In the fall of 2016, when touring maize study plots, Joe Stephan first noticed the telltale black particles characteristic of tar spots. In those days, tar spot was a relatively new fungal disease that affected maize and could only be detected in certain parts of the Midwest.
“We have an understanding tar spots and knew how to identify their presence through various signs”. However, the illness did not often manifest itself until the later part of the growing season, so we did not anticipate a significant reduction in yield. Stephan, an AgriGold agronomist who works in northern Indiana and southwest Michigan, recalls that very little data was accessible.
Since that, two years had gone.
In 2018 Tar spot not only affected plants but also affected a significant geographic region. According to Stephan, the output plummeted by as much as 20, 30, or even 40 bushels per acre in areas infested with tar. The illness lowers the amount of leaf total area used for photosynthesis, which means less energy, specifically for the development of the plant and the ears.
Since then, tar spot has expanded over the entirety of the Midwest and eastern Corn Belt, impacting a wide variety of states, including Iowa, Wisconsin, Illinois, Michigan, Indiana, and Kentucky. It was found all the way out in Nebraska during the previous season. Farmers are now able to monitor the progression of the illness. The Tarspotter app, which the University of Wisconsin-Madison created, is a helpful tool that helps farmers make management decisions and forecasts disease pressure.
According to Stephan, growers should collaborate with their neighborhood agronomists or crop consultants to build tailored farm and field management strategies. It will help decrease the pressure of tar spot disease and avert potential output losses. The recommendations include awareness of the circumstances that provide:
- A danger.
- Planting corn hybrids that have demonstrated resistance to tar spots in areas that are not likely to have fungicide treated.
- Planning timely fungicide treatments.
Fields at danger for tar spot
The presence of hot and humid weather produces ideal circumstances for tar spots, just as it does for other corn fungal diseases.
Irrigated fields are more prone to the disease because the leaves remain moist for longer. And maize that has been watered tends to grow to a greater height and have larger leaves, both of which trap more moisture in the canopy, as Stephan explains. Because the inoculum can still be found in crop residue, river bottoms, low-lying locations, or fields surrounded by trees may also have an increased risk. This is also true for fields that have been planted in corn following corn.
Trying to interpret the ratings for tar spots
The first step in tar spot disease management is planting hybrids resistant to the illness.
According to Stephan, “the industry has done a decent job of discovering hybrids with tar spot tolerance,” a phrase that can be found in the previous sentence. For instance, AgriGold gives tar spot ratings for its hybrids on its website. These ratings measure tolerance on a scale ranging from one to five, with five being the maximum tolerance level. Stephan adds that various seed manufacturers use different reporting methodologies for tar spot tolerance in their seeds.
Stephan encourages people to “make sure you understand tar spot ratings and talk with their seed provider to discover the proper tolerance level for their crop.” “Focus your efforts on breeding highly resistant hybrids for fields that may be resistant to treatment with fungicides, such as tiny fields or fields that are adjacent to residential areas,” the article advises.
Tolerance for tar spots
One of the farmers, named Matt Sebasty, decided to look into tar spot tolerance after having past experiences with output reductions. In the town of New Carlisle, Indiana, Sebasty cultivates 3,500 acres of land with maize and soybeans.
He recalls, “During the 2020 season, we firstly observed tar spot.” We were caught off guard by tar spot, so we lost more than 30 bushels per acre.
Even though the growing season in 2021 was wetter than average, which created ideal circumstances for the disease known as tar spot, Sebasty was better equipped to combat the problem. He experimented with a hybrid known for its resistance to tar spot called AgriGold A636-16VT2RIB.
Even with tar spot, the hybrid produced 21 bushels more per acre than the normal yield for 2021 on our field.
Those who plant maize must be aware that there is not a hybrid that is immune to tar spots. Even though highly tolerant hybrids should maintain their health for longer, they might still fall victim to the illness. Growers concerned about tar spots must begin planning their fungicide approach as soon as possible.
According to Stephan, “Farmers should start scouting for the illness when the canopy starts to shut, and the humidity starts to climb.” It is important to remember that if it is too rainy to scout, the circumstances are perfect for tar spots.
The timing of fungicide treatments might be unpredictable, but two applications are required in most situations. “When planting their crops, some farmers apply fungicides, and later, when the crop is in the R3 stage, they plan to use aerial spraying.” Others like to spray at the V8 to V10 phases, and then they spray again later,” Stephan explains. If you intend to apply one application, the best time to do so is immediately after tasseling or, if the humidity is particularly high, before tasseling.
Despite this, Stephan urges farmers not to adopt a “wait and see” mentality about tar spots because there may be restrictions on the availability of fungicides and the infrastructure necessary to apply them.
According to him, farmers should be ready for everything and have their fungicide already purchased and ready to use. When you consider the possibility of losing 20 or more bushels per acre due to tar spot, it is highly cost advantageous to spray for it at the corn prices that are now available.