How rhizome size influences Phragmites australis growth and tolerance to the roseau cane scale Nipponaclerda biwakoensis

The Louisiana coastline is receding at an alarming rate due to subsidence, sea level rise, and erosion.  The major soil stabilizing plant Phragmites australis or “Roseau cane” has been dying across the birdsfoot delta where the Mississippi river flows into the Gulf of Mexico.  An invasive scale insect Nipponaclerda biwakoensis or “Roseau cane scale” was discovered under leaf sheaths of P. australis in 2016 and is now widespread across the delta.  This insect pest is believed to be contributing to the die-off of P. australis by repeatedly stressing the plant making it more susceptible to abiotic stressors.  Phragmites australis stores energy in underground rhizomes, which provide the necessary nutrients for new shoots to sprout in the spring.  We tested the hypothesis that plants grown from smaller diameter rhizomes like those in die off areas will be more susceptible to N. biwakoensis herbivory then plants grown from large diameter rhizomes like those found in healthy stands. We conducted a field experiment in Baton Rouge, Louisiana to test how the scale insect effects plant performance traits such as plant height, percent green leaves, above ground biomass, and below ground biomass.  This research provides insight to the role of rhizome size and N. biwakoensis in the die-off P. australis and the implications for successful restoration of P. australis in the Mississippi River Delta.