As farm country heads into pollination season, weather conditions have Ken Ferrie concerned about tar spot erupting into a significant yield robber this season. He says he is fielding a lot of grower calls from across the Midwest on the topic.
“Farmers are asking, ‘Is it here, should we spray, when should we spray?’” Ferrie says. “My response is, ‘Do you see tar spot in your fields.’ Finding it is where you need to start.”
As you scout and think you’ve found the disease, an easy way to confirm what you’re dealing with is to take your hand and try to wipe the tar spots off the corn plants (gloves are recommended). If it’s truly tar spot, it won’t wipe off the plants. If you can remove the spots, you’re likely dealing with insect poo.
Ferrie predicts that many farmers in the geography his business covers will encounter tar spot to varying degrees this season. That concern is extended to farmers in northern Iowa, southern Minnesota and central Wisconsin – areas where he says the rains just keep coming.
“Locally (central Illinois), the low humidity in June I think has suppressed the tar spot, but I do expect later infections if this moisture and humidity continue,” says Ferrie, Farm Journal Field Agronomist.
The more difficult prediction for Ferrie at this point in the growing season is how much damage tar spot will wreak in crops.
“Our biggest threat is from what we call homegrown tar spot. The infection comes from within our fields, triggered by the presence of the disease still there,” he says.
“Homegrown tar spot will be more prevalent in your corn-on-corn and in no-till and strip-till fields that still have corn residue from previous crops in them. Everyone under irrigation needs to be on top of this issue, due to the higher humidity,” he adds.
Because very few corn hybrids offer resistance to tar spot, Ferrie advises growers to check all their hybrids for presence of the disease.
“Homegrown tar spot will be the easiest to find below the ear right now. Later, when the disease is windblown around like a morning fog, you’ll find it high on the corn plant,” he says.
Identify Your Group
This season, given commodity prices and the range in crop quality, Ferrie is hearing a variety of different perspectives from farmers on how they plan to deal with tar spot. Farmers are fitting primarily into one of the following four groups.
Group 1 is not going to scout or spray a fungicide at all, because the growers believe products are too expensive and corn is too cheap. This group has probably not lived through the wrath of tar spot yet, in Ferrie’s opinion.
Group 2 is not going to scout, but the farmers plan to make a one-pass fungicide application.
Group 3 will scout fields and pull the fungicide application trigger if needed, based on disease pressure in their fields, pressure in surrounding fields, weather patterns and hybrid type.
“This group is mainly spraying what we call D hybrids, those hybrids that count on depth of kernel fill to get their yield punch,” Ferrie explains. “This group will spray twice if need be.”
Group 4 farmers are not going to scout but plan to spray twice for tar spot, no matter what or if anything shows up. This group has lived through the wrath of tar spot and doesn’t plan on enduring extreme losses from it again.
“They have learned in the school of hard knocks that homegrown tar spot that starts at the bottom of corn plants in late June or early July will eat your lunch at the tune of about 60 bushels per acre, along with down corn,” Ferrie says.
Get Aggressive With Tar Spot
Ferrie offers the following specific recommendations for addressing tar spot this season, given that it’s early July.
For farmers in wet areas where tar spot has been confirmed:
If you’re not going to scout the crop but you have one fungicide application planned, spray the corn at tassel.
“If your corn is uneven due to water damage, wait for the later corn to get tasseled or consult with your supplier on fungicides and surfactants to reduce pinched ear syndrome in corn pre-tassel,” Ferrie advises.
For farmers who are scouting and plan to spray, depending on what they find in the field, Ferrie offers several considerations:
If you see homegrown tar spot low on the plant, spray it. If the corn is not tasseled, take precautions to not get pinched ear syndrome.
“I would plan a second fungicide pass around R3, based on scouting. If no tar spot is present, but other diseases like GLS and northern leaf blight are present above the ear, I would also spray pre-tassel,” Ferrie says.
“If no tar spot is present and other diseases are on the leaves below the ear, our plot results would suggest waiting to spray until brown silk – 10 to 15 days or more after tassel, pull the trigger.
“If your plan is to spray for standability and to protect kernel depth, you’re looking for back-end protection from a fungicide,” he adds.
For farmers who don’t plan to scout fields but plan to spray twice, Ferrie recommends pulling the trigger after all the tassels are out and then a second time about 21 days later.
“On that first spray, I would add an insecticide to make sure you don’t have trouble getting the crop pollinated,” he says.
Key Takeaways on Application Practices
Ferrie says farmers and retailers need to drive their fungicide products deep into the canopy during applications to get optimum results.
If you’re going by airplane, helicopter or drone, he encourages narrowing up swath widths to prevent streaking.
“The bigger droplets that penetrate the canopy are under the aircraft, and the finer droplets tend to stay at the top of the plant, at the outer edges. Flying aircraft closer to the canopy doesn’t give us better penetration, as the air that is bouncing off the ground will catch the spray on its upward lift,” Ferrie explains. “You will most likely have to pay your applicator more to narrow up your swaths.”
On the other hand, if there’s no homegrown tar spot present low on the plants, Ferrie advises “sticking with full-width spraying to keep as much of the product as possible at the top of the plant, protecting those money-making leaves.”
Interested in learning more agronomic insights and practical information from Ken Ferrie? Be sure to join us for the annual Farm Journal Corn & Soybean College, fast approaching on July 23-24 in Heyworth, Ill. Here’s the full details.
Be sure to get all of Ferrie’s recommendations on how to deal with tar spot in this week’s Boots In The Field podcast:
