As of early February, soybean rust has been found at 12 locations in eight Louisiana parishes. The early year finds are not unprecedented. However, the severity of the disease in some of the locations is.
“We’ve found rust in early January before – but never at this level. We need people to know about this and help us follow the progression of this, if possible,” says Clayton Hollier, LSU AgCenter plant pathologist. “The more people that know about this and are watching out for it, the better.”
Hollier’s associate, Patricia Bollich, found soybean rust for the first time this year on Jan. 2. It was on kudzu in Baton Rouge.
Bollich then began looking at other kudzu sites to see what might have survived the, “very minor winter,” says Hollier. “It’s been warm, so far. She then began finding, even in areas mostly dead patches of kudzu, there would be a survivor or growth on the plant.”
Those new leaves were infected. “That seemed odd because the kudzu leaves were the size of a quarter. And those leaves had pustules producing spores.
“We’ve now found rust on kudzu in eight parishes, mostly along the coast. In one parish, the disease was found on volunteer soybeans about 6 inches tall.
What might this portend?
“If the warm winter continues and we don’t get a killing freeze, innoculum will be building far earlier than normal,” says Hollier. “There will be more innoculum out there when soybeans are planted. That’s a big concern – we don’t want that for the growers.
“But at the current rate, if the innoculum continues to spread as quickly as it has been, then concerns are warranted. It worries me that this disease is building up just as the kudzu is sprouting, growing and developing due to the mild winter.”
That doesn’t mean Hollier is close to panic. “We just want growers, Extension agents and consultants to know this is out there more than we’ve seen before.”
There are also reports from Alabama and Georgia that rust has been found early in 2013.
“This rust is surviving winters and showing up early,” says Hollier. “We believe the survival is local – I’ve suspected that for years. What’s happening this year, with very young plants being infected so early in development, lends itself to backing that belief.”
The range of infection is broad.
At some of the sites that Bollich typically checks, “she’s finding only a few pustules on a few leaves. In other cases, though, leaves are just covered with pustules.”
On those worst-infected plants, “you can literally hold a leaf in your hand, point with a pencil, and you’ll hit a rust pustule. It’s that severe.”
Hollier is holding out hope for a south Louisiana freeze. “It’s only early February. To have a freeze between now and the start of the growing season would be the norm.
“The current warm winter follows last year’s mild winter. Those types of conditions back-to-back, I think, has allowed the build-up of rust.”
As the situation progresses, Hollier and colleagues will keep producers updated. “Remember, all the parishes we’ve found this in are coastal except for Lafayette Parish – which is very close to the coast – and East Baton Rouge Parish. Baton Rouge is as far north as the rust has been confirmed, so far.
“There have been some freezes and heavy frost in the northern half of the state. We have not surveyed for the rust above mid-state.”