Like a party-crasher who shows up five minutes before everyone goes home, the late-season rush of new Asian soybean rust cases is annoying but can do little damage. Pods are made, leaves have dried down and the Southern soybean crop is nearly all in the bin.
Confirmed on Nov. 18, a Kentucky kudzu leaf is the latest rust discovery — the furthest north yet. “Lesions with pustules were found on a very small section of one leaf out of perhaps 75 collected,” wrote Don Hershman, Kentucky Extension plant pathologist, on USDA's soybean rust Web site. “That kudzu patch has been killed back by the cold temperatures, so we probably no longer have soybean rust in Kentucky. So much for our ‘epidemic’ in 2005.”
While no more problematic for their crops, the Carolinas have seen a steady stream of rust confirmations over the last few weeks.
“We picked up rust for the first time on Oct. 28,” said James Dunphy, North Carolina Extension soybean specialist. “It's now in 18 counties (Greene, Pitt, Lenoir, Hoke, Carteret, Craven, Brunswick, Bladen, Columbus, Onslow, Robeson, Pender, Scotland, Duplin, Hyde, Catawaba, Edgecombe and Tyrrell). All but two of the counties are contiguous.”
Twenty-two counties have been found to harbor rust in South Carolina: Barnwell, Calhoun, Horry, Pickens, Allendale, Georgetown, Orangeburg, Anderson, Oconee, Darlington, Bamberg, Saluda, Lexington, Edgefield, Newberry, Dillon, Aiken, Clarendon, Colleton, Greenville, Lee and Marlboro.
“Most of the incidences we've found are from samples Extension agents have sent in,” said John Mueller, South Carolina Extension plant pathologist with Clemson University. “Most are low-level infections. We usually check 20 or 30 leaves per location and we'll find one or two with a few pustules.
“It's important we record the different counties where rust is found so growers have a feel for how widespread this has become.
“And we must consider what could have been without the drought in September. Rust could have been as widespread earlier and been very damaging. It's a warning for next year.”
Dunphy agrees that drought in the Carolinas likely held back a more rapid advancement of rust. “Our really early beans did well. Once we got into the conventional maturities, however, we began seeing the effects of the dry weather and yields dropped off fast.”
Many areas of North Carolina were wet during the planting season. Then conditions turned very dry. Many producers are now 10 to 12 inches behind normal rainfall.
“In the eastern part of the state, we had some weather damage problems — probably from Hurricane Ophelia and the 10 days following. During that time, it stayed cloudy and humid, the kind of conditions many soybean diseases like. That led to serious quality problems on top of lower yields.”
Once North Carolina producers began harvesting late-maturing varieties, quality wasn't as bad but the low yields, as a consequence of dry weather, remained. Typically a late-harvesting state, North Carolina is less than half done with harvest.
“We should be finished with harvest in mid to late December,” said Dunphy. “We'll probably end up with an average crop. It certainly won't be a special crop and won't be nearly as good as it looked in August. We tend to run in the high 20-bushel to low 30-bushel range. I think we'll be in the 20s this year.”
South Carolina is close to being finished with harvest — probably 80 percent done, said Mueller. Despite the drought, “there are still some good beans out there. Some growers are reporting yields in the high 30s and 40s.
“For other fields, the drought hit at the wrong time. Yields there are pretty poor. There are parts of the state hit with drought for nearly the whole year. Many of the soybeans in those areas were abandoned.”
Through the growing season, Mueller took “plenty” of calls about Asian soybean rust. “A lot of people in this state were watching closely.”
In the southern part of South Carolina, “quite a few acres were sprayed with fungicides in early August. At that time, we had an excellent crop and growers sprayed not only to protect against rust but also pod and stem blight and anthracnose.”
However, once drought hit there was less need to spray. “By the time we waited it out, it was too late to help the first crop,” said Mueller. “And the second crop wasn't very good and rust had slowed so it wasn't worth the spraying cost.”
Neither specialist believes soybean rust impacted yields.
“I don't think rust caused any economic damage to our crop,” said Dunphy. “The majority of the finds have yielded a very limited number of pustules on a small percentage of leaves detectable only under a microscope. From that stage to widespread damage in a field, you're looking at two weeks.
“Well, by the time we found the first rust, 80 percent of our soybeans had already dropped their leaves. Add several weeks to that and we didn't have any (pod-fill) going on. That's why I don't think this year's rust cost us much, if anything.”
As in other states, North Carolina had a soybean rust monitoring plan in place prior to the season. “We had 26 sentinel plots scattered throughout the state,” said Dunphy. “We had a sentinel plot in, roughly, every third county along the South Carolina line and up the coast to the border with Virginia.
“We tried to extensively cover the South Carolina line and the coast, focusing on early detection, not so much late. The primary purpose of that, of course, was to give our farmers ample warning if the rust was coming close.”
The best guess is soybean rust was distributed in North Carolina by Hurricane Ophelia. The first 13 rust sites — as well as the find in Edgecomb County, northeast of Raleigh — fit that theory.
As for the 15th find — Catawaba County, northwest of Charlotte — “we're not sure exactly how rust found it.”
Dunphy and colleagues are now concentrating on soybean plants that refuse to dry down. There are also plants to check under night lights. “Those stay green until frost kills them. Last year, several states — including Missouri — found soybean rust on plants under night lights. Everything we're looking at currently is an unusual plant.”
North Carolina has about 1.5 million acres of soybeans. “There's a heavier concentration in the Coastal Plain and Blacklands than in the Piedmont, although there are plenty of beans in the Piedmont.”
Of the state's beans, just short of half are double-cropped and almost all are dryland. “Typically, our soybeans are heavily no-till and narrow-row,” said Dunphy. “That's especially true for the double-crop beans.
“Most of our acres weren't sprayed with a fungicide — less than half, I'm sure. We usually have scattered acreage sprayed with a fungicide but we don't normally spray for diseases like the Mid-South does.”
How do the Carolina specialists see soybean rust developing next year?
“It's a bit of guessing game,” said Dunphy. “I think farmers will remain very concerned. We now know this disease can get to North Carolina and develop enough to be detectable here. There's no reason to think it can't develop enough to cause damage if it comes early enough.”
Starting in February, Mueller will be “watching Florida to see what kind of winter they have. If it's mild, we'd anticipate seeing rust earlier next season.
“The big difference for next year is one wouldn't anticipate the kind of drought Texas, Louisiana and Arkansas had in 2005. So I think we should watch for rust not only coming up from Florida but also from the lower Mississippi valley. That would be a totally different situation than we saw this year. The potential for more rust is definitely there.”
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