Disease Profile – Leaf Blotch Diseases of Wheat
Carol Groves, Plant Pathology, UW-Madison, Damon L. Smith, Plant Pathology, UW-Madison/Extension
Leaf blotch is a complex of common fungal diseases of small grains (e.g., wheat, barley, oats and rye), and many grasses. In Wisconsin, winter wheat is the most important commercial crop affected by these diseases with potential yield losses of up to a 30%. Leaf blotch diseases are generally favored by cool, wet, windy weather.
Symptoms of leaf blotch diseases usually first appear between the veins of lower leaves as chlorotic (i.e, yellow), water-soaked flecks that enlarge to become dry, yellow, then red-brown, blocky to oval lesions, sometimes surrounded by yellow haloes. Some leaf blotch fungi can infect glumes in seed heads as well as leaves. Rows of tiny black specks (reproductive structures of leaf blotch fungi) are often visible in mature lesions.
Several species of fungi can cause leaf blotch. These include Septoria and Stagnospora species. Leaf blotch fungi survive in infested residues, seeds, volunteer wheat plants and some weed grass hosts. Initial infections typically occur in the fall as seedlings emerge, and are caused by spores (called ascospores) that are produced on wheat residue from a previous wheat crop. Additional infections can occur the following spring and are due to spores (called conidia) that are produced in lesions on infected wheat plants.
Successful management of leaf blotch can be accomplished through an integrated approach that combines use of resistant varieties, pathogen-free seed, crop rotation, proper crop debris management, volunteer wheat eradication, and fungicide treatments.
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