Bean Pests

It sounds as though you're dealing with an infestation of Mexican bean beetles. Adults are round beetles with 16 black spots on their wings, and can be mistaken for orange colored ladybugs. They can be formidable foes. Inspect plants frequently; handpick adult beetles from the plants and squish their yellow-orange eggs (found on the undersides of leaves). You may be able to manage the pest population at acceptable level simply by interplanting beans with garlic, nasturtiums, marigolds, or potatoes, which help repel the beetles.

Be sure to clean up bean plant debris right after harvest so adults won't have a place to hide. Plant beans early to avoid attack, and try growing a variety of plants to attract predacious wasps and assassin bugs, both of which eat Mexican bean beetles. Since beans are self-pollinating, you can cover the plants with fabric row cover to create a barrier agains the beetles.

As a last resort, spray plants weekly with an organic pesticide such as neem. Make sure to spray the undersides of leaves as well.

Blight on Pole Beans

Those are classic symptoms of a common bacterial disease called halo blight. This disease thrives in high humidity with temperatures in the low 70s. It's mostly a problem east of the Rocky Mountains and is spread primarily by infected seed or plant debris left on the soil. Infection usually begins with small, brown, angular, water-soaked spots on the lower leaves. The spots later expand and the leaves turn yellow, sometimes producing the characteristic halos around the spots. The disease can eventually defoliate the plant and infect the bean pods. If you notice the disease on young plants, pull them up, destroy them and replant. Consider growing less-susceptible varieties such as Blue Lake. If the plants are already producing beans when the disease strikes, harvest what you can, then destroy the plants as soon as production begins to decline. In the future, try the following preventive steps. Buy disease-free seed from a reputable company. Plant beans in the same ground only once every three years. Choose a spot where they'll get morning sun so foliage dries quickly. Use a wider spacing between plants for air circulation. And don't work in the bean patch when it's wet.