Bean anthracnose, a potentially devastating disease, remains a concern for edible bean producers in North Dakota. It has been found in southern Manitoba, Michigan, and Ontario. Anthracnose has been found in commercial fields in several North Dakota counties since 2001.

Anthracnose is a serious disease that can be easily overlooked by growers. In fact, symptoms of anthracnose on bean pods can look similar to those of bean bacterial blight. The main difficulty with anthracnose, in addition to seed-borne transmission, is that under low infection levels it may be difficult to detect in the field. Low infection levels in the seed have the potential to cause a severe outbreak of the disease the following year under optimal conditions. Thus, testing for anthracnose is extremely important.

To date, no certified bean seed produced in North Dakota has been found to contain anthracnose.

Symptoms

Field symptoms of anthracnose appear as small, angular brick red to purple-brown lesions on the bottom of leaves. Later, these lesions become darker, extend to the upper leaf surface, and proceed along veins. Pod lesions are sunken, circular in shape with brown to black coloring that have a dark margin surrounding the lesion. There is typically a thin zone of red tissue around the lesion. On the lesion surface, tan spores dry into dark granular masses. Lesions on seed can be similar in appearance to pod lesions. Bean anthracnose is easily spread by infected seed, rain splashing, and by being blown from field to field on crop residue. This disease can result in significant yield losses.

Control
The North Dakota State Seed Department has taken measures to ensure certified bean seed produced in North Dakota is free from this serious pathogen. In 2002, North Dakota imposed mandatory anthracnose testing on all certified seed grown in the state.  Additionally, service testing is being promoted and utilized by the seed industry on seed lots offered for sale in North Dakota.

Growers should be alert as to where the seed they are purchasing comes from. Seed from known infected areas should be avoided.

The use of certified seed that has been field inspected and lab tested for anthracnose is recommended. Good management practices are important for prevention of anthracnose. Growers should avoid planting bin run seed.   

Testing
The anthracnose test is a requirement for certification of dry edible bean in North Dakota. We strongly encourage all edible bean seed producers to test each field separately for anthracnose. Testing each field separately is important if seed from a number of different fields is commingled into a single seed lot. If seed from a field containing anthracnose was commingled with other fields that did not contain anthracnose, the entire seed lot would then become contaminated.

The Seed Department currently conducts a 1,000 seed grow-out test for bean anthracnose that requires a minimum of 14 days to complete. Seedlings are evaluated for the presence of the anthracnose causing fungus Colletotrichum lindemuthianum. A positive test result indicates the sample is contaminated, resulting in failure. Growers should be aware of the sample size a testing lab uses to conduct an anthracnose test on edible bean. Sample sizes of 200-400 seed may not be large enough to detect the presence of anthracnose. Growers must submit a two to three pound sample for this test. Bacterial Blight (Dome Test) can be performed at the same time as an Anthracnose test. Submit at least three pounds of seed for a Dome test and Anthracnose test. For these tests, a good representative sample of the seed lot is important, as very low levels of anthracnose infection are a serious problem. This test is a pass or fail test and any positive test result will result in a failed test.