By Travis Faske, Extension Plant Pathologist
Southern rust was first detected in the 2017 cropping season on June 14 in Lincoln County. Since then it has been detected in ten other counties: Desha, Drew, Lonoke, Jackson, Jefferson, Perry, Phillips, Prairie, Pulaski, and Woodruff (Fig. 1). Due to cooler than normal temperatures in June southern rust development has been slow to moderate, but with warmer temperatures on the horizon, disease progress will likely pick up as it continues to spread northward across the state. Fungicide timing to protect yield potential is a critical decision for producers and consultants. Below are a few general guidelines on the benefit of a fungicide based on corn stages of growth.
Fungicides are effective at protecting corn yield potential, but given the price of corn many are considering the benefit of yield protection before applying a fungicide as an automatic treatment. The following table is a guideline on the potential yield protection provided by a fungicide at various growth stages with the assumption of southern rust being detected in the field and conditions favoring disease (80-90ºF and extended periods of dew or light rain) development are in the forecast (Table 1). See MP 154 for fungicides registered for use in Arkansas.