It's late spring, and despite all of the challenges, you've produced a stand of corn with potential for an excellent yield—if things go well the rest of the season. But many corn diseases—including ear rots, such as Gibberella, Diplodia and Fusarium, and other residue-borne diseases—could be a bigger threat than usual this year because of all the inocula lying out in the field on old crop residue.
The high volume of old crop residue is the result of delayed tillage due to wet weather. "About 70% to 80% of corn diseases are carried over in crop residue,” says Farm Journal Field Agronomist Ken Ferrie.
You can fight back against disease pressures, and now is the time to plan your attack strategy.
Here's why Ferrie is urging farmers to be especially vigilant against disease this year: "The stage is set for corn diseases to increase,” he says. "The likelihood of disease is based on three conditions called the disease triangle—a susceptible host crop, the pathogen and the weather. If one leg is stronger than usual—inocula, in this case—the other conditions don't have to be as perfect in order to trigger an outbreak.”
As always, the overriding factor will be weather, says University of Illinois Extension plant pathologist Carl Bradley. "When we see less tillage, there will be more potential for inoculum,” he explains. "But with single-year rotations, such as corn and soybeans, there usually is enough of the host debris left in the field to carry on the pathogens.”
Here are eight steps you can take to control diseases:
1. Do your homework.
"Learn all you can about the diseases you've been having trouble with,” Ferrie says.
"Understand the ideal conditions for each one to develop and its life cycle. Then you will know what problems to expect in 2010.
"Keep in mind that if residue management is recommended as a control measure, the disease organism is carried over in crop residue,” he adds.
2. Bone up on fungicides.
"You must know what fungicide to apply for each disease, and when to apply it,” Ferrie says. "It's not a matter of simply applying whatever product your supplier happens to sell.”
Some fungicides are preventive in nature, which means they must be applied before a lot of disease damage has occurred. Others are curative, which means they can be applied later. "But all fungicides work best if they are applied at the early onset of disease,” Bradley says.
"Keep in mind which leaves you are trying to protect the most—the leaves closest to the ear,” he continues. "A preventive application can still be effective if lower leaves have the disease but the important leaves are still disease-free.
"In my studies, tassel emergence or slightly after seems to be the best timing for corn fungicides,” Bradley adds. "This year, applications very early in the season—at the V5 stage or so—are being talked about; but, in general, disease pressure is very low, or even absent, at that time. Unfortunately, there seems to be very little data available, either from companies or universities, on these early fungicide applications to corn.”
(Bradley and Ferrie both plan to conduct early application research studies in 2010.)
3. Scout fields.
The timing of a fungicide application depends on whether a disease is present and how fast it is progressing. That requires scouting your fields.
"Under ideal conditions, it usually takes 10 to 14 days for a disease to get started,” Ferrie says.
Base your scouting on the weather. "Whether the weather has been cool and wet or hot and dry for the past seven to 10 days tells you what diseases to expect,” Ferrie says. "If you don't have your own weather station, you can get more information from Internet weather sites.
"If you don't start scouting fields until you see a plane spraying fungicide on a neighboring farm, it may be too late,” Ferrie warns.
As you scout, weigh disease risk factors in each field, Bradley says. These include the susceptibility of the hybrid, the previous crop and whether the weather is favorable for the disease, such as frequent rainfall or high relative humidity.
4. Appoint a specialist.
Finding time to scout and doing it in a systematic manner can be easier said than done. "Pick a key employee and make him or her responsible for managing pests, including diseases,” Ferrie says. "Equip him with a good scouting
manual. If no one on your farm has time for the job, hire a crop scout.”
5. Don't get blown away.
Although residue-borne diseases are likely to be especially troublesome in 2010, don't forget that some diseases, such as common rust and southern rust, are blown in by wind.
6. Plan how to apply.
If you think you're likely to need an aerial applicator, talk to one ahead of time and provide maps of your fields. "If aerial application is not possible in some fields—because of nearby houses, for example—you'll need to find a high-clearance ground applicator,” Ferrie points out. Finding an applicator early can save you crucial time in a disease event.
7. Don't let up.
When it comes to residue-borne diseases, plan on a multiyear struggle. "Last year, corn following corn had the worst disease levels,” Ferrie says. "Strip-till and no-till corn following soybeans had the second worst levels. It's all about the amount of residue left because that's where the inoculum survives.
"In 2010, if you're growing corn after corn in a conventional tillage situation, you should have positioned your hybrid based on last year's diseases, using information provided by your seed dealer.
"In 2011, strip-till and no-till corn in a corn–soybean rotation will face a higher disease risk than corn grown with conventional tillage because of the higher residue levels,” Ferrie says.
"With Gibberella, Fusarium and Diplodia, there's so much inocula in the residue that it will take several years to work through this,” he adds.
8. Consult local experts.
Certain diseases are a greater threat in some areas than in others. "In Minnesota, leaf diseases rarely reach treatable levels,” says Dean Malvick, University of Minnesota Extension plant pathologist. "However, you need to stay alert to diseases because some year they could reach treatable levels.”
Next Year's Corn Disease Battle Plan
A disease battle plan for your crops begins right after harvest and continues through the following growing season. It includes tillage, crop rotation, selecting the best hybrids, awareness of weather conditions, scouting and fungicides.
The postplanting steps are covered in the adjacent story. This fall, after harvest, start your 2011 disease management planning by reviewing your 2010 disease issues.
"Sit down with your seed dealer and think about where you had disease problems and how severe they were,” says Farm Journal Field Agronomist Ken Ferrie. "In 2011, avoid planting susceptible hybrids in those fields. When you study test plot results, look at disease ratings as well as yield.”
Plan to rotate your hybrids. "In continuous corn, never plant the same hybrid two years in a row in the same field,” Ferrie says. "If you do, its weaknesses, such as disease susceptibility, will be dramatically expressed.” In his experience, failing to rotate hybrids in a field of continuous corn, where residue is left on the surface, can cost up to 60 bu. per acre.
If you were able to do tillage in some fields but not in others, plan to plant your most susceptible hybrids in your clean-tilled fields.
You can e-mail Darrell Smith at email@example.com.
- Late Spring 2010