Manage Tar Spot Effectively
Tar spot continues to expand across the Corn Belt, with most infestation reports coming from fields planted to continuous corn and/or irrigated corn. While the potential for economic losses from this disease is significant, maintaining good soil health and providing supplementary plant nutrition can greatly help to minimize its impact.
A preventative fungicide program remains a key tool for managing tar spot. Fungicides can be tank-mixed with Ag Spectrum’s foliar nutrition program of PT-21®/Score®/GroZyme®. Be sure to choose a fungicide specifically labeled for tar spot control. To achieve optimal coverage and absorption, keep total spray volume under 10 gallons per acre. Additionally, even when using spray water treatments such as Ag Spectrum’s Indicate 5® and Insure®, it’s always a good practice to perform a jar test for compatibility before heading to the field.
Before making any fungicide applications, it’s critical to scout your fields and accurately diagnose the disease. The University of Minnesota offers these tips for identifying tar spot:
- Tar spot symptoms appear initially as flecking and mild chlorosis (yellowing) on leaves, stalks and husks.
- The black tar spots form after the flecking or yellowing. These spots are the fungal structures called stromata, which are embedded in the plant tissue. They are elongated, raised and cannot be removed by rubbing them.
- The symptoms and signs can develop at any corn growth stage throughout the summer, but typically develop most severely in the late summer.
Focus scouting efforts between growth stages V12 and R2. If tar spot symptoms appear on the ear leaf or the leaves just below during this window, it’s time to apply a fungicide mix labeled for tar spot control. Several products currently available combine triazole and strobilurin active ingredients, and most offer comparable efficacy against the disease. There is little concern if tar spot is seen only occasionally (e.g. < 20% of plants) after corn completes R3.
It’s also important to remember that complete implementation of the Maximum Farming System plays a valuable role in reducing crop disease pressure. Crop stress is a primary contributor to disease development, and a comprehensive nutrient management plan that mitigates stress throughout the growing season is essential. By fully integrating the Maximum Farming System, you can help protect your crops and reduce the risk of economic losses from diseases like tar spot.
