Asian soybean rust has now reached Tulsa, Okla., the farthest north it has traveled in 2007. The fungal disease isn't through with the Mid-South, however. The second week of August saw six new ASR finds in Louisiana and one in Mississippi, a Pearl River County sentinel plot.
With fresh finds in Jefferson Davis, Allen, Evangeline, Concordia, East Baton Rouge and Bossier parishes, David Lanclos, LSU AgCenter soybean specialist, has “already had calls on what should be done. Most of the questions are late-season concerns and coming from growers who have soybeans approaching R-5, or have just made it to that stage. They're wondering about a fungicide.”
At this point, a lot of Louisiana soybeans have been desiccated, are shelling easily in hand and are showing excellent quality.
“I'm not recommending everyone go out and apply a fungicide mix at R-5, but we are seeing some quality differences in beans that had a strobilurin applied.”
Some of the new Louisiana discoveries were in sentinel plots, others in production fields. ASR is being found in the tops of plants and usually when that's the case, “the severity is typically at 30 percent to 40 percent, at least.”
An interesting piece to the ASR puzzle involves how the disease responds to Mid-South weather. “We've been trying to educate growers and consultants about how heat and ASR interact. You know, ‘once it gets above X temperature, the disease really slows down.’
“Definite answers are elusive. If you go back and look at the conditions in 2006, we had nowhere near the moisture levels we've got at the end of this season.
“Obviously, wind patterns are a huge deal in ASR movement. That's obvious in the current situation in Oklahoma. Will ASR move farther north from Tulsa and yet never hit the eastern side of the country? That's something to watch.”
How much of Louisiana's soybean crop is mature enough for ASR not to be a bother? “Right now, we're probably 50 to 60 percent out of the woods. Late wheat-beans are the major worry. But a lot of the wheat-beans are approaching R-5.”
Agriculture economist Bob Stark recently checked the costs of fungicide applications. The impetus behind his study was the discovery of ASR in southwest Arkansas (now in Little River, Hempstead, Lafayette and Miller counties).
“The cost of production budgets for this year were developed last fall,” says the Arkansas Extension economist and associate professor of agriculture at the University of Arkansas-Monticello. “I was interested in touching base with some suppliers to see where we are with the prices that had been plugged into the budgets last fall.”
Caution: the numbers Starks cites are based only on suppliers in southeast Arkansas. Arkansas Extension plant pathologists are recommending that soybeans in southwest Arkansas be sprayed if plants are at R-1 to R-6.
“Spraying should only be from Clark County south to Magnolia, Ark., and west to the Texas/Oklahoma borders. If the fields are R-1 to R-4, they should get a combination of a triazole and a strobilurin. Any beans that are late R-4 to R-6 should receive only a triazole.”
Two strobilurins — Quadris and Headline — have been recommended, both at a 6-ounce rate. Starks says an application will run growers about $11 per acre.
“One thing I want to emphasize is these are average costs. Individual producers may be able to find slightly lower or slightly higher costs. It depends on the supplier and other factors.”
Among triazoles, there are several recommended, “including Folicur at 4 ounces, Laredo at 5 ounces and Domark at 5 ounces. I'm not endorsing only those three — they're the only ones I could get prices on. There are others that plant pathologists are happy with. Regardless, those three triazoles will cost about $7.50, maybe a bit more.”
As for application costs, “I was given quotes based on 5 gallons of water per acre. The average cost was $4.25 per acre for aerial application. If you're using a tank mixture of a strobilurin and a triazole, you're looking at spending somewhere around $23 to $24 per application.”
After putting the numbers together, “plant pathologists told me 10 gallons of water per acre is better. That means there may be additional aerial application charges.”