In a normal year, you’d be done scouting for stalk rots. But this isn’t a normal year. Especially in areas with weather conditions that lead to greater changes of disease, this type of scouting is critical.
As you walk through fields, first perform push and pinch tests to determine fields that are at risk of lodging.
“When you think about stalk rots, they are opportunistic, so anything that causes stress amplifies the opportunity for stalk rot,” says Andrew Friskop, North Dakota State University Extension cereal crop plant pathologist. “I typically prioritize fields with over 20% [of the plants that fall], but it becomes a problem when we’re looking at 60% to 80% of plants that fail the push test.”
When you’re scouting, look for a few general symptoms. With stalk rot, you will typically see wilting, premature dry down, lodging and plants that fail the push or pinch test. Check about 100 plants and stay away from the end rows to properly assess field conditions.
Here are four common stalk rots to look for:
Anthracnose Stalk Rot
- Look for shiny black lesions on the stalk with black fungal material just beneath the surface.
- Anthracnose favors high humidity, warm temperatures and extended periods of cloudy weather.
- It can over winter in residue, so consider hybrids with stalk rot resistance. Avoid stress and consider tillage to bury the crop residue.
- Scout for dark gray or black colored pith, which can cause plant death.
- Charcoal rot infects the plant after pollination, and it favors hot and dry weather where crops have insect damage.
- It will overwinter in plant residue, so consider planting earlier or planting hybrids with resistance earlier next year.
Diplodia Stalk Rot
- If diplodia is in your fields, it infects the stalk through the roots, crow and lower stem. It also has dark brown or black spots on the outer stalk—they feel rough to the touch.
- Plants with prior injury from insects are more likely to get the disease.
- When looking for seed next year, try to find hybrids with resistance.
Fusarium Stalk Rot
- Watch for white to pink fluffy growth on outer nodes and deterioration of the inner stalk that turns tan to brownish.
- The disease favors dry weather prior to silking and warm, wet weather after silking. Plants with Fusarium stalk rot will feel spongy when performing the squeeze test.
- Fusarium overwinters in crop residue, so when shopping for seed next year, look for hybrids with resistance.
- Insect injury and disease history increases the likelihood of occurrence.
Gibberella Stalk Rot
- This disease deteriorates the inner stalk following pollination. It will appear as reddish vascular bundles and small black specks on the surface.
- Warm, wet weather can push gibberella to damaging levels and plant stress and insect injury increases the likelihood of the disease.
- When looking for seed next year, hybrid resistance is uncommon, and the disease overwinters in crop residue.
If you wait for corn to dry in fields, you could lose yield from lodged corn. Be sure to scout now to prioritize what fields to harvest first to ensure you pick up as much grain as possible.
Know the impact lodged corn has on yield. Premature plant death can lead to drastic yield loss, depending on how early it dies, according to Wyffels. Here’s what kind of yield loss you should expect if plants lodge, by stage:
- Silk- whole plant 100% yield loss, just leaves 97% yield loss
- Blister- whole plant 100% yield loss, just leaves 73% yield loss
- Milk- whole plant less than 75% yield loss, just leaves 59% yield loss
- Dough- whole plant 50% yield loss, just leaves 41% yield loss
- Dent- whole plant 40% yield loss, just leaves 23% yield loss
- Half Milk- whole plant 12% yield loss, just leaves 7% yield loss
- Black Layer- no yield loss
Nitrogen-poor areas might be at greater risk of poor stalks because the plant “steals” nitrogen from the stalk to feed the ear.
“Regardless of which stalk rot pathogen causes the primary infection, the end result is the same: yield loss due to lodging or premature plant death,” according to Wyffels research