Asian soybean rust continues to spread across Louisiana, so far no yield threat

Linda Benedict, Hollier, Clayton A.  |  8/19/2009 1:29:53 AM

News Release Distributed 08/18/09

The discovery of Asian soybean rust in a soybean field in Iberville Parish on Aug. 18 was the latest of four finds of this potentially serious disease over two days in Louisiana.

So far, the finds are in soybean plants that have already formed the beans and are nearing harvest, making them immune to any yield damage that could be caused by the disease, said Clayton Hollier, LSU AgCenter extension plant pathologist.

The other three recent discoveries were in West Baton Rouge, Pointe Coupee and East Carroll parishes, Hollier said.

All told, Asian soybean rust has been found in 14 parishes across the state in 2009, mostly in kudzu but also in soybeans.

“What’s of concern now are the soybeans out there that were planted late – mostly after wheat harvest – that are in the pod-forming stages (R3 to R5),” Hollier said. “These fields should be treated as soon as possible, if good yield potential exists.”

The treatment for Asian soybean rust and other late-season diseases is fungicides. Hollier said a number of options are available, and farmers need to check with their local parish LSU AgCenter extension agents for their recommendations.

“We’re a little ahead this year than we have been in the past,” Hollier said, meaning that more rust was found this year than since the disease was first discovered in Louisiana in late 2004.

Asian soybean rust is a disease that dries up a plant rapidly and spreads quickly so it can and has destroyed much soybean acreage in other countries, mostly in Africa and South America.

“We found a lot in kudzu early on – more than usual,” Hollier said. “But then it got dry. Now with the rains coming back, we’re finding more.”

Kudzu serves as a host plant for Asian soybean rust, allowing it to overwinter in states in the Deep South, including Louisiana. Extremely cold weather might kill the spores that cause this disease.

Hollier suspects that his associate, Patricia Bollich, who serves as the state’s chief scout for the disease, will be finding more in the next few days as she travels around the state.

“As long as farmers treat the fields that are still vulnerable to the disease, we should have no problem managing the disease this year,” Hollier said.

He said Midwestern soybean farmers are concerned about the finds of Asian soybean rust in southern Arkansas, Mississippi and Louisiana, with the tropical storm and hurricane season starting to get into gear. The concern is that the winds will blow the spores north.

“I’m sure soybean farmers in the Midwest are beginning to scout their soybean fields to determine the need for fungicides,” Hollier said.

To reduce problems with Asian soybean rust, it’s best to plant soybeans in Louisiana on time in the spring. But sometimes weather – either too wet or too dry – can delay the planting of soybeans. Also, some farmers double-crop soybeans with wheat so get a late start planting soybeans after they’ve harvested their wheat.

“Weather conditions currently favor Asian soybean rust development,” Hollier said.

Linda Foster Benedict

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