Bean Diseases

Generally, beans are an easy vegetable to grow in the home garden. There are however, many pests and diseases which can cause problems resulting in failed crops.

All of these can be remedied by regular walks through the garden to check plants for signs of disease and pests. A list of diseases, the damage they cause and tips for saving plants can be seen below.

Bacterial Blight

Brown-spot blight is a fungal disease which can be found on Lima beans. Reddish-brown spots appear on leaves sometimes surrounded by lighter green rings. Leaves become dry and brittle dropping from the plant.

Remove and destroy affected plants. Using a plant dust containing copper and sulfur is an effective way to control fungal diseases. These can be found at organic garden supply shops or in garden supply catalogs. Serenade® Garden Disease Control Spray works well to control blights and mildews.

Bean Mosaic

Bean mosaic is a viral disease spread by aphids from plant to plant. Leaves of infected plants will be crinkled and mottled with yellow coloring. Leaves may also curve downward. Seeds will be small and wrinkled or shriveled. Plants will not grow well and therefore, will be stunted.

Infected plants should be removed and destroyed. Preventative measures should be taken early on by controlling aphids.

Calcium Deficiency

Plants are stunted, tips of stems may turn black and die and edges of leaves turn yellow and curl.

Test soil pH level. If it is below 6.2, add calcitic lime to bring pH level to between 6.0 and 7.0. Soil should be kept evenly moist, never the extreme; too wet or too dry.

Curly Top Virus

Curly top is another viral disease which causes leaves to curl downward and plant to be severely stunted.

Infected plants should be removed and destroyed. Aphids transfer this virus so controlling aphids through the seasons will help control or eliminate this disease.

Downy Mildew

Downy mildew, powdery mildew and white mold are fungal diseases. Fungal disease thrives where the weather is warm and damp. Downy mildew is a problem for lima beans causing white patches on new plant growth and flowers of the plant. The veins of leaves become twisted and turn a reddish-purple color. Powdery mildew and white mold affect all types of beans causing a white fuzzy powder on plant leaves similar to but larger than downy mildew.

Spraying plants with sulfur specifically formulated to control fungal plant disease is best done before signs are evident or at the very latest, at first signs of infection. *See Bacterial Blight above for more control measures.

Nitrogen Deficiency

Signs plants show when lacking nitrogen are stunted growth and yellow and dropping leaves.

It is best to prevent this deficiency by adding a well-balanced compost mixture to the soil before planting. To treat plants with nitrogen deficiency, use fish emulsion on foliage and roots.

Root Rot

Another fungal disease, root rot causes seedlings to die or not come up at all. Plants infected will be severely stunted and yellowing. Roots of plants with root rot have reddish-black streaks. Wet soil accompanied by cool weather provides conditions perfect for root rot to spread.

Eliminate infected plants by pulling them out and destroying them. Planting new seed in warm, well-draining soil should be all that is needed to grow plants without root rot.

Zinc Deficiency

Plants lacking in zinc may bloom but not form fruit. If fruit, in this case bean pods, do form they will drop from plant.

Fertilize plants with liquid seaweed fertilizer to prevent this problem.

Extreme Temperatures

Heat

In very hot areas extreme heat will cause flower drop and plants will not produce beans. If temperature climbs above 85°-90° F. for several days in a row, a little shade from row covers can be provided.

Cold

Beans like to grow where it is warm. If temperatures are expected to fall below 45° F, cover plants with row covers to protect them from cold winds.

Final Tips

It is always best to do everything humanly possible to prevent disease rather than treat it. To accomplish this:

• Plant seeds in healthy, composted, well-drained soil.
• Rotate bean crops every two to three years.
• Be sure to never over or under water plants.
• Check regularly for signs of unhealthy plants.

For a list of heirloom beans that are making a come-back in gardens today, see the article ‚”Heirloom Beans of Note.”