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Issue No. 21, Article 5/August 15, 2008

Diplodia Leaf Streak: An Uncommon Disease of Corn in Illinois

Diplodia leaf streak, caused by the fungus Stenocarpella macrospora, was observed in research plots at the Dixon Springs Agricultural Center recently. Although Diplodia leaf streak has been observed in Illinois in the past, its occurrence is not common. This disease is not to be confused with Diplodia stalk and ear rot, which is caused by a similar but different fungus. Symptoms of Diplodia leaf streak appear as large lesions on the leaves, with "black spots" inside the lesions. These black spots are called pycnidia, which are structures of the fungus that produce asexual spores. With the size of the Diplodia leaf streak lesions, one could possibly confuse them with symptoms of northern corn leaf blight. Lesions of northern corn leaf blight will appear slightly more cylindrical (cigar-shaped) than those of Diplodia leaf streak. Also, the pycnidia in the Diplodia leaf streak lesions are much more easily observed than any dark spots of fungal sporulation that may occur in northern corn leaf blight lesions.

Diplodia leaf streak on corn. Note the "black spots" within the lesion, which are known as pycnidia.

Because Diplodia leaf streak is so uncommon, no known management practices are available. The research trial in which this disease was found was planted into corn stubble. It is likely that the fungus was surviving in the stubble and favorable environmental conditions for the disease occurred. The risk of this disease likely increases when planting into corn stubble.--Carl A. Bradley

Carl A. Bradley

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