On Tuesday morning, Asian soybean rust was confirmed in three Louisiana parishes: West Baton Rouge, Pointe Coupee and East Carroll. A fourth find, in Iberville Parish, was confirmed Tuesday afternoon.
The Louisiana rust discoveries follow close behind those in neighboring Mississippi (see http://deltafarmpress.com/soybeans/soybean-rust-0817/) and Arkansas (see http://deltafarmpress.com/news/soybean-rust-0811/).
“In most cases, we’re finding rust in the classic areas: tree-lined where it stays shady and wet longer into the day,” says Clayton Hollier, LSU AgCenter plant pathologist. “The Iberville Parish find was just made this morning. It was on the edge of a field where Gramoxone had already been applied. Leaves had a few pustules — low incidence.”
The affected soybeans — all at R7, or later — are in commercial fields and past the point when rust can harm yield. Rust incidences in the fields range from 1 percent to 77 percent with severity ranging from 5 percent to 50 percent.
“The worst case, so far, is in Point Coupee Parish. It had a lot of pustules and was developing a lot of spores.”
Hollier is concerned for “some late-planted soybean fields in the state — still in the early reproductive stages — mostly planted behind wheat. Some fields are late because of replants, as well.
“The fields that really worry me are those at R3 to R5. There’s a lot of time left for development with those. Yield loss is still possible, whether from rust or other late-season diseases like the cercosporas, pod and stem blight, even aerial blight.”
While Louisiana is experiencing good growing conditions, it also has good conditions for disease development.
“We’re set up for disease problems. We’re having days that are overcast and somewhat rainy. The forecast is calling for 70 percent rain (through Aug. 21) and 60 percent for a few days after that.”
Growers with soybeans still in critical stages “must be aware of disease possibilities and protect against it as best they can.”
That could include a fungicide application, says Hollier.
“Growers with beans in the earlier reproductive stages with good yield potential need to consider a fungicide. Any crops later than that — especially in the R7/R8 stages — don’t bother with a fungicide. For those earlier stage beans, though, we’re looking at protection from the whole disease spectrum, not just rust.”
For a full accounting of 2009 U.S. rust finds, visit (www.sbrusa.net).
Soybean rust news can also be received through a Twitter account — http://twitter.com/beanrustinfo — that will be updated frequently.