In many areas, corn has already reached chest to shoulder height, and with rapid vegetative growth comes increased disease pressure. A leading concern for corn is Tar Spot, which was confirmed in Rock County, Wisconsin on July 3.
As we approach the V10 growth stage, now is the time to consider your fungicide strategy. Early scouting and timely application could make all the difference. When Tar Spot reaches 50% severity on the ear leaf during grain fill, yield losses of 20–60 bu/ac have been reported.
Caused by the fungus Phyllachora maydis
Looks like small, raised black circular lesions on stalks, leaves, and husks
(These spots cannot be rubbed off)
Most frequently appears between silking and late grain fill
Can overwinter on infected residue left on the soil surface
Cool temperatures
High humidity
Prolonged leaf wetness
Irrigated fields are especially susceptible
Confirmed presence in PA, IN, IL, IA, MO, KS, NE, and now WI means this disease is active and spreading.
We recommend evaluating your fields now, especially if you’re nearing V10 or have a history of Tar Spot pressure. If you’d like help scouting or building a fungicide plan, our agronomy team is ready. Contact your Premier agronomist today to get started.
