As harvest 2015 is moving into October, more Iowa cornfields are showing signs of weakening stalks, and possible lodging problems if the corn is left standing too long before harvesting it. What happened? Why are we seeing more stalk rot this year?
The 2015 growing season was challenging as the weather was extremely variable within each region of Iowa, agronomists point out. Today's modern corn hybrids can fight through most of these situations and look fine, but the last few weeks of the grain filling period is where the plant is sometimes forced to rob from the reserve nutrients in the stalk, and use those nutrients to finish filling out the kernels on the ear.
"This weakens the stalk and puts standability at risk for the later part of the harvesting season," says Brian Lang, an Iowa State University Extension field agronomist at Decorah in northeast Iowa. "Corn plants that were stressed during the 2015 growing season are more susceptible to invasion by stalk rot and then become more prone to lodging at harvesttime."
More fields showing signs of weaker stalks for potential lodging
Agronomists generally agree fields at risk for stalk lodging should be harvested as soon as corn grain reaches around 25% moisture go ahead and harvest to prevent yield loss from corn that can easily fall down, especially when strong winds begin blowing.
"If it's in late September or the calendar has flipped into October and you walk through a field and push stalks with your hand and they easily fall over, we recommend harvesting that corn," says Lang. "Once such fields are down to 30% to 35% grain moisture content, harvest them and spend the money to dry the corn in your bin or in an on-farm drying system. Or take it to the elevator and have it dried. With fields that are showing signs of lodging, you are taking a big risk trying to field-dry corn."
Fuel costs to dry corn are cheaper than they've been in years
Fuel cost for artificial drying is cheaper this fall than it's been in a number of years, notes Charlie Hurburgh, a grain storage and handling specialist who is also head of the Iowa Grain Quality Initiative at ISU. "Even at $3 or $3.50 per bushel corn, with propane at a $1 a gallon or below, it will pay you to harvest the corn wetter than you normally do and run it through a dryer or dry it in a bin. If you check corn in your field now and find stalk rot present and conclude that your corn is likely to have problems with stalk lodging, go ahead and harvest that grain now, a little wet," he advises. "It's cheaper to dry it than to lose it."
Conditions during the 2015 growing season that have led to weak stalks include saturated soils that had nitrogen loss or developed crown rot and/or root rot, notes Lang. Also, leaf disease pressure reduces the plants' ability to absorb sunlight and make nutrients to feed the developing stalks and ears. Cloudy days also reduce the amount of sunlight available to corn plants. Corn rootworm feeding on roots adds to the stress on corn plants.
Stressed corn plants are more susceptible to stalk rot invasion
"The stalk rot disease organisms must be present for stalk rot to occur, but an accumulation of stresses to the corn plant during the growing season greatly enhances the chance for stalk rot infection and spread," says Lang. "In general, the 2015 growing season was rather wet early, then there was very little rain from late July to late August here in the northeast area of the state. Nitrogen was running a bit short in some fields, and heavy leaf disease pressure was evident in some fields."
Many fields had the lower leaf canopy wilting back prematurely, some from nutrient deficiencies and/or drought stress. Some fields had the upper leaf canopy shutting down prematurely from excessive leaf disease or top-dieback (another form of stalk rot). "As leaf photosynthetic area is reduced by disease and nutrient deficiencies, the stalk's nutrients will be further cannibalized to fill the ear, putting more stress on the stalk," Lang explains. "The point being, there is a fair amount of stalk rot in fields across northeast Iowa this fall. Farmers need to scout their cornfields now to determine which ones are at a greater risk of lodging. Those fields that are in danger of the corn falling down should be harvested first."
How to scout fields to check for cornstalk rot
You can test the firmness of a stalk by pinching the lower internodes with your thumb and forefinger, he says. Healthy stalks are firm and cannot be compressed. If a stalk can be compressed or feels soft, it is rotted and is a good candidate for lodging. Check at least 100 plants per field. That is, 10 to 20 plants in five to 10 different locations.
Different corn hybrids and fields with different tillage, rotation or fertilization histories should be scouted separately. If a field has more than 10% to 15% of the stalks rotted, significant lodging is likely to occur and the field should be targeted for a more timely harvest, says Lang.