P&PDL Picture of the Week for
July 18, 2011

Anthracnose on cucumber

Dan Egel, Extension Vegetable Pathologist, SWPAC

Anthracnose on cucumber, a common fungal disease, has recently been confirmed on samples submitted to the PPDL from northern Indiana. The first symptom one is likely to notice of this disease is the foliar lesions that are 1/8 to 1/4 inch in diameter. Although the lesions are mostly round, many have jagged, irregular edges (Figure 1). If one has a hand lens, it might be possible to see the small hairs (technically setae) that are associated with the mass of spores on the lesions (Figure 2). In mass, the spores are orange or salmon in color. If one looks through the microscope, the spores (technically conidia) are oblong and have little color (Figure 3). When severe, the disease can also cause sunken lesions on fruit. This disease can also affect cantaloupe and watermelon. The best way to control this disease is to choose a variety that has resistance. It is always a good idea to practice crop rotation. If cucumbers need to be watered, it is best to avoid overhead irrigation since this can spread the disease. Home gardeners who choose to use fungicides will find that products with the active ingredient chlorothalonil will be among the products that will slow the spread of anthracnose. Commercial growers should consult the Midwest Vegetable Production Guide for Commercial Growers. Growers may also use this Extension bulletin: Vegetable Diseases: Anthracnose of Cucumber, Muskmelon, and Watermelon

Click image to enlarge

Figure 1. Lesions of anthracnose on cucumber are round with jagged edges.

Figure 2. Using a hand lens, it is possible to observe small hair-like structures (technically setae) among the orange colored mass of spores.

Figure 3. If one were to look in a microscope, the spores would be oblong and lack color.

Purdue Plant & Pest Diagnostic Lab Purdue Cooperative Extension Service