Role of rhizome quality on the tolerance of Phragmites australis to roseau cane scale herbivory

Louisiana is losing land 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 Bird’s Foot Delta where the Mississippi river flows into the Gulf of Mexico. An invasive scale insect pest 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. Repeated years of stress from the scale weakens 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. Plants growing in die-off areas tend have smaller diameter and shorter stems than healthy stands. We conducted a field experiment in Baton Rouge, Louisiana to test how the scale insect effects height, percent green leaves, above ground biomass, and below ground biomass of plants grown from different size rhizomes. We also surveyed transects into die-off and healthy sites to document natural plant traits and infestation levels of P. australis with the scale insect. This research provides insight to the role of N. biwakoensis in the complicated story of P. australis die-off. The knowledge gained from this experiment and field study has helped to identify die-off sites and focus restoration efforts of P. australis in the Mississippi river delta.