Pioneer Urges Anthracnose Management

DES MOINES - Jun 26/06 - SNS -- Yield losses from anthracnose, one of the most common stalk rot diseases faced by corn growers in the United States, can reach 40%, making it clear growers need a management strategy to tackle the disease.

"Growers may see stalk rot when the early-season growing environment encourages heavy kernel set and when the late-season environment is stressful," says Gary Munkvold, research coordinator - pathology, entomology, and seed science for Pioneer. "Yield loss is due to reduced grain fill, premature plant death and stalk breakage or lodging."

Anthracnose is caused by the fungus Colletotrichum graminicola. This fungus can attack corn plants at different stages, causing leaf blight and crown rot of seedlings. It also causes leaf blight, stalk rot and top dieback of adult plants.

"Growers can identify anthracnose stalk rot by the appearance of shiny black blotches or streaks on the stalk rind," says Munkvold. "A gray mold also can appear in the deteriorated stalk pith."

Stalk rot can be the result of the combined effects of more than one organism that attacks a plant approaching maturity. Therefore, identification can be difficult and other pathogens may be involved, including Gibberella, Fusarium or Diplodia.

Leaves above the ear may turn grayish green, yellow or reddish, then die and collapse. This is referred to as top dieback. Top dieback normally takes place four to six weeks after pollination, while the lower stalk remains green and before the lower leaves begin to wither and die.

Plants with stalk rot are vulnerable to lodging, so growers should monitor fields and combine fields with stalk rot first. Producers should begin scouting for stalk rot when corn reaches 30% to 40% moisture.

"Growers also need to keep in mind that prevention is the best weapon to keep anthracnose at bay," says Munkvold. "Hybrid selection, crop rotation, insect control and avoidance of stresses due to fertility and moisture all help prevent anthracnose."

Munkvold adds that corn growers should select hybrids with good standability and high yield potential that are recommended for their growing area. Pioneer brand corn hybrids are currently rated according to their resistance to anthracnose stalk rot.

Crop rotation with nongrass crops in conjunction with a deep plowdown of corn residues is beneficial in preventing a buildup of the anthracnose pathogen in the soil. Balanced soil fertility, particularly that having adequate nitrogen and potassium, is important.

Any soil conditions that interfere with availability and uptake of water and nutrients also can promote stalk rot. That means growers should avoid soil compaction and herbicide injury, plant an appropriate population, control weeds and use good irrigation practices where available.

Damage from stalk-boring insects like European corn borer can promote stalk rot, so management should include control of these insects.