Stewart’s wilt of sweet corn
Dan Egel, Extension Plant Pathologist, SWPAC, Purdue University
Each spring there is a race among gardeners and commercial growers to produce that first ear of sweet corn. There are many obstacles to sweet corn production. Among those obstacles is the disease Stewart’s wilt. Symptoms of Stewart’s wilt include stunting of the plant and a yellow or brown streak that often runs the length of the leaf (Figure 1). Infected plants often produce small, unmarketable ears.
Stewart’s wilt is caused by a bacterium that survives the winter in an insect known as a flea beetle. These insects, less than 1/8 of an inch long, jump like fleas when disturbed. When flea beetles feed on young sweet corn plants, the bacterium may be transmitted to the corn plant, causing Stewart’s wilt.
It turns out that the flea beetle, and thus the bacterium that causes Stewart’s wilt, survives the winter better in warm temperatures. A simple model of flea beetle survival is to add the average temperatures of the months of December, January and February. If the temperatures add up to less than 90, the flea beetle survival is likely to be low and Stewart’s wilt will not be severe. If the temperatures are between 90 and 100, flea beetle survival will be moderate and if the temperatures are more than 100, flea beetle survival will be high and Stewart’s wilt may be severe. Figure 2 shows a map of Indiana with the areas of low, moderate and high flea beetle survival indicated based on the temperatures of the past winter. Growers in areas of high flea beetle survival may want to take extra precautions against Stewart’s wilt including purchasing a hybrid with partial resistance to Stewart’s wilt and/or choosing a seed treatment for sweet corn that helps reduce flea beetle populations. Commercial growers can get more information on Stewart’s wilt in the Midwest Vegetable Production Guide for Commercial Growers (ID-56) available in a hard copy from your county educator or from the Internet at mwveguide.org.
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Figure 1: Symptoms of Stewart’s wilt of sweet corn includes stunting and long, linear lesions that may run the length of the leaf.
Figure 2: This map of Indiana is broken into areas of low, moderate and high flea beetle survival based on average winter temperatures for the winter of 2012/2013. Flea beetles transmit Stewart’s wilt of sweet corn (data courtesy John Obermeyer).