From a distance, the Arkansas wheat crop looks great, lush. Get up close, though, and there are a handful of worrying diseases nibbling away.
“In some areas of the state, barley yellow dwarf is really bad — stunted plants all over fields,” says William Johnson, field sales agronomist with Pioneer. Johnson, speaking on a cell phone, is on his way to a Helena wheat field to check for diseases — a task he's far too familiar with lately.
“With barley yellow dwarf, there's some fall infection in our fields, but much of it looks like early-winter to spring infection. We just didn't have much of a winter. Since we didn't have a cold, nasty season, a lot of these aphids weren't killed off and they hung around all winter.
“This is disappointing and, unfortunately, it isn't just barley yellow dwarf. We're also seeing fields with rust and bad powdery mildew. That's seen in conjunction with wet, cool conditions like we've had the last couple of weeks.
“Wheat was going so well without problems. We were hoping to just skate through to harvest. Now, we're just hoping to hold on to the good yields we've got out there.”
In the fall, aphids usually vector the barley yellow dwarf virus to a wheat plant where it will multiply. Other aphids that feed on the infected plant can pick up the virus and transmit it to other plants.
The stunted patches now in evidence shouldn't be a surprise. Late last fall, the warning signs were everywhere.
“Unfortunately, what would be normally considered late-planted wheat runs the risk of barley yellow dwarf, too,” said Gene Milus last November. “The warm weather is really setting the virus up nicely.”
Milus, a University of Arkansas associate professor of plant pathology, continued: “Basically, if aphids come in at this time of year and they're carrying the virus, there's little question the virus will be established in a field. With such warm weather, the aphids will multiply and spread the virus. If you're seeing a lot of aphids, chances are the virus is being spread.
“You usually see patches of barley yellow dwarf in the field the following spring — the initial infection occurs in one spot and spreads from there. The plants in the center of those hot spots are more severely stunted than the ones at the outer edges.”
In the field
With Milus having foretold it, Brad Koen stands in a field outside DeWitt, Ark., looking at the predicted, stunted pockets of wheat. “Looks like a divot's been carved out of the field, doesn't it? Or maybe like a lightening strike.”
A consultant with Southern Agronomic Resources, Koen says the situation is worrisome. “I'll be honest: it isn't getting better,” he says. “And in addition to this, we're seeing septoria, leaf rust and some stripe rust. We could still have a great yield, but we've got to pay attention and not let these diseases get ahead of us.”
Farmers in the Grand Prairie, where 70-bushel wheat yields are the norm, tend to plant wheat very early and very thick, says Koen. Unfortunately, the earlier wheat is planted, the more likely is fall aphid infestation.
“And the thicker you plant, it seems the easier it is for the aphids to get down into wheat straw and bide their time during the winter. A lot of our wheat went in behind rice and was planted throughout September. We don't recommend planting wheat until October but some guys planted in early September. Those fields have been absolutely hammered.”
Koen hopes the barley yellow dwarf problems prove to be spring infection. “Spring infection normally doesn't cause near the stunting nor yield loss. We suspect the bigger yield losses happen with fall infection.”
In the fall, when the plant height is 4 to 6 inches, treatment levels are 50 aphids per linear foot of row. Last fall, Koen was seeing around 20 to 25 per foot.
“Those were moderate levels. Problem is, they were there all winter. Now, we're seeing a lot of damage because of that.”
Regarding leaf rust, Johnson says this is the “worst I've seen in over a decade. For the last 10 days, you can find leaf rust without looking hard. There had to be some leaf rust that overwintered. We've got leaf rust all the way up into northeast Arkansas on plants just starting to boot up.”
Earlier than normal
This year, Koen and his agronomist colleague, Curtis Fox, began seeing leaf rust and septoria earlier than normal.
“We were seeing a bit of everything around mid-March,” says Fox. “The pressure wasn't really bad, but it worried us, and we paid close attention. A couple of weeks ago, leaf rust began blowing up. We found stripe rust in a few fields, but it hasn't moved outside small areas of fields.”
Regardless, when boot split arrives, Koen says, wheat fields are treated with fungicides so plants get enough residual to carry the crop through.
Why treat? “Because producers are looking at good wheat prices,” says Koen. “Even most of our non-seed wheat acres are being treated. Rust is still low in the plants, but the crop looks so good with such good prices, farmers are more willing to spend on some insurance.”
When a wheat head starts emerging with leaf rust in evidence, the implications are bad, says Johnson. The plant throws all of its energy into reproduction and “from what I've seen, that's when rust diseases really get after a wheat plant. Perhaps that's because so much energy is placed in filling that head that the plant gives up some resistance. The diseases then get a toe-hold and take off.
“One of the bad signs is I'm finding leaf rust on varieties that, in the past, haven't had much trouble with the disease. That may point to another race shift.”
With lower prices, it wouldn't matter as much. But with barley yellow dwarf moving through $4-plus wheat, it's a question worth asking: is treating wheat seed with an insecticide worth the expense?
“This spring, producers who planted Gaucho-treated seed — and I've heard Cruiser worked as well — don't have nearly as many problems in their fields as do those to those who planted bare seed,” says Johnson. “The problem with seed treatments, of course, is expense. It isn't always cost-effective to treat wheat seed. But if we continue having these mild winters, I think if we're going to have good wheat, seed treatments are going to be considered more.”
Johnson isn't the only one who thinks so. Last fall, Troy Hornbeck — who manages the seed plant side of the Hornbeck Seed Company — decided to treat some AgriPro Savage wheat seed with Syngenta's Cruiser. Troy's brother, Jeff, who runs the farm side of their operation, then planted that seed.
“On our wheat fields with treated seed, the plant health is phenomenal,” says Troy. “It's so good, you won't believe it.”
Koen, who scouts Hornbeck's fields, agrees. “That's true. In the spring, when the wheat plants come up, the bottom leaves automatically begin dying off. With this wheat, though, the leaves have been alive from ground to plant top. These are the healthiest plants we've seen all over the county. We had some of the same varieties in nearby fields that didn't look nearly that good. The only thing that's different is the seed treatment.”
This is not definitive, however, since no checks were left in the field.
“We're going to repeat the experiment next year with checks,” says Troy. “This year, we used a standard rate of Cruiser on the seed. I don't know if Syngenta will go for this, but we'd like to try going with a low rate of Cruiser and see if we can control aphids for the short term. If using a lower rate will work, it'll save money and we can treat substantially more acreage.
“This isn't something to promote, we're not advocating it. But we are interested in seeing if it will work. If we can just put the aphids off a little while, it'll really help our wheat crop.”
The recent mild winters lead to another question: will recommendations for fall wheat planting have to be refigured?
“That's very possible,” says Koen. “But there's a problem with wheat planting. Farms continue to get bigger — producers have to get bigger to stay in business. These farms have gotten so big, though, that oftentimes producers can't wait for an optimum window to plant. Whenever the opportunity arrives, they plant the field.
“I still recommend not planting prior to Oct. 1. Early September wheat is a train wreck waiting to happen. It isn't just barley yellow dwarf — we had a couple of fields in Arkansas County that Hessian flies devastated. Those fields were planted in September and were so bad the producers didn't even fertilize the fields, they just disked them up.”
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