Louisiana’s mild winter, lacking temperatures that hover in the upper teens and lower twenties, could well be the reason for the earlier appearance of Asian soybean rust in south Louisiana.
LSU AgCenter plant pathologist Clayton Hollier said the Jan. 2 discovery of the disease in kudzu on Perkins Road is nothing to be alarmed about. It is just a situation that will need to be watched.
“Finding the rust is not really new following mild winters, but finding it in eight parishes mainly along the coast, and also finding it in 6-inch-high volunteer soybeans, is new,” Hollier said.
These findings tend to show that the Asian soybean rust can overwinter here.
Hollier and others on his staff have become accustomed to the rust showing up at the same location in Iberia Parish each year -- until now. “It has for several years started in kudzu along this particular ditch that we call a protected site because it is well shaded by trees.”
The disease is known to attack more than 100 host plants, with soybeans and kudzu the most susceptible.
Soybean growers are advised to be vigilant, but they shouldn’t panic. Hollier said this early development of the disease would be historic for its early start, but actually it just means that growers may have to act earlier to control the fungus.
Asian soybean rust was first found Louisiana in 2004 and is believed to have been brought by winds from Hurricane Ivan early that fall.
“We looked at the track of Ivan, and we believe it picked the spores in Columbia,” Hollier said. “Everywhere the storm went once it hit land was seen to have the disease.”
In the past, freezing temperatures have delayed the emergence of the disease to the point that the soybean crop was far enough along in development to not be affected much by it.
“The chance of the disease affecting soybeans early this year can all be changed by a few nights or days with temperatures in the lower 20s.”
The disease depends on live tissue to survive, so once the host plant is killed back by cold weather, so is the fungus.
“The reason we haven’t had an epidemic here is because it takes time to build up after a freeze has killed it back,” Hollier said. “By the time it builds back up, we’re actually late in the growing season.”
Even if the disease gets an early start this year, growers have several chemicals that are very effective.
Scientists and growers tended to be alarmed by the first sighting of the disease in 2004, when LSU AgCenter scientist Ray Schneider found the disease in a field on the Ben Hur Research Farm near the LSU campus. This was the first discovery of the disease in North America.
Asian soybean rust has been known to exist since 1902 when it was found in Japan. It was largely confined to Asia until recently -- when it spread to Africa and then on to South America around 2000.
“In some of these countries, the disease actually caused 100 percent crop failure,” Hollier said.