Soybean rust is continuing to develop and spread throughout much of the Arkansas Delta and is not showing any signs of slowing down, reports Scott Monfort, Arkansas Extension Plant Pathologist.

“The prolonged cool, cloudy, and wet conditions have allowed soybean rust to become very active and aggressive. This disease is more than likely in all soybean counties throughout the Delta and possibly the Arkansas River Valley. We are confident the disease will show up in many more soybean fields over the next week.

“For this reason, along with continued chances of rain and cloudy conditions in the state, we have made a few changes to our Soybean Rust Spray Advisory. We are strongly encouraging producers in all soybean growing counties in the state to consider treating soybeans in the R1 to mid-R5 with good yield potential for soybean rust. This year, soybean rust has proven to be more aggressive than in any other year since it first arrived into the U.S. and Arkansas.

“We would like to make a few added suggestions regarding our recommendations (see Arkansas Soybean Rust Update). For the soybeans fields sprayed at R2 to early R4 two to three weeks ago, please remember to scout the fields again (if below mid-R5) to determine if a second treatment is needed. We have observed several fields that needed to have the second application due to disease pressure.

“Producers should remember an application of a triazole or a mixture containing a triazole is needed once the disease is present in the field.

“Finally, they will need three to four hours of drying time for fungicides to be most effective, so try to wait until after the rainy conditions dissipate.”

“We would also recommend they use 10 gallons of water by plane and 15 gallons by ground in the application, if possible. This will ensure they have adequate coverage of the fungicide throughout the canopy.

“They should be sure to determine the growth stage and yield potential of their fields before applying a fungicide.”

Craighead, Jackson, and Lawrence counties are the latest counties confirmed with soybean rust. This makes a total of 21 counties confirmed with soybean rust (Arkansas, Ashley, Chicot, Craighead, Crittenden, Cross, Desha, Drew, Jackson, Jefferson, Lawrence, Lee, Lincoln, Lonoke, Monroe, Phillips, Poinsett, Prairie, Pulaski, St. Francis, and Woodruff).

For the latest Arkansas report and recommendations, go to Arkansas Soybean Rust Update.

smonfort@uaex.edu