Asian soybean rust has been found in sentinel-plot soybeans in Calhoun County South Carolina. This is the first rust in the state this year and the farthest north rust has been found in the U.S. in 2006.



There are now 35 counties in seven states that have had rust in 2006.



On www.sbrusa.net and in a more detailed South Carolina Soybean Rust Note e-mail to soybean specialists, South Carolina officials led by John Mueller, Extension soybean pathologist, Clemson University, reported the following this afternoon:



"Asian soybean rust was identified in samples collected last Thursday (Aug. 17) in Calhoun County from a field of Maturity Group V soybeans located near the intersection of State Road 22 and Interstate 26. This is the first identification of rust in South Carolina during the 2006 growing season.



"The plants were in a sentinel plot and were at growth stage R-5 (full size pods containing developing beans). Out of the 25 leaves examined, only one leaf exhibited rust. On that leaf was a lesion less than one-fourth inch in diameter which contained three very young pustules that had just begun sporulating.



"Immediately adjacent to this sentinel plot of MG V soybeans was a sentinel plot of MG IV soybeans. No rust was detected on the 25 leaves examined from that plot. The MG V plot exhibited very lush growth -- 40+ inches tall in 38-inch rows.



"To keep this find in perspective, you should be aware that last week I examined almost 1,400 leaves from 43 soybean fields or sentinel plots in South Carolina. One leaf exhibited the smallest detectable level of rust (one lesion or clump of pustules). Also remember that the closest field in Georgia with soybean rust is near Tifton (about 200 miles away).



"To determine the real extent of the infestation tomorrow (Tuesday, Aug. 22) Charles Davis and I will be collecting extensive samples from the monitoring plots, neighboring kudzu, and soybean fields throughout Calhoun County. We should have these results by late Thursday. We will tell you immediately if rust appears prevalent in the area.



"In the meantime, we are predicted to have slightly cooler temperatures and a fairly good chance of thunderstorms at least from now until Friday. This weather could be conducive to the development of rust and other pod, stem and leaf diseases, especially within a field.



Fungicide recommendations:



"At this time the levels of rust in South Carolina appear to be extremely low," Mueller said. "However, environmental conditions are favorable for rust and other diseases to develop.



"An application of a strobilurin to provide protection against rust and to help control other diseases is a good option for the next week. This is especially true for soybeans with a high yield potential that are between growth stages R3 and R5. At this time these soybeans show the highest potential for return from a fungicide application.



Soybeans that have not flowered do not need to be sprayed, Mueller said. Also, soybeans at late R5 or that are at or past R6 should not be sprayed.



"To control diseases in addition to rust, you must use a strobilurin or a combination product containing a strobilurin," he said.



Now that rust has been found in South Carolina, albeit at a very low incidence, scouting of individual fields may be warranted, the state commentary said. "However, the best indicator of rust in your area is still the nearest sentinel plot to your field."



The following South Carolina counties were sampled last week: Aiken, Allendale, Anderson, Bamberg, Barnwell, Calhoun, Colleton, Darlington, Florence, Hampton, Horry, Lee, Orangeburg, Sumter and Williamsburg counties.



Alabama says rust no longer visible in Montgomery County



In other USDA rust news today, Alabama set Montgomery County to "confirmed, destroyed" on the national observation map. Commentary said:



"Soybean rust can no longer be found on kudzu in the city of Montgomery. The disease had previously been detected on five kudzu patches in the downtown area where it had successfully overwintered. These patches have been monitored on a biweekly basis since they were first discovered in January. The disease has not been detected at these kudzu sites since early June. Central Alabama has experienced a severe drought for most of the growing season which likely had a direct impact on the pathogens ability to survive."



SOURCE: South Carolina and Alabama state commentaries on www.sbrusa.net; SC Soybean Rust Note e-mail, 8/21/2006.