Phalaris arundinacea, also known as reed canary grass (RCG), is a non-native invasive grass that thrives in floodplains. RCG plants displace native flora which reduces diversity in otherwise species rich wetlands. This is a widespread problem throughout many parts of the USA. RCG can grow by its seeds or its rhizomes. Its seeds are capable of surviving long periods in soil. RCG can potentially be controlled by multi-year treatments in early spring and early fall with broad spectrum or grass specific herbicides. The goal of this study was to optimize methods to control RCG, in order to increase species diversity.
One objective was to examine effects of broad spectrum herbicide AquaNeat® (glyphosate), and grass specific Fusilade II® (fluazifop-p-butyl) applied in either spring or fall, or both spring and fall at two field sites in order to ascertain which combination(s) of treatment can potentially control RCG. Both field sites were in zones affected by floods and contained at least 95% cover of RCG. A second objective asked whether pretreatment with a plant growth hormone called X-CyteTM (kinetin), shown to release buds from dormancy to enhance impact of herbicides, would enhance any of the affects revealed by the first seasonal and herbicide based experiments.
Based on biomass measurements, single herbicide application in either spring or fall was less effective than treatment in the spring followed by treatment in the fall. Kinetin in the field appeared to have no significant effect on the efficacy of either herbicide type, but this result may be due to the timing of application. Kinetin applied at a lower height in the greenhouse successfully released above ground buds from dormancy and appeared to produce a full kill. However, further observation revealed that rhizomes were not killed. Thus, field results combined with greenhouse results suggest kinetin is of little value in augmenting kill of RCG.
Overall, glyphosate was more successful than fluazifop-p-butyl in reducing RCG biomass and percent cover. This was especially noticeable on a flat site with an initial monoculture of RCG. Treatment of glyphosate in spring and fall did not completely harm desirable plants; a stand of greenheaded coneflowers grew in a treated area where RCG was once a monoculture, probably from below ground dormant material. Spring treatment killed RCG top growth, but it was unclear whether underground rhizomes were killed. RCG sprayed just prior to flowering in summer failed to produce seed. In greenhouse experiments (likely simulating spring conditions), fluazifop-p-butyl treated plants suffered top kill, but all apparently dead rhizomes held at less than -0°C (simulating vernalization) grew new shoots after return to 23°C. This shows that early successful control may be short lived, which would require repeated treatment in successive years.