Spotted Beans: Reasons for brown spots on beans

Beans are one of the easiest crops to grow in the garden, so even the most novice gardener feels massive success when his beans germinate an unexpected pod clump. Unfortunately, some spotted beans appear in the garden every year, especially when the weather has been wet. Brown spots on beans are often caused by bacterial or fungal diseases, but don’t worry, you can save them.

Diseases of bean plants with brown spot

Brown spots on beans are a common symptom of bean disease, and many occur even under the same conditions, making it difficult to tell if a fungal or bacterial disease is your problem. However, if you look closely, you can distinguish bacterial from fungal spots, making treatment easier.

• Bean anthracnose causes large brown spots to appear on the bean leaves, with more severe damage near the soil line. It can spread rapidly, consuming the entire plant if left untreated. When beans infected with anthracnose are harvested and brought indoors, they quickly develop white fungal bodies on their surface.
• Bacterial brown spot begins as small water-soaked spots on the foliage, but spreads rapidly to dead areas surrounded by a yellow margin. Sometimes these spots develop inside each other or dead material falls from the leaf, giving it a worn appearance. The spots on the pods are brown and sunken, and the young pods emerge twisted or bent.
• Fire blight is a bacterial disease similar in appearance to bacterial brown spot, but water-soaked lesions also appear on bean pods. They grow rapidly in rusty areas and, under moist conditions, may ooze a yellow liquid. Seed abortion or discoloration is not uncommon.
• Halo blight can be distinguished from other bacterial parasites by the red-orange leaf spots surrounded by green-yellow halos of varying sizes. The spots almost completely disappear when temperatures exceed 80 degrees Fahrenheit. These lesions may ooze cream-coloured liquid when the weather is humid.

Treatment of stains on beans

Spotted beans are generally not a source of fear; they require immediate treatment, but with a quick response, you can save most or all of your crop. It is helpful to determine if the spots you see are caused by a fungus or a bacterium so you can choose a chemical that targets that organism.

Treat fungal infections with neem oil, applied every 10 days for several weeks. Bacterial diseases are more likely to respond to a copper-based fungicide, but several treatments may be necessary to produce a suitable crop. In the future, be sure to move away from the bean plot when the foliage is wet to reduce the risk of spreading these diseases. Keep bean leaves and other wastes off the ground, as these dead tissues can harbour pathogens.