FROM: John Mueller, Extension Soybean Pathologist, Edisto Research and Education Center
Both Joe Varn and I (he was first) have found soybean rust in Barnwell County in the last few days.
SOYBEAN RUST HAS NOW BEEN FOUND IN COLLETON, BAMBERG, BARNWELL AND ORANGEBURG COUNTIES.
Counties that have been surveyed but no rust found now include: Allendale, Anderson, Calhoun, Clarendon, Dillon, Darlington, Dorchester, Hampton, Horry, Jasper, Lee, Marion, Newberry, Richland, Saluda and Sumter Counties.
Here are the survey results from the last week:
Justin Ballew, Horticulture and Agronomy Agent for Dillon and Marlboro Counties collected leaves from 3 fields in Dillon County on September 27th. He looked at a total of 150 leaves from the 3 fields but could find no rust.
Jonathan Croft, Orangeburg County Agronomic Row Crop Agent collected 80 leaves from a field of R-6 soybeans in Dorchester County on September 27 but could find no rust.
Joe Varn, Bamberg/Barnwell Agronomic Agent found rust in 4 of 65 leaves collected on October 3rd from a field located on Highway 278 just southeast of Barnwell. He also found rust in 3 of 45 leaves collected October 3rd from a field on Highway 3 approximately 5 miles north of Blackville. In both fields only a few pustules were present on each leaf. On the same day he collected leaves from a field on 278 west of Barnwell but found no rust.
With the help of my technician, Bill Bonnette, we collected leaves on October 5th from a fungicide trial on the Edisto REC. The field was in late R-5 growth stage. We examined 25 leaves from each plot. Rust was found on leaves from 3 of the 4 non-sprayed plots. Two of the plots had rust on 1/25 leaves and the third plot had rust on 4/25 leaves. Rust was very low, just one pustule per leaf on all but 1 of the leaves. On that leaf there was a colony of rust about 1/5 the size of a dime. In the 8 fungicide treated plots rust was found on leaves in 2 of the plots. In both of those plots only 1 leaf out of 25 had rust present. Again it was only 1 or 2 pustules per leaf. This means that 198 of 200 leaves were clean.
So, a very low level of rust is scattered throughout some of our fields in the Savannah Valley. Probably the only field we have found that had rust at levels that could cause a yield loss was the original find in Colleton County. In the fields we just found in Barnwell County it will be 2 to 3 weeks before rust will build to levels that could cause some yield loss. By that time these fields will be rapidly approaching defoliation, especially if we get cooler weather after Hurricane Matthew.
Although our sampling has been somewhat limited, we have no evidence to suggest rust is present north of the Santee/Cooper area or in the Anderson area.
Most of our soybeans are too far along to spray with a fungicide but it seems that once again this year we have avoided significant damage from Soybean Rust.
If you would like an update on the occurrence of soybean rust across the United States check out http://sbr.ipmpipe.org .