Published on Thursday, February 27, 2020
Anthracnose is a common fungal disease in most corn production areas of the United States. These symptoms are caused by the fungus Colletotrichum graminicola. This fungus can cause many issues in corn including early- and mid-season leaf blight, top dieback, and stalk rots. In severe cases, these diseases can lead to premature death of infected plants, stalk lodging and reduced harvestability, and loss of grain yield.
C. graminicola overwinters in infected corn residue as mycelium or sclerotia. During the spring, spores are produced from the over-wintering structures. The fungus can enter corn plants through roots and stalk wounds, carried by wind, or by being splashed onto young plants from residue. The most favorable conditions for disease development include wet weather and warm temperatures. Symptoms of anthracnose can begin to develop during the early vegetative growth stages and can continue throughout the plant’s life depending on infection type (leaf blight or stalk rot). Anthracnose diseases are most common in corn-after-corn rotations due to increased levels of inoculum.
Early-season symptoms of anthracnose are usually in the form of a leaf blight on the lower portions of the plant. However, leaf blight symptoms can move further up the plant later in the growing season if conditions are favorable. Mid- to late-season foliar blight isn’t as common as early-season blight due to less favorable conditions for disease development. Disease lesions can be up to 1 in. long and ½ in. wide, but are typically around ¼ to ½ in. long and oval to spindle shaped. Lesions are brown in color with yellow to pink to purple edges. Multiple lesions can merge, resulting in larger areas of tissue death and eventually, dark fungal fruiting bodies (acervuli) will develop in the dead leaf tissue. These fruiting bodies will form black, hair-like spikes called setae that can be observed with a 20 to 30x hand lens. In severe cases, premature death of infected leaves may occur.
Top Dieback and Stalk Rot:
Top dieback typically begins in randomly scattered plants with purpling or yellowing of the flag leaf. This stage of anthracnose damage typically occurs mid-season, within a few weeks after pollination. These symptoms can be caused by other issues like drought stress, corn borer damage, and other environmental stress factors, so proper identification is important. Top dieback is caused by an anthracnose fungal stalk rot in the upper portions of the plant. This rot blocks the flow of water and nutrients to the upper portions of the plant, resulting in the death of the upper leaves and tassel tissues.
Anthracnose stalk rot is one of the most common stalk rots of corn production in the United States. The only difference between typical stalk rot and top dieback is the location of the rotted stalk on the plant. These symptoms typically occur in the lower portion of the stalk late in the growing season. It can be identified by shiny, black lesions on the outside of the stalk; discoloration of the internal portions of the stalk at the nodes; and weak, easily crushable stalks that are prone to lodging. As with the other forms of anthracnose, setae can be seen with a hand lens emanating from the acervuli.
Under normal conditions, anthracnose leaf blight is typically not serious and does not warrant a fungicide application. The presence of early-season leaf blight and later stalk rot are not always correlated, though they are both caused by C. graminicola. Resistance of corn hybrids to leaf blight does not necessarily confer resistance to stalk rot and vice versa. For these reasons, a fungicide treatment to control early-season foliar anthracnose does not remove risk of later-season top dieback or stalk rot issues. However, fungicide applications can reduce the impact of anthracnose infections by helping maintain and improve overall plant health.
Other Management Practices Include:
Author: Scott Dickey
Categories: Agronomy, Agronomy Talk