Diagnosis and Management of Ascochyta Blight of Chickpea
by Weidong Chen (center of image), Research Plant Pathologist USDA-ARS, Washington State University, Pullman, WA 99164
Ascochyta blight caused by the fungal pathogen Ascochyta rabiei is an important disease of chickpea. Despite important research progress on this disease, Ascochyta blight is still a persistent major disease of chickpea in the US and elsewhere. In the past couple of years we have seen inoculum built up. We should be on the lookout for the disease this growing season. The disease symptoms occur on all above-ground parts of chickpea plants. Early signs of the disease include necrotic lesions with water-soaking margins (Fig. 1).
Fig. 1. Water-soaking margins of initial necrotic lesions on leaves of chickpea.
The lesions enlarge and the pathogen multiplies by producing a black dot-like structure called pycnidia in seven to 10 days. Pycnidia are arranged in concentric rings on leaves and pods and in an oval shape on stems (Fig. 2).
This is a characteristic symptom diagnostic of Ascochyta blight. When the disease starts to spread, small brown circles of dying plants could be seen from distance (Fig. 3).
Fig. 3. Small brown circles of dying plants showing the disease is spreading.
Ascochyta rabiei survives the winter season on infected chickpea straw or on infected seeds. Planting resistant or tolerant cultivars, field rotation, and proper seed treatments are important pre-planting control measures. The pathogen produces ascospores on the previous year’s chickpea debris during the winter months. The ascospores are dispersed by the wind for miles away and land on chickpea plants to initiate infection. The pathogen also produces conidia in pycnidia on infected plants throughout the growing season under moist weather conditions. The conidia ooze out during moist weather and are spread by rain splash for a short distance and can initiate and repeat the disease cycle. The optimal conditions for the disease are rainy or moist weather with temperatures ranging from 16 to 25 C.
During a growing season, the only available management practice is fungicide application. There are several effective fungicides available for managing Ascochyta blight. Contact your local agri-chemical companies for availability. It is important to alternate fungicides of different classes, from year to year or within a growing season when more than one application is required, to prevent the development of fungicide resistance in the pathogen population. Ascochyta blight development is dependent on the weather. Cool and moist weather favors the disease, but dry and hot conditions can suppress the disease. Consequently, it is prudent to consider weather forecasts in making decisions of spraying fungicides.
Dr. Michael Wunsch, Plant Pathologist for the Carrington Research Extension Center (CREC) of North Dakota State University provided a great video on Ascochyta Blight in Chickpea (EMBEDED BELOW), and you can read his primer on Ascochyta Blight on the NPGA website: