How to Manage Pests
UC Pest Management Guidelines
Ascochyta Blight (Garbanzo Beans)
Pathogen: Ascochyta rabiei, Didymella rabiei
(Reviewed 8/07, updated 12/08)
In this Guideline:
Ascochyta blight is a serious disease of garbanzo beans. Symptoms develop on all aerial parts of the plant at any stage of growth.
On seedlings, brown lesions that develop at the base of the stem may lead to damping-off like symptoms.
During or after cool, rainy weather, foliar symptoms first appear on leaves as circular light brown lesions with no margins. As the lesions continue to develop small, black, raised spots (pycnidia) form in concentric circles within the lesions and are a good diagnostic characteristic of the disease.
Dark brown stem lesions weaken the stem, which often breaks. Lesions on pods are similar to those on leaves and result in poor seed set. Pod infection may also lead to discoloration and shrinkage of the seed. Developing beans can become infected and, if used for seed, can lead to early infections in the next crop. Overall, severe infections lead to general plant blight.
The fungus overwinters on infected garbanzo debris left in the field or in or on seed. During wet weather, spores are released from pycnidia and are splashed or carried in rain or irrigation water. (This is the asexual spore stage that has been identified as Ascochyta rabiei.) Once plants become infected, new spores are formed that spread to adjacent plants, creating expanding areas of diseased plants in fields. Symptoms develop 3 to 6 days after infection; moderate temperatures (68° to 77°F) and wet weather are optimum for severe disease.
Another type of fruiting body, pseudothecia, may develop when both compatible mating types of the fungus are present. Spores produced in pseudothecia are airborne and may play an important role in long-distance dispersal of the pathogen but are not important in local and short-term disease development. This is the sexual spore stage, which is identified as Didymella rabiei.
The use of tolerant cultivars is one of the most effective and economical disease management practices. However, because more than one Ascochyta mating type has been identified, host plant resistance/tolerance to the disease is good for a limited number of growing seasons. Currently available public and private varieties with tolerance to most or all mating types identified in California include Sierra, Dylan, HB-14, Sutter, San Joaquin, and recent releases of the Airway Farms (AWF) series.
In susceptible varieties, cultural practices can be effective in managing this disease. Always use clean seed, rotate away from garbanzos, and thoroughly incorporate infested garbanzo residue. Crop rotation of 2 to 3 years will eliminate inoculum in the soil because the fungus won't survive in the absence of garbanzo host tissue. Wide row and plant spacing may increase ventilation between plants and reduce favorable conditions for plant infection.
Always plant seed that has been treated. Foliar applications of fungicides limit the rate of disease spread. Apply fungicides at first sign of disease and re-apply according to the label if rainy weather is forecasted. Thorough coverage of the plant canopy is important.
UC IPM Pest Management Guidelines:
R. M. Davis, Plant Pathology, UC Davis
Acknowledgment for contributions to Abiotic Disorders:A. E. Hall, Botany and Plant Sciences, UC Riverside
Acknowledgment for contributions to Diseases/Abiotic Disorders:S. R. Temple, Plant Sciences, UC Davis
Acknowledgment for contributions to Diseases (viruses):R. L. Gilbertson, Plant Pathology, UC Davis