The Tar Spot complex has more questions than answers when trying to plan for the 2019 growing season, but the AgriGold Agronomy Team has put together their insights on some management strategies.
Reduce the stress level in the corn crop:
Corn fields that were under severe stress from various sources seemed to be the quickest fields to be impacted by Tar Spot. Thus, these fields were also the fields typically with the largest yield loss associated with the Tar Spot complex.
Strategies to help reduce stress and thus help reduce a hybrids susceptibility:
Adequate Nitrogen Program – Using a multi-faceted approach when managing nitrogen. Apply at multiple times using multiple forms will help ensure a season long supply of nitrogen for the corn crop. Also, be ready to apply a rescue treatment if excessive rainfall causes severe denitrification.
Crop Rotation – Tar Spot does overwinter, with less corn residue on rotated acres there is potentially less inoculum for future infection. Also, less stress with crop rotation, less potential insect pressure that potentially reduce root function and water uptake.
Incorporate fungicides into the management plan:
A tassel application of a fungicide labeled for Tar Spot is a critical piece to keeping the corn plant healthy and producing grain. Keeping as much staygreen into the plant is critical to slow late infections of Tar Spot once the fungicides has run its course. Greener, healthier plants were able to better tolerate and continued to produce grain longer than plants weakened by other foliar diseases.
There appears to be some slight differences between genetics and Tar Spot infections. There is also a maturity and/or growth stage difference as well. Ultimately all hybrids seemed to become infected at some point and their yields were reduced. Hybrid selection continues to focus on putting the right genetic on the right acre using our Field GX strategy. Next year will bring a new set of challenges and if a grower solely chooses hybrids based on a supposed tolerance to Tar Spot, next year challenges and yield environments may not fit those genetics. Using past performance and implementing the Field GX strategy will provide growers with security and confidence of what they are planting and why.
Below is a list of AgriGold hybrids with color coded ratings to Tar Spot. Dark green represents hybrids that are showing the most tolerance to Tar Spot and would be an excellent choice if Tar Spot is of concern. The red hybrids indicating an extreme lack of tolerance in which these hybrids would NOT be recommended to use if Tar Spot is of concern.