Be Alert for Corn Anthracnose

Anthracnose in corn is caused by the Colletotrichum graminicola fungus which possesses the potential to cause early- and late-season leaf blight, stalk rot and “top-kill” or “die-back” (when upper leaves may die before those in the center). Corn anthracnose can be found throughout the Corn Belt from the Mid-Atlantic states to Nebraska.

While anthracnose is typically a secondary pest not likely to cause problems every year, it warrants a watchful eye for signs of infection throughout the corn growing season, including pre-harvest and post-harvest management for future crops. The disease can manifest itself when environmental conditions and other stresses create an ideal scenario for targeting high-yield corn potential. Corn anthracnose is most typically seen in no-till and reduced-tillage farming systems.

Identification and Lifecycle

Under ideal environmental conditions, corn anthracnose goes through three phases in its lifecycle, with each phase posing a different threat to corn development and yield. Corn anthracnose can be identified by the distinct symptoms exhibited during each phase.

Phase one – Anthracnose first appears as leaf blight and can occur soon after corn emergence. At this stage, blight will show up on lower leaves as uneven, water-soaked round spots. During late July or August, late-season anthracnose blight symptoms may spread to upper corn leaves following pollination. Eventually, spots or lesions on the corn leaves will grow to ¾ inch long and look tan in the center, with borders varying from yellow to red or brown in color. The presence of anthracnose leaf blight in a field does not necessarily mean that the disease will advance to further stages, however.

Phase two – At this stage, corn anthracnose appears as top die-back, which is a sign of stalk rot. During this stage, the lower part of the corn plants looks green and the portion of the corn plant above the ear prematurely dies. Top-kill or die-back may occur as early as one to three weeks after tasseling.

Phase three – During this lifecycle stage, corn anthracnose causes root infections or stalk rot. The corn anthracnose fungus is even more likely to occur as a stalk rot than a foliar infection. Anthracnose stalk rot is the most common corn stalk rot and occurs late in the growing season. It is seen initially in the rind tissue as narrow, vertical or oval-shaped lesions. Unlike other corn stalk rots, anthracnose exhibits distinctive black blotches in the rind tissue.

Similar to many crop diseases, corn anthracnose primarily overwinters in crop residue left in the field from the previous season. Anthracnose infection spreads by both air and water. Spores can be splashed on leaves by rain or blown in by wind. Extended periods of cloudy, wet and warm weather provide favorable conditions for anthracnose disease development. Low fertility can also facilitate anthracnose in corn.

The stalk rot phase of corn anthracnose is distinctive. Black streaks and blotches, sometimes covering the entire stalk, appear on the surface of the lower stalk late in the season. The pith also becomes shredded, turning dark gray to brown. Photo courtesy of AgStock Images/Bill Barksdale.

Crop Damage

When corn is heavily infected with anthracnose leaf blight, lesions may merge to cover entire leaves, which wither and die.

The top die-back (Phase 2) stage of anthracnose is the most damaging to yield because of stalk rot and leaf loss. Phase 3 of corn anthracnose occurs late in the season, leading to lodging and harvest problems.

It’s possible for an early corn anthracnose infection in root stalks to cause plant death before pollination. A more common effect during the stalk rot phase is corn plants dying from anthracnose just before maturity. When several nodes are rotted, the entire corn plant dies. Compared to other types of stalk rot, lodging from anthracnose happens higher up on the corn stalk.

Overall, most yield loss from corn anthracnose results from premature plant death, which ultimately stops grain fill and causes lodging to complicate harvest.

Managing Corn Anthracnose

Farmers can benefit from several options to manage corn anthracnose, including hybrid selection, scouting, cultural practices and fungicides. A combination of these crop protection practices provides optimum security to enhance corn yields and should be implemented to sustainably manage corn diseases.

Hybrid selection

Choosing corn hybrids with genetic disease resistance offers the best economical and effective defense against corn anthracnose and other diseases. Be aware that corn hybrids with resistance to anthracnose corn leaf blight might not also have resistance to the stalk rot phase. Seek recommendations from a local seed dealer to determine corn anthracnose disease ratings and help determine the best hybrids for individual fields and regions. Even partial disease resistance goes a long way to protect corn yields.

Scouting

Early and frequent scouting for diseases is a routine best management practice to tackle pest problems before they lead to economic damage. In the case of corn anthracnose, look for lesions on the lower seedling leaves. A hand lens can help detect black spots in lesion centers. The anthracnose leaf blight phase typically doesn’t occur after corn reaches knee-high. Following the leaf blight phase, scout for corn anthracnose symptoms every three weeks when plants are between the knee-high and whorl growth stages, according to University of Kentucky.

Cultural practices

Crop rotation remains a solid tactic to help diminish disease threats. Any type of tillage that reduces crop residue from a previous corn crop will help manage corn anthracnose and other diseases overwintering in crop residue. When field history shows anthracnose disease problems, farmers may want to consider using tillage that chops and buries residue and rotating away from corn for a year.

A combination of integrated management practices such as disease-resistant hybrids, crop rotation, proper nutrient management and insect, weed and disease management – with chemicals, if needed – are especially recommended in continuous corn grown with no-till and reduced-tillage cropping systems, according to University of Illinois Extension.

Fungicides

Foliar fungicides may be applied early in the growing season to corn seedlings as a risk-management tool for anthracnose leaf blight and other corn diseases, including corn eyespot and northern corn leaf blight. When anthracnose leaf blight is identified, application during early corn growth is critical for maximum fungicide effectiveness.

Delaro™ fungicide offers preventative and curative defense against yield-robbing diseases, including gray leaf spot, northern corn leaf blight, anthracnose leaf blight and southern rust. This versatile fungicide has application flexibility — at-tassel timing (VT to R2), in combination with a herbicide (V4 to V7) and/or in between (V8 to VT). Delaro can be applied by air, ground or by chemigation and can be mixed with adjuvants, herbicides, insecticides and micronutrients.

Before applying any fungicide, please read the entire label for the best possible results and to confirm that the product is effective on the disease you need to control. Not every product is suitable for every situation, and correct application technique will ensure the best results.

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