Asian soybean rust was confirmed on soybeans in two more South Carolina counties Friday, including one in Sumter with the highest initial severity found to date in the state.

Both finds, in Sumter and Hampton counties, were in soybean sentinel plots. South Carolina has five positive counties. The U.S. now has 45 rust-positive counties and parishes, with eight of those reported in the past four days.

The South Carolina commentary on said:

"Rust was identified yesterday (9/7) in samples collected from the Maturity Group 4 sentinel plots near Estill in Hampton County. Rust was present on one leaf out of 60 collected by Tommy Walker yesterday morning. Infection severity was very low, with just two pustules in one lesion. Leaves from the Maturity Group 5 sentinel plots in Hampton County were not examined.

"Rust was identified this morning (9/8) in samples collected on Sept. 6 from the Maturity Group 5 sentinel plots off of Highway 521 South near the Sumter/Clarendon County line in Sumter County. The samples collected by Greg Harvey exhibited the highest initial levels of severity of any of our rust finds," the commentary said.

"Seven out of 50 leaves had rust present. Two of the leaves had greater than 50 pustules per leaf, one of the leaves had 20+ pustules, and the remaining four leaves had five to 10 pustules per leaf. No rust was seen in the Maturity Group 4 sentinel plots in Sumter.

In chronological order, rust has now been identified in Calhoun, Orangeburg, Florence, Hampton, and Sumter counties this growing season. All finds were in the sentinel plots sponsored by USDA/APHIS.

Growers told to spray, depending on growth stage, yield potential

"Growers throughout the state with soybeans in growth stages R3, R4, and early- to mid-R5 should be spraying a strobilurin or combination fungicide containing a strobilurin in fields with yield potentials exceeding 35 bushels per acres," SC officials said.

"Growers in the immediate vicinity (a 25-mile radius) of the Sumter County site should strongly consider spraying a combination fungicide, strobilurin + triazole, to get the eradicant action of the triazole, since this infestation seems more advanced."

As of 9/8, most of the April-planted group 3, 4, and 5 soybeans are at or past R-7, the commentary said. Most of the May-planted Group 6,7 and 8 soybeans are at R5. Only a few fields planted in June have not yet flowered. All of the fields at R6 or later are past the stage at which they can be damaged by rust or be sprayed with fungicides.

SOURCE: South Carolina commentary on