Louisiana’s coastal marsh has been under siege by erosion and subsidence. Now comes another threat: the Roseau scale insect, an invasive species from Asia. It is suspected of playing a major role in the die-off of Roseau cane in the southeast Louisiana marsh.
The insect preys on the Roseau cane, the main vegetation in the vast Plaquemines Parish marsh. The plant is the front line of defense against coastal erosion with an extensive root system that holds the fragile marsh soil.
Meanwhile, the scale insect has claimed large swaths of the cane. The scale has been found in areas where the cane has regrown after a die-off from scale infestation.
Rodrigo Diaz, LSU AgCenter entomologist, said it’s possible the insect alone is not responsible for the Roseau cane die-off. He said it’s likely that the Roseau has been subject to several stresses, such as excessive saltwater, before the scale insect bores a hole into the plant to feed.
The LSU AgCenter, in conjunction with several state and federal agencies, is researching ways of controlling the insect.
Losing the Roseau cane would be disastrous for Plaquemines Parish, which has been imperiled by coastal land loss for decades.
The banks of the Mississippi River in Plaquemines Parish are held in place by Roseau cane. The banks maintain the river channel, forcing the swift water to carry sediment through the delta and out to the Gulf of Mexico.
Without the river banks to restrict the Mississippi’s flow, the water would be dispersed and the current would slow to a sluggish speed. Sediment would fall out of the water before reaching the Gulf, resulting in siltation in the channel that would threaten the Mississippi’s viability for large oceangoing ships.
Also, the loss of Roseau cane would mean valuable wildlife habitat would be threatened, since the marsh is the wintering home for migratory and resident waterfowl.
James Harris, manager of the 48,000-acre Delta National Wildlife Refuge, said Roseau cane is the key to the delta’s survival. “As the Roseau goes, so goes the refuge.”
Bruce Schultz is an assistant specialist with LSU AgCenter Communications.
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. Photo by Bruce Schultz
The LSU AgCenter and the LSU College of Agriculture