Monitoring For Important Corn Diseases In 2023
DR. KIERSTEN WISE
PRINCETON, KENTUCKY
Farmers are annually concerned about corn disease, and this year will be no exception. Corn is moving through growth stages quickly, with much of the early April-planted corn approaching the ten-leaf stage, or V10. This growth stage has become a popular stage for a fungicide application timing with high-clearance ground sprayers, and there have been questions about what diseases are prevalent and how to monitor for disease presence to determine if a fungicide application is needed in 2023.
To date, weather across most of Kentucky has not been conducive for foliar disease development. Most of the state has experienced low rainfall and low humidity for several weeks, and this combination slows or prevents disease development. Even with spotty rainfall over the weekend, most areas will still be at reduced risk for foliar disease at this time.
This said, it is never too early to scout for disease and monitor your resources to determine where and when disease has been reported so you are ready for action, if needed.
One of the most important corn diseases to monitor in Kentucky is southern rust. The fungus that causes southern rust does not overwinter in Kentucky, but spores of the fungus move north on wind currents and weather each summer. You can track the movement of southern rust by watching the map on the cornipmpipe website here: https://corn.ipmpipe.org/southerncornrust/. On the map, red counties/parishes indicate that southern rust has been confirmed by university/Extension personnel. To date, no counties have confirmed southern rust that has been reported on the corn.ipmpipe, but I have heard from my Extension colleagues that the disease is likely in the Florida panhandle. Southern rust typically arrives in Kentucky in mid-July, and whether a fungicide will be needed to manage southern rust at that time will depend on the crop growth stage at the time it is detected in your area. Fungicide applications may be needed to manage southern rust through the milk (R3) growth stage. More information on southern rust can be found here: https://cropprotectionnetwork.org/publications/an-overview-of-southern-rust.
Another disease that can be monitored on the cornipmpipe website is tar spot. Tar spot is a new disease in Kentucky, with only two counties having confirmed disease in 2021 and one county with confirmed disease in 2023. In all cases, tar spot was not observed until mid-September and did not impact yield. This is a disease of concern in states to the north, and you can monitor real-time confirmations at https://corn.ipmpipe.org/tarspot/. No tar spot has been confirmed in the United States in 2023 to date. More information on tar spot can be found here: https://cropprotectionnetwork.org/publications/an-overview-of-tar-spot.
If considering a fungicide application in 2023, remember to scout fields first and check hybrid resistance ratings prior to fungicide application. Hybrids that are moderately resistant or resistant to foliar diseases (like gray leaf spot) are less likely to demonstrate an economic response to fungicide application.
Scouting over the next few weeks and just prior to tasseling can help determine if fungicide applications are needed. Although disease levels will continue to build over the course of the season, University research indicates that foliar fungicides applied at tasseling or early silking (VT-R1) provide optimal foliar disease control for diseases like gray leaf spot compared to applications that occur earlier or later in the season. For southern rust, a fungicide application may be needed through milk (R3). Management of tar spot will be on a case-by-case basis at this time. Always check with your county agent for updates on the diseases present in your specific county and for their help determining if management is warranted. ∆
DR. KIERSTEN WISE: Plant Pathology Extension Specialist, University of Kentucky