Bean Anthracnose is a seed-borne disease caused by the fungus Colletotrichum lindemuthianum. The disease is most common and severe on dry and snap beans but may also affect runner bean, mung bean, cowpea, and broad bean. Marketing losses are attributed to seed spots and blemishes, which lower their quality rating and salability.
Bean Anthracnose Cycle
The fungus can survive on contaminated seed and on crop debris for at least two years. This greatly depends on environmental conditions. Survival is drastically reduced, however, when infected materials are buried in the field and come in contact with water. Alternating wet-dry cycles in soil reduce survival of the fungus.
Cool to moderate temperatures and prolonged periods of high humidity or free water on the foliage and young pods promote bean anthracnose development. Moisture is required for development, spread, and germination of the spores as well as for infection of the plant. A prolonged wet period is necessary for the fungus to establish its infection.
The time from infection to visible symptoms ranges from 4 – 9 days, depending on the temperature, bean variety, and age of the tissues.
The fungal spores are easily carried to healthy plants in wind-blown rain, by people and machinery moving through contaminated fields when the plants are wet. Frequent rainy weather increases disease occurrence and severity.
Bean Anthracnose Symptoms and Signs
Leaves, stems and pods of bean plants are susceptible to bean anthracnose.
Seedlings grown from infected seeds often have dark brown to black sunken lesions on the cotyledons and stems.
Severely infected cotyledons senesce prematurely, and growth of the plants is stunted. Diseased areas may girdle the stem and kill the seedling.
Under moist conditions, small, pink masses of spores are produced in the lesions.
Spores produced on cotyledon and stem lesions may spread to the leaves. Symptoms generally occur on the underside of the leaves as linear, dark brick-red to black lesions on the leaf veins.
As the disease progresses, the discoloration appears on the upper leaf surface. Leaf symptoms often are not obvious and may be overlooked when examining bean fields.
The most striking symptoms develop on the pods. Small, reddish brown to black blemishes and distinct circular, reddish brown lesions are typical symptoms.
Mature lesions are surrounded by a circular, reddish brown to black border with a grayish black interior.
During moist periods, the interior of the lesion may exude pink masses of spores.
Severely infected pods may shrivel, and the seeds they carry are usually infected. Infected seeds have brown to black blemishes and sunken lesions.
Bean Anthracnose Management Strategy
The following premium fungicides are recommended for prevention and eradication of bean anthracnose.
- Use either certified seed, approved seed, or seed known to have a long disease-free history. The use of disease-free seed is the most important control measure.
- Do not plant beans for at least two years in land that has carried an infected crop.
- Remove diseased plants, where practical, to help check the spread of disease.
- Avoid cultivating and harvesting an affected crop when wet to prevent the spread of spores.
- Do not pack lightly diseased pods as anthracnose can develop during transport.
- Avoiding unnecessary movement in infested fields
- Planting bean varieties which are resistant to anthracnose
- Treating seeds with BIODISTINCTION XTRA helps to control seed coat infections.
- Whenever conducting any foliar spray, it is highly advisable to mix the fungicide with INTEGRA 3ml/20l, which improves the efficacy of the fungicide by acting as a sticker, spreader and penetrant.
- Timely application of fungicides is very crucial for an effective control
- Alternating different fungicides throughout a plant’s season prevents the fungus from developing resistance over any of the fungicides.