Anthracnose leaf blight (Colletotrichum graminicola) seldom causes yield loss. Early in the season, lower leaves usually show symptoms first. Later, symptoms can occasionally be found on upper leaves. Leaf lesions are oval or spindle shaped, tan or brown with dark brown or purple margins, up to 1-inch-long and 1/2 inch wide. As the disease develops, the fungus produces black, spiny fruiting structures on the dead leaf tissue. These are visible with a 30X hand lens. On severely infected leaves, the lesions can grow together into large dead areas. These leaves may turn yellow and wither.
The fungus overwinters as mycelium or sclerotia in corn residue or seed. Spores are spread primarily by splashing water. Disease development is favored by wet weather during early crop growth with moderately warm temperatures. Anthracnose leaf blight is most common where corn follows corn. Disease develops soon after planting and continues to develop until canopy closure.
This disease is best scouted through V2 through V8. Typically, the first foilar disease during the growing season. More prevalent in fields with infected corn residue such as those with reduced tillage and continuous corn.
Although some products are marketed for Goss’s wilt management, there are still few data on their effectiveness. In 2012 we evaluated several products (Procidic, 42-Phi Cu, EcoAgra and Elixor), but we were unable to detect a treatment effect because we had very low incidence of the disease at all our locations.
While an application of a fungicide at V5/V6 would likely reduce common rust and anthracnose leaf blight, these diseases rarely cause yield loss on corn in Iowa. Most hybrids have good resistance to common rust, plus as the season progresses it usually gets too hot (>80F) for the disease to continue to develop. Resistant hybrids and inbreds are available. Crop rotation and tillage reduce survival of the fungus and foliar fungicides labeled for anthracnose leaf blight are available.
Photo by Gary Munkvold