The challenges of this growing season continued in September when a storm front brought more than 3 inches of rain to much of the state. While the rainfall was welcome for pastures and cover crops, it added to the challenges in cornfields, especially those suffering from drought and the derecho. Rainfall, followed by warm temperatures, will further predispose the stressed corn plants to issues like stalk rots and ear rots.
Field agronomists across the state have noted the corn appeared to lose significant standability. Farmers should monitor fields to be harvested. Checking for standability can help prioritize fields with significant stalk rot for earlier harvest to reduce harvest losses, the stress of slow harvest and future issues with volunteer corn.
WEAK STALKS: Careful scouting and harvesting of fields according to crop condition can help prevent field losses due to low stalk quality.
A couple methods exist for monitoring fields for stalk rots: the “pinch test” and the “push test.”
Pinch test. Check the stalk firmness by pinching the lower internodes near the ground between your thumb and forefinger. Be concerned when stalks crush easily.
Push test. Push the plant at shoulder height about 30 degrees from vertical. Be concerned when plants pinch over and fail to snap back to a vertical position.
Regardless of the method chosen, check a minimum of 100 plants per field, preferably by evaluating at least 20 plants in five different areas. If more than 10% of plants in a field crush easily or lodge, this indicates stalk rot may be an issue, and that field should be prioritized for harvest. This year may present special challenges in doing these checks due to downed corn, but we suggest farmers do their best to check several areas of fields. You may need to use multiple field entrances to check different areas whenever possible.
Several stalk rots might be present in crop fields. Use the resources listed here to learn more about the different types of stalk rots we can see in fields. For more information or in-field assistance, reach out to your local ISU Extension field agronomist.
- anthracnose stalk rot
- bacterial stalk rot
- diplodia stalk rot
- fusarium stalk rot
- gibberella stalk rot
- pythium stalk rot
While we like to take advantage of as much field drying of corn as possible, there are many fields this year where it’s rather risky leaving the corn out there very long. While you are checking fields for stalk rot, also check for ear rots. Read the article Drought and derecho increase mycotoxin risk in 2020 Iowa corn crop-scouting and monitoring fields.
Anderson is the ISU Extension field agronomist for central Iowa. Contact firstname.lastname@example.org.