August 2005
Soybean Rust Spreads in Baldwin County

Soybean rust was observed in a 60-acre commercial soybean field in Baldwin County on July 12. The field is approximately one mile northeast of the soybean sentinel plots that were observed to have rust on June 28 and whose rust has progressed in the meantime. According to Ed Sikora of Auburn University, the disease incidence within the field was estimated at 20 percent, with low disease severity. The field is estimated to be at the R4-R5 stage. “The field was sprayed with Stratego fungicide on June 26, two days before we detected extremely low levels of soybean rust in our sentinel plots,” Sikora said. His message continued: “Soybean rust has progressed in our sentinel plots. On June 28, we found symptoms of rust on one plant in each of the two sentinel plots (planted side-by-side about one month apart). On July 19, we estimated that the older of the two plots had 100 percent disease incidence, and the younger plot had 75 percent incidence. “We have not found rust on kudzu patches in the area, including patches located approximately half-way between the sentinel plots and the commercial field,” Sikora said. “I scouted three commercial soybean fields within 10 miles of the positive sentinel plot; all three fields were at the V2 growth stage. No rust was detected.” Soybeans are typically planted in late May or June in this county, Sikora said. The commercial field where rust was detected is uncommon as far as its advanced growth stage for this area. Growers with a crop between bloom (R1) and pod fill (R6) should consider applying a premix or tank mix of a strobilurin and triazole-type fungicide. An application at the R3 growth stage, regardless if rust is reported in the immediate area, would provide about three weeks protection against rust as well as reduce damage from Cercospora blight and frog-eye leaf spot.