Soybean growers in the Carolinas and Virginia will get an early visit from Asian soybean rust, apparently thanks to a storm spun from Hurricane Isaac.

The disease was found last week in Barnwell County, S.C., and this week in Robeson County, N.C.

This is particularly alarming because Asian soybean rust has never been found this early in North Carolina, says long-time North Carolina State University Soybean Specialist Jim Dunphy

Dunphy says soybean rust was detected in soybean in Robeson County, near St. Pauls, N.C., on Sept. 11 and in Johnston County today. This is the earliest soybean rust has been detected in North Carolina. 

Rust was identified on one of four leaves brought to the lab. The earliest detection of soybean rust in North Carolina in previous years was Sept. 15 in 2007, he says.          

Full season soybeans that have just reached full bloom (stage R2) typically have 65 days until they’re safe from rust or frost (stage R7) or closer to 55 days for double crop beans.

If soybeans have small pods in the top of the plants (stage R3), they have 55 and 47 days, respectively, to R7. With full sized pods in the top of the plants (stage R4), they have 45 and 38 days, respectively, until R7. 

From stage R5 (small seeds in the top of the plant) they typically have 35 and 30 days, respectively. From stage R6 (full sized seeds in the top of the plants), they typically have 20 and 17 days, respectively.

Rust will typically take 10-20 days from initial infection to develop to detectable levels. It will take another 7-14 days to spread to other leaves on the same plant, and another 10 days to cause significant defoliation.