Soybean rust was found on leaves collected Sept. 5 in a Florence County, South Carolina, soybean sentinel plot, the USDA reported yesterday.

This is the third location and county in South Carolina known to be infected with rust this year; the 40th county in the U.S. Florence County is now the farthest north and east that soybean rust has been found this year.

Disease severity continues to increase at the Calhoun and Orangeburg County sites, South Carolina officials said today in the commentary on

One out of the 50 leaves was infected. They were collected from the MG V sentinel plots at the Pee Dee Research and Education Center in Florence County. On the infected leaf was one lesion which contained several very young sporulating pustules. No infected leaves were found in the adjacent MG 4 sentinel plots.

"Rust is probably present in South Carolina in more than just these three locations," officials said. Scouting of individual fields may be warranted. They report that most of the April-planted group 3, 4, and 5 soybeans are at or past R-7. 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.

Some important points to remember in making spray decisions are:

  • Soybeans that have not flowered do not need to be sprayed.

  • Soybeans that are at or past R6 should not be sprayed.

  • A strobilurin or fungicide combination containing a strobilurin should be sprayed if you want to control diseases in addition to rust.

  • The incidence of rust in South Carolina is still relatively low, but conditions are favorable for rust to spread within and between fields. If you are going to spray a fungicide in the next week, you need to include a strobilurin in the spray to optimize control of the most diseases possible. These sprays should be especially effective in high-yield potential soybeans with a full canopy that are R3 to mid R5 in growth stage.

  • SOURCE: South Carolina commentary on