Anthracnose in French beans

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By KELVIN THEURI

The rainy season this time has been an advantage to some farmers and a disadvantage to the others. The recent heavy downpour has had devastating effects since pesticides get washed off quickly and fungal diseases spread faster. The most dangerous fungal diseases in bean farming are rust and anthracnose. Whereas some farmers will be counting profits from the bountiful harvest, bean farmers in various regions will be counting losses since their fields have flooded and their crops attacked by anthracnose. In Ngobit, Mweiga, symptoms of anthracnose have already become visible.  The frequent heavy rains are increasing the occurrence and seriousness of the disease, and if not controlled, it will have devastating effects on French bean quality and production.

Anthracnose is a fungal disease that commonly attacks peppers, tomato, corn, cucumber, avocado, and French beans. In French beans, it spreads rapidly, especially when there is poor circulation of air, wet weather or high temperatures. It is spread by wind, rain splash, and mechanical contact. The fungal disease starts on older leaves appearing as small colored spots, but spreads to the stems, younger leaves and eventually to the pods. With time, the enlarge and become darker, the stem becomes weak and the leaves fall off. Eventually, the bean plants die.

Disease Cycle

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Prolonged periods of high humidity, cool and moderate temperatures, and water on young pods lead to the development of anthracnose. Moisture is required for the germination, development, and spread of spores and infection on the plant. Heavy rainfall results in prolonged wet conditions in the soil. This provides an ideal environment for fungus causing anthracnose to establish its infection. From infection, it takes from 5-10 days for the symptoms to be visible depending on the age of the tissues, bean variety, and temperature. The fungal spores can also be spread during transportation or when moving machinery through fields contaminated with anthracnose.

Prevention and Control

Cultural

Farmers should plant certified seeds that are anthracnose-free.

Cleaning stations in places that have been affected by anthracnose should be properly cleaned since they can be sources of contaminated dust.

Crop rotation provides root-rotting organisms that create an environment that the fungus cannot survive in.

Some bean varieties such as Goal Revolution (Boston), Samantha, Amy, and Teresa offer some resistance to anthracnose. Unfortunately, there are different races and forms of the fungus hence one variety may only be resistant to certain forms of the fungus.

The diseased plants should be removed to prevent the spread of anthracnose.

Avoid harvest french beans when wet to minimize the spread of fungal spores.

Chemical

Seeds should be treated to ensure that the seeds are anthracnose-free. If anthracnose is detected, the plants can be sprayed with chemicals such as Ducasse.

French beans are profitable crops if appropriate control measures are applied. The presence of anthracnose on the french beans results in rejection of the product which can be a huge loss to the farmer. However, farmers should only use the allowed pesticides at the recommended rates.

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