Black, sunken, oozing spots on your beans? Could be the fungus colletorichum lindemuthianumotherwise known as bean anthrachose. Find out what it is and what to do.
What is it?
The fungus colletotrichum lindemuthianum causes this plant disease. Although it strikes all varieties of beans, it is most damaging to lima bean varieties. This fungus thrives in cool, wet weather conditions.
What does it look like?
Brown specks and dots appear on pods and become sunken over time. Circular spots, which ooze a salmon-colored liquid as the fungus spreads will also appear on various areas of the bean plants. Elongated reddish brown spots may also show up on infected stems, leaves and seedlings. Once this occurs seedlings quickly die.
How does it manifest?
Animals, people, tools, splashing water and other such contact carry spores to healthy bean plants from damaged ones. The fungi also thrive on diseased bean seeds which when stored and planted cause plants to have stunted and diseased growth. Plant debris left over in the garden can also harbor the fungus and serve as a thriving breeding ground.
What can you do about it?
When you first notice damage on bean plants, remove and destroy all diseased plants to avoid further infection from contact. As soon as beans begin to flower, apply chlorothalonil containing fungicide for a total of three treatments at 10 day intervals. Avoid working in the garden when plants are wet to avoid spread by contact and accidental splashing of water. Avoid initial occurrence and damage by buying reputable seeds from a well-respected nursery or garden center. Once an area has been infected with colletotrichum lindemuthianum , reinfections can occur for up to 3 years, so it is best to plant beans in a new site each year.