As The Winds Blow
Rust Ready Report
September 11, 2008
Kudzu in Louisiana is small but mighty. Compared to Alabama, Georgia, and Mississippi, the Bayou state doesn’t have a lot of the pesky plant. But when Asian soybean rust gets into Louisiana kudzu, the implications go far beyond the state’s borders.
This is primarily because the wind patterns coming out of Louisiana travel up the Mississippi River Basin and the Ohio River Valley, moving along the way into the areas where much of the country’s soybeans are grown. Asian soybean rust loves to travel by air, often hitchhiking on raindrops — which is what happened late last season when rust scattered deeper into soybean strongholds than ever before.
So when soybean rust was spotted in a kudzu patch in south-central Louisiana on May 8 — a full 53 days earlier than at the same site in 2006 — retailers and growers in the nation’s midsection took notice.
“Just a few leaves were infected in a fairly compact area in New Iberia,” says Clayton Hollier, Louisiana State University (LSU) AgCenter plant pathologist. A routine check of the area, an apartment complex drainage ditch covered with kudzu, resulted in the May 8 discovery.
Hollier and his LSU colleagues are very aware of the potential impact of any soybean rust found in Louisiana. “We feel a sense of responsibility for our own growers and those outside our state borders,” he says. “We know that what’s going on in Louisiana is of interest to them, so we will get the information out quickly. We want them to know that as soon as we know there’s rust, they will know so that they can make the very best decisions possible for their own situation.”
This is the second year straight that this particular kudzu patch was infected by Asian soybean rust. “It brings up another question: Did it overwinter there?” Hollier asks. Routine checks of the areas where rust developed in the state last year were conducted, along with some new areas. “We wanted to check for its survival and ability to move.”
The LSU AgCenter has just started greenhouse studies to see if soybean rust is overwintering on stem tissue. “All the leaves were killed back by frost this winter, so it could be lower in the canopy,” he says.
The study results could help Louisiana soybean growers adjust their agronomic practices to catch rust as early as possible. The preventive fungicide applications that the region’s growers have historically used for other diseases have proven successful against rust thus far. “Last year, growers added product to their fungicide application to control rust and actually controlled it very well,” he says. “While it was widespread, we didn’t get the explosion that would have happened without the applications.”
According to Hollier, soybean yield loss in the areas where rust occurred was around 1%. “Without the preventative fungicide applications, it probably would have been in the 7% to 8% range,” he says.
Domark, Stratego OK’d
The list of Asian soybean rust- approved fungicides keeps getting longer. EPA has awarded full Section 3 approval to Stratego from Bayer CropScience and Domark 230, manufactured by Isagro and distributed by Valent U.S.A. Corp.
Both had previously received Section 18 Emergency Exemptions for use in soybeans for Asian soybean rust. They also are approved for a number of other soybean diseases.
Stratego can be used as part of Bayer CropScience’s Plant Health program to improve overall crop health and increase yield potential. A premix of strobilurin and triazole chemistries, its two different modes of action inhibit spore germination on the plant surface and fungal growth within plant tissues.
Domark 230, which contains the active ingredient tetraconazole, can be used as both a preventative and curative treatment for soybean diseases, protecting existing and new growth.
It will help growers achieve Maximum Harvest Value, a combination of disease protection, ease of harvest, and crop safety to maximize yields, according to Valent.