Farm406

Alternaria blight, caused by Alternaria alternata, occurs sporadically and is oen confused with Ascochyta blight. It infects over 400 plant species. e pathogen is seedborne and infested seed serves as the source of inoculum. e pathogen sporulates on seedlings and spreads via conidia (spores). Symptoms include pale brown lesions on leaf margins and tips, particularly on older leaves. Affected leaflets drop off the plant. ere may also be dark brown, elongated lesions on stems, petioles, flowers and pods. Temperatures of 75 to 82°F and high relative humidity (more than 85 percent) favor disease development. Planting resistant cultivars can effectively manage this disease. Decreased plant density and reduced irrigation help reduce disease. Seed treatments can protect seedlings for up to 40 days aer planting, and fungicide sprays can be applied when necessary. FIGURE 5. Anthracnose of lentil stem (A) and leaf (C) lesions. This disease is easily confused with Ascochyta blight (B, D). Anthracnose of lentil is caused by the fungus Colletotrichum truncatum. It was first discovered in Canada, and has since been found in North Dakota and Montana. Where it occurs it can be a very serious disease. Symptoms include tan lesions that begin on lower leaves around 8-12 nodes or first flower (Figures 5A and C). Leaflets drop to the ground and may be the first indication of a serious disease problem. Lesions spread to stems and pods, and can defoliate plants. Deep tan lesions, oen with black borders, can indent the stem, which is characteristic of anthracnose (Figure 5A). Defoliation and girdling can cause plants to wilt and lodge. Seeds from infected plants may be discolored and shriveled, resulting in significant dockage. e pathogen prefers temperatures of 68 to 75°F and 24 hours of leaf wetness. Microsclerotia of the fungus on infested debris can live at least three years. Inoculum oen comes from debrisor seed, and windborne debris can carry the pathogen for many miles. is disease is best prevented by not introducing the pathogen into an area via seed transmission. ere are foliar fungicides available for use. ey should be applied at canopy closure or at the first symptoms of disease. Additional applications for disease control may be necessary. Ascochyta blight is a limiting disease for chickpea production and may require multiple fungicide sprays for management. Pea and lentil are less susceptible to Ascochyta, but the disease can still require careful management depending on the timing and severity of infection and the prevailing weather conditions. e species of Ascochyta are host-specific, so for example, Ascochyta rabiei from chickpea will not infect pea. Ascochyta fabae f. sp. lentis infects lentil, and three different fungal species can infect pea: Mycosphaerella pinodes, Phoma pinodella, and Ascochyta pisi. Lesions from Ascochyta on chickpea are very distinct (Figures 6 and 7). ey are circular or oblong in shape, and may begin as small, light-colored specks on the leaf which expand into target-shaped lesions. Under moist conditions, each 'wave' of the lesion is surrounded by a brown to black halo, accompanied by small black fungal structures called pycnidia under moist conditions. Lesions can occur on stems, petioles, and pods (Figures 5 and 6). Lesions on pea tend to be more restricted, and the 'target' paern tends to be less obvious (cover photo, center). Lesions on lentil are a lighter brown with a dark brown halo, but also oen lack that 'target' paern (Figures 5B and D). Lesions on plant tissue coalesce (Figure 7) and cause defoliation, stem breakage and lodging. Photos: Michael Wunsch, NDSU-Carrington A B C D farm406 54

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