by: Pierce Paul, OSU Extension
Foliar diseases, especially Gray Leaf Spot (GLS), are beginning to show up in some corn fields. This is not at all surprising, given that the crop was planted relatively late and it has been wet and humid in some areas. GLS is favored by humid conditions, particularly if temperatures are between 70 and 90 F. Foliar diseases of corn are generally a concern when they develop early and progress up the plant before grain fill is complete. This is especially true when the hybrid is susceptible. In most years, GLS and NCLB usually develop late or remain restricted to the lower leaves. However, if it continues to rain and stays humid, this will likely not be the case this year.
Due to wide variations in planting dates, weather conditions, and hybrid maturities, the corn crop is at growth stages ranging from emergence to tassel across the state. Now is the time to start scouting those early-planted fields for foliar diseases, especially those planted with susceptible hybrids in an area with a history of foliar diseases or in a continuous-corn, no-till fields. Those are the fields most likely to benefit from a fungicide application. Use hybrid susceptibility, weather conditions, field history, and current disease level as guides when making a decision to apply a fungicide.