When it comes to tar spot on corn, it’s not a matter of if, but when. In 2023, corn growers in the Midwest can expect to see tar spot continue to spread throughout the corn belt. However, despite the onward march of this fast-acting pathogen, there are ways to prepare for it and mitigate its impact this season.
Tar spot originated in Mexico and spread into South America in the 1950’s and 60’s. It arrived in the United States in 2015, when it was discovered in Michigan. Since then, it has spread to nearby states to the south, east and west. In 2021, after only six crop seasons, losses due to tar spot were double the amount of the next leading disease in corn.
Tar spot is a highly detrimental disease that can desiccate plant tissue quickly and inhibit effective grain fill late in the season. There are two ways it can be identified in corn. Sometimes, the disease creates a halo effect with a dark center. In other cases, it results in speckles across the plant. Either way, it still has a black, tar-like appearance that progresses very rapidly.
Tar spot functions similarly to gray leaf spot. It overwinters, and it can lay dormant without a host. It is a particularly challenging disease because it’s always in the field once the pathogen is in the area. When it develops all depends on the environment. Tar spot develops most when the plant has extended periods of leaf wetness (greater than 6 hours). Humidity, wind-driven rain, and extended periods of fog are also contributors to the promotion of the infection. The only reason it didn’t turn into a major problem last season was thanks to the drought across the Midwest.
A single-pass strategy, as with other diseases in corn we deal with, often works on infestations happening in the very beginning of reproduction or shortly thereafter. However, infestations occurring during vegetative growth will require a two-pass strategy to control this pathogen. The most commonly used fungicides offer 21 days of protection, so the vegetative pass should be immediately followed up by the next pass. If there is any gap in preventative coverage, tar spot can quickly take off and reduce bushels until the second application. Helena’s Odyssey™ and Avaris® 2XS are two premium options to add to your rotation. Both provide multiple modes of action along with preventative and curative control. Talk to your Helena representative about the right product for your program and availability in your area.
Disease management is an essential part of a comprehensive Corn Wise™ program. Being Corn Wise means putting the right tools in place at the right time to maximize your corn crop, and ultimately, your ROI. To finish out your 2023 plan and learn more about tar spot and how it may be affecting your area, contact your local Helena representative.