be this that repels some insects.
Beetles on sage may not be bean beetles, but may actually be ladybugs. The Mexican bean beetle looks very similar and is, in fact, a relative. If companion planting has been done, the beans and sage will be next to each other. Any infestation on the beans will spill over to nearby plants. Sage does not repel all insects, so it would be a beetle which is resistant to the herb. Sage is a very hardy herb and it is unlikely the beetles will hurt the plant.
Beetles will primarily damage foliage, but can in the long term decrease crop yield. The best defense is a post-season offense. Clean up all old debris in the vegetable garden to get rid of eggs that beetles lay on plants. Plant rosemary where you will put your beans next season as this is also an effective beetle deterrent. If all else fails, you may have to consult your county extension or a university horticultural department for advice on safe pesticides for use around food.