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Tar Spot Moves into the Midwest

July 27, 2020
This agronomic image shows tar spot

Reports of tar spot making its way into the Midwest are now official, with confirmed sightings in MI, WI and IN. Remember that proper identification is key. Note that while fly specks are often misidentified as this fungal disease because they can resemble tar spot in the field, these black specks are easily rubbed off with water.

Tar spot overwinters in fields on decaying corn stalks and is carried easily in the wind. You’ll know tar spot by its dark spots on the leaf surface, but it infects the plant well before these symptoms are visible. It has a long latent period, meaning that corn can be infected 14 days or more before spots are visible, so the disease could be causing costly damage to your plants before you’re able to see it.

Though recent hot, dry conditions have kept the disease to a minimum, we all know that conditions can, and will, change. To help better understand and manage this disease, here are a few things to consider:

  • Tar spot is favored by cool and wet conditions. Lower nighttime temperatures, foggy mornings, wind driven rain and overhead irrigation are all factors that make a more favorable environment for the disease.
  • Plan to treat fields that are most at risk. These include fields that are corn-on-corn, irrigated and/or planted with varieties which tend to be more disease susceptible.
  • Preventive applications of fungicides give the best opportunity to manage disease. Infections present in vegetative stage corn will most likely require a 2-pass fungicide program to best mitigate potential losses.
  • To correctly identify this disease, first wet the speck and try to rub it off the leaf’s surface. If the spot rubs off, then it is not tar spot. If it does not rub off, then it may be tar spot and should be sent to a lab for confirmation.
  • To help keep track of the progression of this disease in your state, use the map here.

Trivapro® fungicide is a proven, effective management tool for tar spot. The 3 robust active ingredients in Trivapro, including Solatenol® fungicide, provide preventive and curative disease control and plant-health benefits, helping growers stay a step ahead of tar spot.

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