(01/24/22) BATON ROUGE, La. — Five and a half years after the initial discovery of large dead patches of roseau cane on Louisiana’s coast, LSU AgCenter scientists and those from partner agencies have learned a lot about what is causing the marsh grass — which plays an important role in preventing land loss — to die.

They have identified an insect, called roseau cane scale, that is infesting the cane and are working to find control strategies. They also are exploring other factors that could be stressing the cane, such as salinity and sediment composition.

But many questions remain about the roseau cane dieoffs and their effects on Louisiana’s fragile coastal ecosystem. Those questions have sparked a number of research projects, which were discussed at a summit held Jan. 14 in Baton Rouge.

“Our coast provides and supports a considerable amount of economic activity, and it’s very critical that we maintain those ecosystems,” LSU AgCenter Associate Vice President Michael Salassi told the group.

Coastal Louisiana supports the energy industry and fisheries, and its wetlands are home to great biodiversity and unique cultures.

Reports of dead stands of roseau cane near the mouth of the Mississippi River started coming in August 2016. Losing large swaths of marsh grass is a concern, as the roots of those plants help hold soil in place and buffer the threat of coastal erosion.

Scientists have focused much of their effort on the scale insect they found covering samples of dead roseau cane. Native to Asia, the scale can quickly colonize an area.

The scale populations seem to be here to stay. “They are coming back every year,” said AgCenter entomologist Rodrigo Diaz.

Some good news from the scientists’ studies: “This insect is a specialist,” Diaz said. That means it can only live on roseau cane and is not a threat to other plants, such as rice, sugarcane and other agricultural crops that are economically valuable in Louisiana.

There also is cause for optimism in that at least three parasitoids in Louisiana attack roseau cane scale. Diaz said these insects show potential for biological control of the scale.

The insect, however, is likely just one of a constellation of problems affecting roseau cane.

“When stressing the cane with higher salinity levels, you notice that the scale infestations increase,” Diaz said. “We’re definitely dealing with a multi-stressor system.”

In working to develop management recommendations for this issue, it’s important to understand the complexity of the Louisiana coast — particularly in the birdsfoot delta at the mouth of the Mississippi River, where cane dieoffs have been most prevalent.

What plants can be supported in the marsh heavily depends on elevation and sediment type, which are dictated by the river’s ever-changing behavior, said Alex Kolker, associate professor with the Louisiana Universities Marine Consortium, who gave the keynote address at the summit.

There are many different types of soil in the delta, he said, from sandier areas that tend to be high and dry to clay soils and organic matter that hold a lot of water.

Management plans have to account for all of these factors and geographic variations, Diaz said, noting that sources of abiotic stress such as soil composition are a key influence on plant performance.

“We’re not going to have a single management plan that is going to work in terms of restoration,” he said. Rather, scientists are working to develop recommendations aimed at a range of problems.

The variety of issues involved in the roseau cane effort also presents exciting opportunities for scientists and students conducting research.

“Below ground, it’s a fascinating story,” Diaz said.

More information is available at www.lsuagcenter.com/roseaucane.

Open water visible through thinning stand of roseau cane. Photo by Rodrigo Diaz/LSU AgCenter

Roseau cane scale. Photo by Rodrigo Diaz/LSU AgCenter