With most of the early planted corn beginning to tassel in the last week to ten days, and what originally looked like a drier, hot forecast turning into a more seasonal, warm, humid forecast with decent rain chances, farmers are beginning to now be faced with the decision of “if and when” to apply a fungicide to what has the potential to be a high yielding corn crop.

The big disease farmers seem to be worried about when making fungicide decisions is Southern Rust. Luckily, this disease does not overwinter in Kentucky, and must be brought up from the Gulf Coast by weather systems every year. You can track the path of Southern Rust via the Southern Rust IPIPE Map found online at corn.ipmpipe.org/southerncornrust.

This map is updated weekly. The good news is Southern Rust currently is only as far north as Central Arkansas and Central Alabama. This probably is an average track for Southern Rust, or maybe even a little behind most years. Here in Central Kentucky, we typically won’t see Southern Rust until at least a week after it’s been found in our Southern Kentucky counties. The bottom line on Southern Rust is, there is no need to apply a fungicide now to protect against Southern Rust. In fact, if you do, even the longest lasting products we have likely will run out of residual before Southern Rust makes it to Hardin County.

Probably the second most important corn disease we see impacting yield is Grey Leaf Spot. Contrary to Southern Rust, Grey Leaf Spot does over­winter here, so the spores likely already are in your field on corn residue from previous years. These spores need humid, moist conditions to reproduce, and levels of infection will vary from field to field, so it is extremely important to scout each field when making the decision of whether or not to apply fungicide. A lot of hybrids also have a good deal of resistance bred in to them, so be sure to scout susceptible varieties first.

The bottom line – get out and scout your corn fields before making decisions regarding fungicide application. Fields that will be more likely to need a fungicide application are fields planted to a variety with low ratings of Grey Leaf Spot resistance, Irrigated fields, fields in areas that are prone to fog and heavy dew, such as creek and river bottoms and fields that are continuous corn. If you would like to learn more about corn diseases and fungicide application, contact the Hardin County Extension Service, or tune in to this week’s episode of Dirt 2 Dollars, where this week we will have Dr. Kiersten Wise, UK Extension Plant Pathologist to talk about corn diseases and fungicide application on corn. You can catch Dirt 2 Dollars at 8 a.m. every Saturday on ABE 93.7, or on Buzzsprout, Apple Podcasts, or just by “Googling” “Dirt 2 Dollars.” Each week’s episode usually is live by Wed­nes­day afternoon.

Matt Adams is a Hardin County Extension agent for agriculture and natural resources. He can be reached at 270-765-4121.