ProVision Agronomist Shares Tips on Fighting Tar Spot

By Josh Schulner, ProVision Agronomist at Hixton

Posted: 8/10/2022

Tar spot is a fungal disease that affects the leaf structure of the corn plant. This disease was first diagnosed in southern Wisconsin in 2016. At that time, tar spot was thought to be mostly cosmetic. It appeared as little black tar droplets on the leaves of the corn plant.

Then, in 2018, a severe outbreak of the disease caused substantial losses. Not until late 2020 did we see tar spot as far north as Jackson County. Again, it was intriguing but not a concern.

Last year’s infection was much worse and caught us completely off-guard. It resulted in the premature death of the corn crop, standability problems and yield losses up to 100 bushels per acre.

Today, evidence of this disease can be found in fields throughout ProVision Partners’ territory. Tar spot infections have been reported as far north as Chippewa County and have caused great damage to many corn fields. Exaggerated by other diseases like northern leaf blight and stalk rot, tar spot makes the crop die back even quicker.

What is ProVision doing? Your ProVision agronomy department is fighting this windborne fungus with a combination of tools.

First, we’re working with our customers to promote corn-soybean rotations that break the cycle of the disease. We’re encouraging them to bury infected plants with deep tillage, and we’re recommending they plant hybrids resistant to tar spot.

NOTE: Several varieties growing in our Answer Plots show good resistance to this fungus and yield as well as non-resistant hybrids. We can also provide application of fungicide by grounddriven or aerial applicator, whichever is best. In fact, we’re finding that two applications of fungicide during the season offers nearly perfect control of the disease.

Ground-driven fungicide applications require 20 gallons per acre of water, while air applications require 3-4 gallons per acre for the same coverage.

Aerial application reduces the need for a carrier. Air drafts penetrate the canopy of crop and give you better coverage. Airplane, helicopter or drone, depending on the scale, is usually better than ground driven, and there’s less wheel traffic, so you’re not running over the crop.

NOTE: Drones fit our area with some fields being less than 20 acres to apply, which fixed wing and helicopters don’t want.

Another Benefit of Drones

The other thing these drones will allow us to do is apply a cover crop to our highly erodible ground earlier in the season. Usually, we’re harvesting after the last frost, but a drone can seed a cover crop down through the canopy of an existing crop before it is harvested. That’s significant because it usually takes 5-6 weeks to establish a cover crop for before the first killing. By applying a cover crop, we can capture some carbon credits, keep our soil in place, and secure any carryover nutrients for the following year.

“Drones?” you ask. Yes. I do believe we’re seeing the future approach in leaps and bounds. The old days of the wheel driven machines will someday end if we can send these drones—and even bigger ones—out from home base (your local agronomy center) like bees from a hive.

ProVision will be one of the first . . .

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