Rodrigo Diaz, LSU AgCenter entomologist Bruce Schultz/LSU AgCenter
Rodrigo Diaz, LSU AgCenter entomologist, shows LSU graduate students Rachel Harman, center, and Madeleine Chura how the scale insect infests Roseau cane. They were in the Plaquemines Parish marsh doing a survey on May 31 with the Louisiana Department of Wildlife and Fisheries and the U.S. Fish and Wildlife Service.

Field survey collects samples to study Roseau cane pest

A tiny insect, the Phragmites scale, is attacking Louisiana Roseau cane, a plant similar to bamboo with a dense network of roots that hold marsh soil together.

A team of 16 scientists and students led by the LSU AgCenter conducted a survey on May 31 to collect samples of a small insect that’s a potential threat to the fragile marsh of lower Plaquemines Parish, La.

The tiny insect, the Phragmites scale, is attacking Roseau cane, a plant similar to bamboo with a dense network of roots that hold marsh soil together.

LSU AgCenter entomologist Rodrigo Diaz said the survey is a good start for figuring out what can be done about the pest.

“We accomplished a lot,” Diaz said. “First, to coordinate logistics for future trips. Second, we established sites for long term-monitoring. And third, we collected baseline data of the conditions of Roseau at the beginning of the hurricane season.”

Other agencies participating in the survey included the Louisiana Department of Wildlife and Fisheries and the U.S. Fish and Wildlife Service.

Also on the trip was Earl Armstrong, a lifelong resident of Plaquemines Parish, who first noticed the Roseau cane appeared to be dying on hundreds of acres about 18 months ago.

He observed that some stands of Roseau cane were so thin that an airboat could easily run through them, but a healthy stand is a challenging obstacle.

In areas of thin Roseau cane growth where the cane was growing back, the scales had already started feeding on the stalks of the new plants.

Thousands of acres

The large swaths of sick Roseau cane could make it difficult to wage a campaign against the insect. “There’s no telling how many thousands and thousands of acres are affected,” Armstrong said.

Armstrong used one of his airboats to bring Diaz and graduate students Rachel Harman and Madeleine Chura into the marsh to collect samples at 10 locations between Venice and West Bay within 4 miles of the Mississippi River terminus at the Gulf of Mexico.

Armstrong knows the marsh well, having grown up in Pilottown, a small village on the lower stretch of the Mississippi River that’s home to river pilots and fishermen.

Armstrong’s father and grandfather had the job of maintaining the navigational lights along the lower Mississippi River. His grandfather settled in lower Plaquemines Parish in the 1800s.

Armstrong has made a living from a variety of work in the marsh, including gill netting, alligator trapping, trawling for shrimp, hunting alligators, nutria and muskrat, and operating an offshore workboat.

Hurricane Katrina demonstrated the coast’s vulnerability with a 12-foot tidal surge that changed the area landscape and economy forever, Armstrong said. He lost 1,500 head of cattle, including 91 registered bulls, in the marsh killed by Katrina. Since the storm, he has rebuilt his herd to 500 head.

Some Roseau cane has regrown since Armstrong first noticed it dying, but the results are not encouraging.

Scales on young plants

At one location, cane that had died from the scale was starting to grow new shoots, but scales could be found on the young plants.

“This is new growth, and it’s going to be dead in January,” Armstrong said. “You don’t see a lot of healthy growth.”

Armstrong has discovered a smaller type of cane where no scale has been found so far, and Diaz said that species will be explored to see if it could be propagated to grow as a replacement for Roseau cane.

At one of the last stops of the day, a stand of Roseau had no scales and still had lush growth, so much so that the dense growth had to be broken down to clear a path for the airboat. “This is the way it’s supposed to look,” Armstrong said.

Diaz and LSU ecologist Jim Cronin are going to look at the healthy cane from that location to see if it has some resistance characteristics that scales don’t like.

“The scales we collected will be used for several experiments, including the laboratory evaluation of insecticides and Roseau variety resistance,” Diaz said.

Also in the lab, Diaz will study tiny parasitic wasps that prey on the scales to see if that insect could be recruited as an effective control agent of the scales.

Scales have been found on Roseau cane along the roadside north of Venice, he said. The sampling team will do a series of scouting trips along the coast to find out the extent of the scale’s range in Louisiana.

Female scales

Female scales cling to the stem, Diaz said. Mature females are oval, pale yellow to brown in color, and measure slightly less than a half inch long.

The insects originate from China and Japan, but how they got to Louisiana is uncertain.

How they will be controlled is also uncertain. Chemical control is being considered; however, most insecticides could harm aquatic life in the marsh.

Scales are controlled with fire in China, but that method would be difficult to use in Plaquemines Parish, which is crisscrossed by pipelines and other oil and gas infrastructure.

Diaz has applied for federal and state funds work on finding a solution to the problem.

Research is essential to addressing the insect’s threat to the marsh, said Rogers Leonard, LSU AgCenter associate vice president for plants, soils and water resources.

“We understand the urgency for finding a solution to this problem,” Leonard said. “Before we prematurely put forth a management strategy, we need to develop science-based recommendations to find the most effective and sustainable way to control this invasive insect.”

Dynamic environment

“The Louisiana coastal system is a dynamic environment that is very sensitive to change, and we don't want to cause long-term damage with our actions,” he said.

Armstrong is worried that if nothing is done, the scale could cause the marsh ecosystem to collapse.

“I hate to even think about it,” he said. “It’s going to be so bad.”

Rodrigo Diaz can be reached at 225-578-1835 or [email protected].

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