Foliar Diseases Showing up in Corn

Foliar diseases, especially gray leaf spot, are beginning to show up in some corn fields, and questions are being asked about the need for foliar fungicides. This is not surprising, since we have had several warm and humid days over the past two weeks, with dew and fog during the mornings. These are the conditions favorable for gray leaf spot. However, we have also received reports of leaf rust, eye spot, and northern corn leaf blight.

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, gray leaf spot usually develops late and has very little or no effect on the crop. This will certainly be the case in some fields again this year. However, we have already received reports of gray leaf spot at or above the ear leaf in some areas.

Because of the wide variation in our planting dates this year, with some fields planted in late April and others planted in late May, the corn crop is at growth stages ranging from about V10 (ten-leaf stage) to brown silk across the state. With such a wide variation in crop development, if the weather continues to be favorable for disease development, some fields and some hybrids could certainly be infected early and could suffer yield reduction if not treated.

Scout fields for foliar diseases, especially those planted with susceptible hybrids in an area with a history of gray leaf spot or northern corn leaf blight or in a continuous-corn, no-till field. These fields are the ones most likely to benefit from a fungicide application. Use hybrid susceptibility, weather conditions, field history, and current disease level as guide when making a decision to apply a fungicide. There are several very good fungicides to choose from.

Follow the labels and keep your eyes on the fungicide price and application cost when making a decision: http://www.oardc.ohio-state.edu/ohiofieldcropdisease/corn/Corn%20foliar%20fungicide%20chart%202008.pdf  

By Pierce Paul, Dennis Mills