Anthracnose of beans

Anthracnose of bean is mainly a seed-borne disease caused by the fungus Colletotrichum lindemuthianum. It has a wide host range on many legume species including those grown as vegetables and grain legumes.

The disease can cause serious losses in bean crops in temperate and subtropical zones. It is now considered rare in commercial bean production in Australia due to the introduction of certified seed schemes.

Host plants

The disease infects:

• french beans
• mung beans
• broad beans

There are several races of the fungus. Varieties such as Tweed Wonder, Wellington Wonder and Redlands Beauty are resistant to the most common race, but they can be severely affected by other less common races.

Symptoms of anthracnose

The following symptoms can indicate anthracnose:

• infection on leaves, stems, petioles, pods and seeds of bean plants
• leaves – angular reddish-brown spots on leaves with veins, especially on the under-leaf surface showing dark streaks (Figure 1)
• stems and petioles – dark brown, sunken, circular to elliptical, 1 cm to 2 cm diameter lesions that may girdle the stem (Figure 2)
• pods – small reddish-brown, slightly sunken circular spots form on the pods that rapidly turn into larger, dark-sunken lesions, which if severe may distort the pod
• seed – yellow to brown lesions on seed, which may be underdeveloped and produce poor germination
• lesions – especially on stems, petioles and pods show dark brown fruiting bodies from which oozes an exudate of pink to orange spores

Controlling anthracnose

To control anthracnose:

• use either certified seed, approved seed or seed known to have a long disease-free history
• do not plant beans for at least 2 years in land that has carried an infected crop
• rogue diseased plants to reduce the spread of the 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

Spread of disease

The fungus can spread by planting infected seed. Spores can be splash dispersed by rain, overhead irrigation, and wind within the crop.

Environmental conditions

The disease develops quickest in warm, damp conditions.

The optimum temperature for symptoms to appear is between 18°C and 25°C, but they are delayed or prevented by temperatures outside the range of 7°C to 33°C.

Survival of the fungus

The fungus can survive on contaminated seed. Survival on crop debris in the soil can vary from a few months to several years depending on temperature.

References

Koike ST, Gladders P, Paulus AO (2007) Vegetable Diseases, A colour handbook. Manson Publishing 448pp.

Persley D, Cooke T, House S (2010) Diseases of vegetable crops in Australia. CSIRO Publishing 292pp.