Finding cool, wet October weather to its liking, Asian soybean rust is stretching its legs. At presstime, the fungal disease had been confirmed in 227 counties in 15 states with new counties added to the infected list every day.
The disease has recently traveled steadily northward from Louisiana up the Mississippi River into the Bootheel and west Tennessee. While the Mid-South soybean crop is long finished and ASR's arrival is too late to damage yields, Extension researchers have been tracking it closely.
“If you look at the wind currents and where ASR has been found, there's little doubt Louisiana is the original source,” says David Lanclos, LSU AgCenter soybean specialist. “It's just been waiting for a chance to move. The weather has helped and having combines blowing spores out the back certainly has to help a wind-borne organism.”
Even with heat, drought and a docile ASR in Louisiana during the growing season, Lanclos expects a record soybean yield for the state.
“That's rather amazing. Our very last Group 5s are being cut now. And keep in mind that we've had to abandon something like 35,000 acres — mostly to drought in Catahoula and Concordia parishes.”
The rust was found in southeast Missouri in mid-October.
“Almost all areas where we've pulled green leaves, we're finding ASR,” says Al Wrather, Missouri Extension plant pathologist. “It is simple to find but it's no threat to crops and it will die off when freezes hit.”
In the meantime, Wrather says, this is a chance to educate regional Extension agronomists and crop consultants about the disease.
“Eventually this disease will arrive during soybeans' vulnerable stages. When that happens, it's best everyone knows what it looks like in the real world. We're taking advantage of this opportunity.”
By the time ASR was confirmed in northwest Tennessee in mid-October, “most of our crop had been harvested or was defoliated,” says Angela Thompson, Tennessee Extension soybean specialist. “If ASR continues to come into the state, it's not that big a concern. Our Group 2s, 3s and many of our Group 4s have already been harvested or are on the brink of harvest. The Group 5s and wheat-beans are still in the field, but those have mature pods and are defoliating. We'd never recommend a fungicide this late.”
Scouts are currently checking middle Tennessee and as far into east Tennessee as possible.
“Extension agents say they've had very few calls from producers on this,” says Thompson. “That's probably because, since ASR was confirmed in Kentucky earlier, (producers) assumed it was already in Tennessee somewhere.”
ASR has spread rapidly through the Arkansas Delta.
“We're closing in on 30 counties infected,” says Trey Reaper, Arkansas Extension soybean verification program coordinator. “An oddball outlier is Washington County, up in the northwest corner of the state. ASR was found on the research station in Fayetteville. Another outlier is Faulkner County in the central part of the state.”
ASR has yet to be found in southwest Arkansas. “That kind of surprises me,” says Cliff Coker, Arkansas Extension plant pathologist. “But, as we keep checking, I suspect we'll find it.”
Coker says the disease will probably be a real problem for farmers once a decade. “Both times it's shown up in Arkansas have been well after the crop is finished.”
Billy Moore, Mississippi Extension plant pathologist, agrees with Coker.
“I believe if rust ever becomes a real problem during the season, everything will have to come together just right — warm winter, big inoculum load, a cool, wet growing season, etc.,” says Moore, who leads Mississippi's ASR scouting effort. “How often does that happen? This isn't a disease we'll have to fight year after year. But while it may be a rarity, we must be prepared when it does hit. Let's not underestimate ASR's ability to wreak havoc in our soybeans.”
Moore was in northeast Mississippi on Oct. 25. The farmers there are harvesting beans “in a big way. I didn't realize we still had some bean acreage left to bring in. But Mississippi's crop is well over 90 percent harvested.
“There are a few green patches of beans left — particularly where there's been stink bug damage. We're still checking those and some rust was found near Verona yesterday. ASR was found near Stoneville, too.”
All those interviewed have a harsh winter on their wish list.