Testing the efficacy of an organic acid and sucrose-based organic herbicide on invasive Phragmites australis

Danielle S. Snow, U.S. Geological Survey, Great Lakes Science Center, Ann Arbor, MI, Kurt Kowalski, Great Lakes Science Center, U.S. Geological Survey, Ann Arbor, MI, Wes Bickford, Ecology and Evolutionary Biology, University of Michigan, Ann Arbor, MI and James White, Plant Biology, Rutgers University, New Brunswick, NJ

Background/Question/Methods
Non-native Phragmites australis is an aggressive invader of wetland ecosystems across North America. Conventional management approaches for controlling the spread of invasive P. australis are often labor intensive or involve the use of non-specific chemical herbicides. Recent efforts have demonstrated that rhizosphere and endophytic microbiota can be manipulated to affect nutrient acquisition and plant growth. For instance, previous work has demonstrated that the application of organic acids to soils negatively affects the health of P. australis, presumably by disrupting nutritive symbiosis. Additionally, carbon amendments to soils can immobilize plant-available nitrogen. We aimed to explore whether P. australis can be controlled through manipulations of soil microbiome via organic acid and sucrose amendments. Over two field seasons, mesocosms of P. australis were treated with combinations of (1) calcium butyrate and calcium propionate organic acids, (2) 30% and 50% sucrose, and (3) stem cutting to test increased plant stress in combination with microbiome manipulation. We applied weekly or monthly doses of treatments as a foliar spray and/or poured organic acid and sucrose treatments directly onto the soil surface. We harvested plants at the end of the growing season and collected data to characterize plant health. Bulk and rhizosphere soils were collected for microbial DNA extraction and metagenomic analysis.
Results/Conclusions
Treatments resulted in significantly reduced P. australis growth compared to controls (p < 0.001). Treatments containing sucrose had the largest affect on P. australis, with plants showing signs of stress and die back of aboveground tissue within days of treatments. Organic acids alone had minor impacts on overall plant health. Plant height, aboveground and belowground biomass, the number of primary roots, and the number of tillers were reduced in all plants subjected to treatments. Aboveground tissue nutrient concentrations of treated plants were significantly decreased for potassium, sulfur, and zinc, and increased for iron, copper, and aluminum. These results suggest that applications of sucrose and organic acids may be disrupting nutritive symbioses, thus leading to declines in biomass production. We propose that sucrose in combination with organic acids may therefore have the potential to be used as an organic herbicide for the management of invasive P. australis.