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Corn+Soybean Digest

Asian Soy Rust Slow To Develop

Nearly a week after Asian soybean rust was located in south Louisiana and Alabama soybeans, the fungal disease hadn’t been found elsewhere. It was not from lack of looking, though.

“We’ve continued to scout and make (leaf) collections, but nothing has been found since the St. Martin Parish outbreak,” said Clayton Hollier, LSU AgCenter plant pathologist on June 12. “Having already found rust in south Louisiana kudzu, “my associate looked at several fields that Blaine Viator – a consultant who has helped us out a lot with rust monitoring – has maintained. She found rust in two of Viator’s sentinel plots.”

The south Louisiana rust was sporulating but, “thankfully, it was at very low levels of development.”

So far, June has largely been dry for Louisiana and that has helped keep the rust from spreading.

“We’ve had only scattered rains, including in south Louisiana. And the forecast for this area isn’t calling for any major rains for at least another week. Increasing temperatures may also be playing a role in keeping rust in check. We’re having highs in the low 90s.”

Hollier believes the pathogen is still active and a “strong, blowing storm” would likely move it outside current boundaries.

In Mississippi, the weather continues to be “kind of strange – we were very wet for so long and now we’ve switched off and are heading in the opposite direction,” says Tom Allen, assistant Extension/research professor at the Delta Research and Extension Center in Stoneville, MS.
“The southwestern part of Mississippi – Wilkinson County north to Natchez – is dry as is the southeastern part of the state. Smaller areas have gotten decent rains, mostly in patches across the north. Now, it’s heating up and weather is less conducive for rust. But it’s still out there and a threat.

“We’ve found nothing, though. We’ve been checking sentinels, kudzu and producer fields. It’s been so dry in places where we’ve traditionally found rust in the past. Before it turned off dry, though, we thought we’d find rust early.”

Have those charged with monitoring Midsouth rust had trouble with sentinel plots due to weather?

“We got our sentinel plots planted very early this year; the first week of March,” says Allen. “The majority of the plots – we planted an early Group 4, a late 4, a mid-5 and a 7 – are now flowering. We did lose two plots to flooding but we’re still at 21 sentinel plots throughout the state.”

In Arkansas, the wet weather “did cause some issues,” said Scott Monfort, Arkansas Extension plant pathologist on June 12. “To combat that we took a bit different approach with our sentinel plots.”

Instead of planting sentinel plots, county Extension agents “pointed out the earliest-planted soybean fields in the county. Those were marked and we’re now pulling samples out of them. As the season progresses and those fields mature, we’ll switch monitoring to younger beans. That way, we’ll continue to monitor beans that are in the peak period of rust susceptibility. We’ll see if that works a little better for us.”

Otherwise, the Arkansas monitoring program is the same. “We still have 26 or 27 county sentinel plots/fields we’re watching. There’s another 10-12 kudzu locations we check weekly.”

Could the late-planted Midsouth soybean crop be especially vulnerable to rust?

“Unfortunately, yes,” says Jeremy Ross, Arkansas Extension soybean specialist. “If we have some kind of weather event – a hurricane off the Gulf, or something – that pushes spores to us, we’re set up to have a rust problem with this late crop.

“But the deal with rust, as it has been for the last few years, is it is weather-dependent. Our hope is we’ll have a favorable late summer and fall for these late beans to develop and yield well. Of course, milder conditions are also more favorable for rust. Until it gets in the state, though, no one should be worrying about it. We’re very confident that we’ll be able to pick any rust up early and monitor its spread from there,” he says.

At this time of year, there’s usually a lot of talk about double-crop beans. “You’ll hear, ‘well, we only have about 300,000 acres of double-crop beans so there isn’t as much of a worry.’ But this rain has pushed us back a long way – probably a month,” says Monfort. “There’s probably 1 million, or so, acres in the state that will have been planted mid-May or later. We’ve got a tremendous amount of late beans.”

Coming into 2009, growers were warned that rust-monitoring funds were running low and programs were threatened.

“We had some remaining funds from last year – federal dollars – that we were allowed to carryover,” says Allen. “Thankfully, the Mississippi Soybean Promotion Board also came though and also funded the monitoring effort. We’re doing fine and running the same program we have been.”

All interviewed said funding for 2010 is still up in the air, however.

“We’ve been as frugal as possible,” says Hollier. “We’ll keep doing all we can for as long as we can to provide farmers with a warning system.”

Not finding rust early has helped keep expenses down, says Allen. “But the lateness of the bean crop – and the vulnerability to rust that brings – is a real concern. We’ll have beans planted into July, depending on location. That’s not a great situation since rust is usually found in July and August as we head towards harvest.”

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