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Stay vigilant for tar spot in cool, wet conditions
Retailers can help farmers save bushels per acre by keeping tar spot top of mind and helping their customers make timely decisions around fungicide applications.
Tar spot is a foliar disease that favors high relative humidity and cooler temperatures (60 F to 70 F), quickly spreading through the corn canopy under those conditions. Without timely management, tar spot causes rapid premature leaf senescence, reduced stalk quality and yield loss.
Early detection is the first step in protecting yield. Ron Geis, Corteva market development specialist in Iowa, said scouting for tar spot is critical and becomes increasingly important during cool, humid times of the season.
“As a fungal disease, tar spot follows the pattern of the disease triangle, which includes a host, pathogen and the right environment,” Geis said. “We need to be on high alert if we have cooler, wet conditions, especially if the forecast looks like those conditions will continue.”
Geis said it’s important for farmers to watch for tar spot earlier in the year, but scouting for tar spot should continue all season long.
“When we get into late August or early September, temperatures start to cool down and we can get late-season rains, and those conditions can favor tar spot,” Geis said. “You really don’t stop scouting for tar spot, as long as that plant is trying to pack starch into those kernels and put on yield.”
When looking for tar spot, farmers should examine corn leaves for ascomata, which are black oval or circular lesions that look like small droplets of splattered tar. The best way to confirm tar spot, Geis said, is to give the leaf a scratch test.
“There are a few other things that can cause black spots — for example, insect feces can be mistaken for tar spot,” Geis says. “The recommendation is to try to scratch it off. If it doesn’t come off, then it’s probably tar spot.”
When it comes to management, retailers can help growers make three critical decisions about fungicide applications.
First, growers need to determine when to spray. If tar spot is in the field, Geis recommends applications sooner than later.
“Once tar spot is confirmed, you want to make a fungicide application as soon as possible. From a control standpoint, we are always better off to be ahead of the game,” Geis said. “If you delay until higher levels of infestation, you’ll have more-advanced stages of disease, and no product will resurrect dead tissue. So it’s very important to prevent future disease development.”
Second, growers need to determine what fungicide to apply. Geis recommends products with two or three modes of action, such as Forcivo® fungicide or Aproach® Prima fungicide. Forcivo fungicide offers three effective modes of action, including a novel SDHI, to protect with overlapping preventive and curative activity. Aproach Prima fungicide is a broad spectrum, long-lasting fungicide with both a curative and preventative mode of action.
Third, growers should consider if they will need to make one or two applications based on disease pressure, field conditions and history. If two applications are warranted, growers should lead with the fungicide with the most modes of action.
“I always tell growers to start with the heavier hammer, and university studies back that up,” Geis said. “If growers lead with Forcivo, they may be able to come back with Aproach Prima, but it’s better to get more preventative modes of action in the field earlier.”
Retailers play an important role in helping growers navigate fungicide decisions, especially encouraging them to scout early and make applications as soon as possible if disease is confirmed. Retailers can help growers reach higher yield potential by reminding them to stay vigilant and act fast.
“When it comes to fungicide applications, it’s better to be a little early than to be too late,” Geis said. “Retailers can partner with growers to ensure they protect plant health and yield potential in a timely manner.”
Aproach® Prima and Forcivo™ are not registered for sale or use in all states. Contact your state pesticide regulatory agency to determine if a product is registered for sale or use in your state. Always read and follow label directions.