Description and Symptoms
Anthracnose Stalk Rot (Colletotrichum graminicola) is likely the most prevalent stalk rot in the eastern United States. Affected plants have shredded piths and die prematurely. Anthracnose also causes a distinctive blackening of the stalk rind. Initially, these areas are narrow, water-soaked lesions, but they turn very dark and shiny and can join together to form large black blotches or streaks over the growing season. Anthracnose also can cause a top dieback, where the stalk above the ear dies four to six weeks after pollination.
The fungus overwinters in corn residue and infects plants through the roots or by spores that splash onto the stalk or are carried by insects that may introduce them into feeding wounds. Seedlings can be infected, and some plants may die before pollination. The disease usually does not appear until late in the season and occurs more severely where corn follows corn, especially in reduced tillage.
Resistance to anthracnose is available in some hybrids. Rotation and tillage will reduce inoculum. If more than 10 to 15 percent of stalks are observed to be rotted 40 to 60 days after pollination, the field should be scheduled for earliest possible harvest.
- Scout R5 through R6 (Pythium and bacterial stalk rot can cause premature death at any time).
- Pinch lowest aboveground internode; if it easily crushes, it indicates stalk rot.
- Check at least 100 plants selected from throughout the field.
- If more than 10 percent of stalks are easily crushed, harvest the field early. Be aware of drying costs for early harvested grain.
To determine if stalk rot is a problem in your field, do the “pinch test”. At several areas in the field, pinch the lowest internode of a few corn stalks in several locations in the field. If more than 10 percent of the stalks can be pinched, schedule an early harvest since standability may be an issue.
Photo by Adam Sisson