When people are under stress we’re more likely to come down with the flu. Our bodies are focused on managing the stressor and not on fighting the flu virus—which gives it the upper hand. It’s the same with corn, and right now much of the crop is stressed across the Corn Belt. Whether it’s too much rain or too little, that stress is giving stalk rot pathogens in the plant an advantage, which could mean trouble when harvest comes.
“In areas where we have hot and dry weather there is water stress, which is causing corn to cannibalize the stalk to fill grain,” says Alison Robertson, Iowa State University Extension field crops pathologist. “In the East where it’s been wetter that stress and lower light days can reduce photosynthesis—causing more stress.”
Anytime corn is stressed photosynthesis is reduced, which limits carbohydrate production and increases risk of stalk rot. The rots you see could be different depending on your stress, wet or dry.
“Where it’s hot and dry there might be some charcoal rot and where it’s wet maybe more gibberella, but I would expect to see anthracnose and fusarium everywhere,” Robertson says. “I expect to see more stalk rots this year and wouldn’t be surprised if there are more standability issues than last year, too.”
If you start seeing any of the below stalk rots in your fields this year be sure to perform the “pinch” or “push” test for standability. If 10% or more of the stalks crush when pinched or lodge when pushed you’ll want to schedule that field for an early harvest.
Small black, round sclerotia inside the stalk that look like charcoal dust
Infects plants under drought stress conditions and more likely when soil temps are above 90°F and soil is dry
Irrigating or planting earlier, planting hybrids with resistance or later to avoid dry periods can help mitigate this disease
Gibberella Stalk Rot
- Small round, blackish specks on surface of stalk rind and pinkish-red discoloration inside the stalk
- Overwinters in crop residue and infects the plant in warm, wet conditions
- Hybrid resistance is uncommon, avoid other stresses such as insect leaf tissue damage to reduce likelihood of gibberella infection
Anthracnose Stalk Rot
- Shiny black lesions on stalk with black fungal material just beneath the surface
- Overwinters in residue and requires high humidity, warm temperatures and expended periods of cloudy weather favor the disease
- Look for hybrids with stalk rot resistance, avoid stress and consider tillage to bury crop residue
Fusarium Stalk Rot
- White fungal growth on the outside of the stalk with pink or salmon color on interior stalks
- Favors dry weather prior to silking and warm, wet weather after silking, feels spongy when performing squeeze test
- Overwinters in crop residue, hybrids with resistance to other stalk rots might carry some resistance to fusarium