Scale insect attacking coastal vegetation raises concerns

Bruce Schultz / LSU AgCenter
LSU AgCenter coastal ecologist Andy Nyman shows reporters how the roots of Roseau cane are more extensive than another aquatic plant known as bull tongue.

Finding a solution to controlling an insect that threatens the key vegetation in coastal Louisiana will require extensive research by the LSU AgCenter working with several other state agencies that met on June 14 to give an update on the problem.

The potential threat, and the LSU AgCenter plan for the research to devise a solution, were outlined for state and national media at the meeting.

The insect, Phragmites scale, is attacking Roseau cane, a plant that grows profusely along the coast. It is considered vital to the fragile marsh’s longevity because the plant’s root system binds the delicate soil. Large stands of the cane have been decimated by the pest, starting in the Mississippi River delta in Plaquemines Parish, and it has been found in other areas.

This is the next new threat to Louisiana’s coast,” said Randy Myers, assistant secretary of the Louisiana Department of Wildlife and Fisheries. “This is a significant problem.”

Finding an answer to the problem could require two years of work, said LSU AgCenter entomologist Rodrigo Diaz. “We’re fully aware of the urgency.”

Roseau cane is important to the delta’s survival, said James Harris, manager of the 48,000-acre Delta National Wildlife Refuge. “As the Roseau goes, so goes the refuge.”

Louisiana Coastal Protection and Restoration Authority board chairman Johnny Bradberry said an interagency meeting will be held in August. “This is a very dynamic situation, and the state is committed to addressing this problem as quickly as possible,” he said.

It’s unknown how the scale insect arrived in Louisiana, Diaz said. It has been intercepted in previous years at ports in Hawaii and California.

The scale could be spread by birds, floating pieces of Roseau cane or boats, he said. It’s important for boaters to clean their vessels after an outing to prevent spreading the insect, especially because it is unknown if this scale could infest crops.

Similar scale insects feed on sugarcane and grain sorghum, and the AgCenter will be conducting research to determine if this scale could become a pest of those crops in addition to rice and corn, Diaz said.

Myers credited Plaquemines Parish resident Earl Armstrong with reporting the cane die-off about 18 months ago. “Then a year later, we’ve seen this problem expand exponentially,” he said.

More adult scales were found earlier than expected in February, but the mild winter may have allowed the insect to flourish in the colder months, Diaz said.

The AgCenter plan calls for public education on the problem with a website detailing where the scale has been found, he said. Individuals could help by reporting scale locations they find.

Under the plan, sampling will be conducted every two months in four areas of the delta with remote sensing and other high-technology procedures, Diaz said. The rest of the Louisiana coast will be surveyed to find out the extent of the scale’s range.

Diaz will study different control methods, including insecticide applications, first in the greenhouse and later in field trials. China uses fire to control the pest, but the vast network of oil and gas facilities in coastal Louisiana hinders that approach.

Parasitic wasps are natural enemies of the scale, but it’s uncertain how the wasps could be recruited to increase their effectiveness, he said. That also will be studied under the plan.

State Rep. Chris Leopold, of Belle Chasse, said the issue transcends Louisiana because of the importance of maintaining the integrity of the Mississippi River outlets for international shipping. “This is a national issue,” he said.

Todd Baker, director of the Department of Wildlife and Fisheries Coastal and Nongame Resources Division, said losing the cane could result in a devastating cascade of events for the marsh. “If we lose this cane, very quickly you’re going to have a lot of loose soil that will erode quickly,” he said.

Baker estimated that 80 percent of the vegetation in the Mississippi River delta is Roseau cane. The channel banks that line the outlets of the river into the Gulf of Mexico are held in place by Roseau cane, he said.

Without the banks, Baker said, the silt-laden water will no longer be funneled into delineated channels, causing the Mississippi’s flow to slow down and allow sediment to build up quickly in the waterways used by ocean-going vessels.

Losing the marsh would also expose a vulnerable oil and gas infrastructure along the coast to the Gulf of Mexico, he said.

Currently, the predominant plant naturally replacing Roseau cane is the elephant ear, Baker said. But it lacks the extensive root system of cane.

Roseau cane damaged by the scale insect is attempting to make a comeback with regrowth. “The bad news is the scales are already attacking the new growth,” Baker said.

Maintaining the cane is important for all of Louisiana’s coast, Bradberry said. “This issue is critical to us,” he said. “We need it to continue to restore the coast. It’s really an issue that’s critical to all of us along the coast.”

But money must be secured to get the plan underway to save the Roseau cane, Bradberry said. “We’re talking about one of the most important things we’ve got down here,” he said.

Rogers Leonard, LSU AgCenter associate vice president for plants, soils and water resources, said the AgCenter is poised to tackle the required research.

Diaz has identified a third parasitic wasp of the scale, Leonard said. Identification of a new pest sometimes takes years, and that has been done through Diaz’s work and contacts in the scientific community.

So we are already beginning to make progress and that is in just a few weeks,” he said.

The AgCenter will be working with several other state and federal agencies to come up with a solution that is sustainable, environmentally friendly and effective, Leonard said.

LSU ecologist Jim Cronin said Roseau cane is found on all continents except Antarctica. “It probably is the most widespread plant on the planet,” he said.  “It’s got the widest distribution of any plant we know of.”

The root system makes up 60 percent of a cane plant’s biomass, Cronin said.

The plant is grown in China to help filter pollutants from water, and it is grown in Europe for roofing material and wildlife habitat, he said.

He said the cane’s root system is the best at holding soil effectively. “When we’re talking about recovering our coastal marsh habitat, Roseau is about our only option.”

The European cane began to die in the 1970s. “It took a long time in Europe just to get a handle on this,” Cronin said. The European die-off was blamed on changes to water control and other manmade environmental changes.

Roseau cane was brought to the U.S. in the mid-1800s from Europe, Cronin said. In other parts of the U.S., such as the Chesapeake Bay, it is a nuisance that has overtaken wildlife habitat.

Using fire and herbicides in the Chesapeake Bay has not been successful, he said.

The scale seems to prefer only some varieties of Roseau cane, and that variety resistance may offer a solution.

A tour of the marsh after the June 14 meeting revealed areas where the Roseau cane has been under attack, resulting in areas of open water. In some places, the cane has regrown.

It will keep trying to regrow until whatever is killing it stops coming back,” said AgCenter coastal ecologist Andy Nyman.

He pulled a few samples of cane in one area and examined them for scale. “There’s hope because there’s not many scales,” he said at one stop.

Nyman also has found some areas where cane has died, but no scales were found, suggesting the possibility that the cane is affected by a combination of unknown factors that make it vulnerable to scale insects.

Diaz is recruiting other AgCenter and LSU faculty to participate in the research to explore what those unknown factors might be.