В Северной Каролине подтвердили появление грибкового заболевания тар-спот на кукурузе

N.C. Cooperative Extension - Iredell County Center Tar spot, caused by the fungus Phyllachora maydis, was confirmed in Randolph and Davidson Counties, NC, in August 2026. The recent rains and lower temperatures likely helped to promote tar spot development. The development and spread of tar spot is generally favored by moderate temperatures between 60-80°F, humidity greater than 85 percent, and leaf wetness for more than seven hours per day. Scouting tips Scouting will be especially important if wet weather continues. Phyllachora maydis is only known to affect corn. The tar spot fungus produces small (1/16-3/4 inch), round to irregular, raised black structures called stromata (Figure 1) on both the upper and lower surfaces of corn leaves. Stromata may also develop on leaf sheaths, husks and tassels. Occasionally, tan to brown "fisheye" lesions with dark borders can develop around the stromata (Figure 2). Physoderma brown spot, common and southern rust, and insect frass can be mistaken for tar spot. Table 1 summarizes the characteristics that can be used to distinguish among them. When disease develops late, especially after R4-R5, yield impacts are often minimal. The optimal window for a single fungicide application is generally between tasseling (VT) and milk (R3) stages for suppressing disease, protecting yield and getting return on investment. Fungicides applied after R5 will not provide these benefits. So, this late in the season, no. But if you decide to make one or more fungicide applications, be sure to leave untreated check strips and calculate the associated costs and benefits so that you can accurately determine your return on investment. If you suspect tar spot in your field, contact your county Extension office and submit samples to the Plant Disease and Insect Clinic. This content is sourced from N.C. Cooperative Extension - Iredell County Center . It reflects the author's views and has not been edited by our newsroom. It may have been generated using AI assistance.