In summer 2015, USDA-ARS and UC Davis Dept of Plant Sciences set up a water hyacinth control study with California Department of Boating & Waterways. The goal of the study was to determine the best of several different surfactants to pair with an aquatic-use formulation of glyphosate.
Aquatic weed trials are tricky compared to terrestrial trials, because the test sites are three-dimensional and they move around. In addition, water hyacinth is free-floating. In order to establish secure test plots, we built floating 1-m2 quadrats out of PVC pipe, swim noodles, and construction fencing.
On 31 July, we anchored the quadrats in open water within a sunken island in the Sacramento delta. Quadrats were anchored in four sets (replications) of five quadrats, and we placed about 20 rosettes of water hyacinth in each quadrat.
Rosettes were allowed to establish for 3 weeks, and on 21 August plots were treated with one of the following surfactant + glyphosate combinations in 100 GPA spray solution:
We evaluated plots on 24 September, ~5 weeks after treatment. We collected two 30 cm x 30 cm subsamples from each plot for biomass while measuring plant height and taking SPAD chlorophyll readings. At the time of sampling, the shoreline population of water hyacinth had grown to surround the plots (an increase of ~ 30 yards) so we had to pole the boat across the weeds.
In all parameters, the AgriDex + glyphosate treatment performed significantly better than other treatments. (We're showing only the height data.) Next season we hope to test other herbicides and other spray volumes to add to our control toolkit.
At the present time, the boat ramp we use to get to our plots has been closed down by a dense water hyacinth infestation.