Clayton Hollier, Benedict, Linda F. | 6/28/2007 7:12:42 PM
Asian soybean rust was observed in both Avoyelles and Rapides parishes on Wednesday (June 20) and confirmed by LSU AgCenter scientists on Thursday (June 21).
"The significance of this sighting is that it is the first observation of Asian soybean rust on soybeans in Louisiana during the 2007 growing season," said Clayton Hollier, LSU AgCenter plant pathologist.
The finds were each in a sentinel plot in the two parishes, Hollier said. Soybean sentinel plots are planted just ahead of commercial beans to serve as an indicator of the rust disease, Hollier said.
"If Asian soybean rust is found in a sentinel plot, then the plot has served notice that the disease is in the area," Hollier said. "This means we have to intensify our scouting for the disease and that management practices should be considered."
Asian soybean rust is one of the most devastating of the diseases to affect soybeans because it can spread so quickly and do so much damage, Hollier said.
These latest observations of Asian soybean rust were on maturity groups IV and V in the R4 to R6 growth stages, Hollier said. These two maturity groups are the ones most often planted by Louisiana farmers. During the R4 to R6 growth stages, the pods are formed and beginning to fill.
"This is a critical stage for yield potential," Hollier said.
"It must be kept in mind that Asian soybean rust will not be the only disease present in a field and that management practices should be broad spectrum enough to take care of other common diseases such as aerial blight, anthracnose, pod and stem blight and the Cercospora diseases," Hollier said.
In-season management practices for Asian soybean rust center on intensive scouting and, if needed, fungicide use, Hollier said. Fungicides are tools that will reduce the impact of the disease on yield.
Several fungicides are available through an emergency exemption process in which the U.S. Environmental Protection Agency (EPA) allows products close to but not fully registered to be used in a specified emergency, Hollier said.
"A list of available fungicides and specific information about the use of these is available at local LSU AgCenter offices," Hollier said.
Previous confirmations of Asian soybean rust have occurred in Louisiana in 2007, but all of those were on kudzu, Hollier said.
"Kudzu is one of nearly 100 other hosts for the fungal disease pathogen," Hollier said. "All of the previously reported sightings on kudzu were in Iberia and St. Mary parishes. Although soybeans are grown near the positive kudzu site in those parishes, no rust on soybeans has been reported from that area."
Asian soybean rust was first found in North America in November 2004. Since that time it has been found earlier and earlier in Louisiana, with the 2005 sighting in mid-October, the 2006 sighting on June 30 and the 2007 initial report on May 9.
"This pattern indicates that the fungus that causes Asian soybean rust may be overwintering in the coastal region of Louisiana on kudzu or another host that may be less affected by freezing temperatures during the winter months," Hollier said. "If it is proven that the fungus does overwinter in Louisiana, then that would mean that Asian soybean rust will be a factor in soybean production for years to come."
The LSU AgCenter provides a toll-free telephone hot line with the latest information about Asian soybean rust: 1-866-641-1847.