Bean Mosaic

If you planted beans, you may notice a problem with leaves looking pale, splotchy, and generally unhealthy. Blotchy, puckered bean leaves may indicate a bean mosaic virus.

Bean leaf mosaic (Scot Nelson) Public Domain

Several mosaic viruses attack beans. Here are the three most common ones:

• Bean common mosaic cost farmers 80% of their crop when it first arrived in the US in 1917, and it is seed-borne, meaning it can get on your property through seeds from the grocery store.
• Bean yellow mosaic overwinters in clover, gladiolus, and wild legumes; not seed-borne.
• Cucumber mosaic is seed borne; overwinters in weeds.

Symptoms of bean mosaic

Bean mosaic symptoms vary between types of beans, life stages, and specific viruses, but you will want to keep a lookout for these symptoms in your bean patch:

• Infected leaves may be mottled green or yellow.
• Bands may be visible in some plant veins.
• Leaf chlorosis between the veins may occur.
• Distorted, cupped, wrinkled, or downward curling leaves.

Vectors of infection

Bean mosaic is spread by sap-sucking insects such as aphids, mealybugs, and leafhoppers. While it sounds convenient, research has shown that using insecticides is not practical because it kills the beneficial insects that feed on the pests. Once a plant is infected, remove it because it is a vector for disease. Do not add infected plants to the compost pile.

Controlling bean mosaic

Prevention is the best protection when it comes to bean mosaic. Use these handy tips to reduce the likelihood of future generations of beans becoming infected:

• Remove nearby broadleaf weeds. The weeds may provide a habitat for the virus and the vector insects that carry it to your plants.
• Installing reflective mulch may repel insects. You can buy rolls of silver polyethylene from a garden store, paint some cardboard with silver paint, or lay aluminum foil around your plants for the same results. Just be sure to remove reflective mulch before temperatures get hot, or it can cook your plants!
• Buy disease-free seeds from reputable suppliers.
• Buy resistant varieties (heirlooms are less likely to have this characteristic).
• Do not plant beans near clover, alfalfa, rye, or other legumes.
• Rotate bean crops each year.
• Start plants early enough in the season that they reach the flowering stage before aphids become a problem.
• Treat heavy aphid infestations with neem oil or insecticidal soap.

Bean mosaic is one of the reasons you should not use dried beans from the grocery store to plant in your garden. While they are perfectly safe to eat, there is no guarantee they are safe to sow. Invest in high-quality, guaranteed clean seeds from a reputable seller, and then save the best pods from your crop for replanting.

Beans are easy to grow. They improve soil structure, provide excellent food crops, and can look lovely in a landscape.