Soybean rust was detected in soybean in Robeson County near St. Pauls, North Carolina, today.
This is the earliest that 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 September 15th in 2007.
Soybeans that have just reached full bloom (stage R2) typically have 65 days until they’re safe from rust or frost (stage R7) if they are full-season soybeans, or closer to 55 days if they are double-crop soybeans. If they 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. This assumes optimal conditions for rust “65-85 degrees, and either overcast or rainfall through much of this period.
This is not common in North Carolina in September and October but has and can occur.