Scientists from the LSU AgCenter and several other agencies met for the second annual Roseau Cane Research Summit in Baton Rouge in December 2019 as they continue to investigate the decline in the health of roseau cane, or phragmites, a vital marsh grass in the lower Mississippi River Delta.
AgCenter entomologist Rodrigo Diaz is leading the group of federal and state researchers who are looking at the possible cause of the die-offs.
“We’re looking at a number of possible causes, but there’s no way to be sure until we put all the pieces together,” he said.
Diaz and the scientists began their study of the die-off in 2016, when it was first discovered.
Jim Cronin, a professor in the LSU Department of Biological Sciences, suspects multiple stressors could be affecting roseau cane health. One may be toxins in the soil.
“We are comparing soil chemicals from where it’s died off to areas where it is healthy,” Cronin said.
With the sediments and chemicals that come down the Mississippi River and are deposited into the marshes that make up the lower river delta, phytotoxic properties could be found in the soil, he said.
Cronin plans to analyze soil samples across coastal Louisiana to look for patterns in areas where die-offs are prevalent.
Diaz said research in the previous year focused on understanding the interaction of scale insects, cane variety and salinity.
“We exposed three cane varieties to different levels of scales and salinity using an open field at the LSU campus,” he said. “After six months we found that the density of scales was much higher in cane growing at high salinity levels, and this was associated with browning of the cane. This shows the complexity of the dieback because the manipulation of one stressor, such as salt, led to greater impact of the scale.”
AgCenter coastal ecologist Andy Nyman is looking at what follows roseau cane dieback. He has found that after the die-offs, there sometimes is no roseau cane to replace it — just open water. Other times, the roseau cane returns or is replaced with other wetland plants.
Nyman said another study is looking at when the die-offs started, which may have been as early as 2013, and how the die-offs may affect river navigation.
“The bulk of the dieback is occurring at the mouth of the river,” he said. “If we lose the phragmites, it will become increasingly expensive to maintain the river for oceangoing ships,” he said.
As the cane dies, more water will “escape” from the river. And as more water escapes from the channel, the river moves slower, causing it to carry less sand, which piles up and makes it harder for bigger ships to navigate, he said.
Glenn Suir, research agronomist with the U.S. Army Corps of Engineers, said his group is using remote sensing from satellites to collect data.
“We’re able to look at larger areas and over a longer time period using satellite data than what a lot of folks can do out in the field,” Suir said.
When the group began their study, they were mainly interested in roseau cane scale, an insect known to damage the plant. Results demonstrated that scale attacks only roseau cane and not crop grasses. In the second year, other scientists joined to look at other plant stressors, including soil toxins and pathogens that may be responsible.
Johnny Morgan is a writer and photographer with LSU AgCenter Communications.
(This article appears in the winter 2020 issue of Louisiana Agriculture.)
Members of the research team studying the causes of the roseau cane die-off are, left to right, Leslie Aviles, LSU AgCenter research associate; Jim Cronin, LSU professor in the Department of Biological Sciences; Nick Uzee, student worker; Rodrigo Diaz, AgCenter assistant professor in the Department of Entomology; and Madeline Gill, AgCenter research associate. Photo by Trebor Victoriano
The research team is growing the roseau cane in cattle tanks at the LSU Innovation Park, south of the LSU campus, and subjecting these plants to a number of stressors including flooding, pathogens and variations in nutrients to look for possible causes of the die-off. Photo by Rodrigo Diaz