Ascochyta Blight (Garbanzo Beans)

Ascochyta blight is a serious disease of garbanzo beans. Symptoms develop on all aerial parts of the plant at any stage of growth. Brown lesions develop at the base of seedling stems that may lead to symptoms similar to damping-off.

During or after cool, rainy weather, foliar symptoms first appear on leaves as circular light brown lesions with no margins. Over time, small, black, raised spots (pycnidia) form in concentric circles within the lesions. Pycnidia are a good diagnostic characteristic of the disease.

Dark brown stem lesions cause stems to weaken or break. 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. Severe infections lead to general plant blight and decline.

The fungus survives on infected garbanzo debris left in the field or on the outside or inside of the seed. The fungus survives only on crop debris, not in soil. It does not produce resting spores to survive in soil. How long the debris can persist before decomposing depends on the climate condition. It lasts longer in drier conditions.

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 (68º to 77ºF) and wet weather are optimal conditions for severe disease development.

Another type of fungal fruiting body, the 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, although they 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 varieties is one of the most effective and economical disease management practices. However, because more than one Ascochyta (asexual stage) mating type has been identified, host plant resistance can change over time as the pathogen evolves. Check with local experts (UCCE or seed supplier) regularly. Currently available public and private varieties with tolerance to most or all mating types identified in California include Sierra, Dylan, Sutter, San Joaquin, and the Airway Farms (AWF) series. Some varieties have more tolerance than others. Check with your seed warehouse supplier to determine the variety that performs best in your area. Keep stands healthy, as the disease resistance can break down in stressed fields.

Cultural practices can be effective in managing this disease:

• Always use certified, disease free seed.
• Thoroughly incorporate infested garbanzo residue to hasten decomposition and to minimize the possibility of spore production and dissemination.
• Rotate to other crops for two or better three years. That will eliminate inoculum in the soil because the fungus will not survive in the absence of a garbanzo host.
• Avoid early plantings (November and early December) since they result in large plants and a thick canopy, which provides ideal conditions conducive to disease development.
• Consider wide row and plant spacing. This increases ventilation between plants, reducing favorable conditions for plant infection.

Use treated seed to avoid introducing the fungus to the field. Foliar applications of fungicides limit the rate of disease spread. Apply fungicides at first sign of disease and reapply according to the label if rainy weather is forecasted. Thorough coverage of the plant canopy is important.