Anthracnose is a fungal disease that under warm, moist conditions can significantly reduce edible bean yields and seed quality by staining the beans.
The pathogen responsible for anthracnose in edible beans is Colletotrichum lindemuthianum, and has more than 15 races or strains.
Anthracnose in lentils is caused by a different species of Colletotrichum and will not infect edible beans.
Anthracnose is primarily seed-borne, but can develop from infected bean residue and contaminated equipment under certain conditions.
Early season symptoms of the disease appear on the undersides of leaves, where small angular brick-red to purple-brown lesions develop.
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Older leaf lesions become darker and extend through to the upper leaf surface and proceed along the veins. Pod lesions are circular, sunken brown to black colored. There are often rings of black dots within the lesion.
Anthracnose was first identified in Manitoba two years ago and during the summer of 2000 several fields had high levels of the disease.
These hot spots were due to several factors.
The warm, moist weather during June and July was ideal for anthracnose development and spread.
Other factors revolved around questionable production practices: the use of bin run seed, tight rotations (beans on beans) and not using a proper seed treatment.
Foliar fungicides are not registered and American reports suggest that they have limited effectiveness against anthracnose.
The disease must be managed through decisions made before seeding time.
Resistant varieties
There are only a limited number of recommended varieties for Manitoba that are resistant to some races of anthracnose, but not necessarily the one or ones found in Manitoba.
There is no complete screening of the edible bean varieties grown in Manitoba, Ontario and North Dakota to determine which race or races, if any, they are resistant to.
Pathogen-free seed
Certified seed is recommended because anthracnose is primarily spread through infected seed. This guarantees the variety’s genetic quality and integrity.
But certified seed has no guarantee regarding seed-borne disease status. Some lots of good quality bin-run seed can have as low or lower levels of anthracnose on the seed as does certified seed.
Low level infections can be hard to spot within a field so even fields assumed to be anthracnose-free might not be so.
Questionable seed lots can be analyzed for $55.
Labs doing this work including 20/20 Seed Labs at 877-420-2099 and Discovery Labs at 306-249-4484.
Proper seed treatment
DCT (diazinon, captan, thiophanate-methyl) is the only registered seed treatment recommended for control of seed-borne anthracnose on edible bean planting seed.
Even if planting seed is treated with other fungicides, it should be treated with DCT because no other fungicide contains the thiophanate-methyl component that provides anthracnose control.
Control with DCT is dependent on thorough seed coverage on lightly to moderately infected bean seed.
Crop rotation
The pathogen can survive on infected bean residue to produce an infection the following spring.
A crop rotation of three years out of beans is recommended.
After initial infection, the disease is spread by splashing raindrops carrying spores to adjacent plants and by spores being moved by people, animals or equipment through wet fields.
Spore spread of up to 4.5 metres has been observed in Ontario when splashing raindrops are blown by gusting winds.
