Preparing Western Kentucky For Southern Rust In Corn

DR. KIERSTEN WISE 

PRINCETON, KENTUCKY

Western Kentucky will receive rainfall from tropical storm Beryl this week, and there are concerns that this storm will bring with it an unwanted disease, southern rust of corn, caused by the fungus Puccinia polysora. This fungus does not overwinter in Kentucky, and spores blow north each year on wind and storms.

Current Status

The disease has developed slowly in southern states this year, but has been confirmed in Texas, Louisiana, and southern Arkansas, as well as Georgia, so far. Confirmed disease can be observed on the cornipmpipe website. On the map, red counties/parishes indicate that southern rust has been confirmed by university/Extension personnel. The track of the tropical storm skirts most areas with confirmed disease, so it is not expected that large amounts of spores will move north on the storm. There would also need to be favorable conditions for disease to develop if spores are deposited in western Kentucky. Southern rust in Kentucky is typically confirmed in mid-July each year, depending on weather conditions, so if southern rust is observed in the coming weeks, it would not be abnormal. If southern rust is suspected, the fastest way to get a diagnosis through the Plant Disease Diagnostic Laboratory (PDDL) is to submit samples through county agents.

Scouting

It will be important to scout and monitor fields over the next few weeks and submit samples to the PDDL through local county Extension agents if you suspect southern rust in a field. Tips on identifying southern rust can be read in a previous article.

Potential Impact & Fungicides

The potential impact of southern rust in Kentucky will depend on the crop growth stage of a field once southern rust is confirmed in an area. Previous research from southern states indicates that fungicides may be needed to protect yield while corn is in the tasseling through milk (VT-R3) growth stages. Once corn is past milk (R3), fungicides are not likely needed to manage the disease. If fields have already received or will soon receive a fungicide application this year at tasseling/silking (VT/R1), they are not likely to need a second application of fungicide once corn reaches the blister (R2) growth stage. For areas where planting was significantly delayed, careful scouting and monitoring for disease presence is key to determining if or when a fungicide will be needed for southern rust management.  

Additional Information

More information on timing of fungicide applications for southern rust can be found in Table 2 of the Crop Protection Network publication on Southern Rust. The efficacy of specific fungicide products for southern rust are described in the updated fungicide efficacy table for management of corn diseases, which is developed by the national Corn Disease Working Group. ∆

DR. KIERSTEN WISE: University of Kentucky