The chart above shows reduction in northern willowherb growth 90 days after potting as a result of herbicide application. The entire shoot system of all NWH plants were harvested and weighed to determine shoot weight. The smaller the bars in this chart, the better the control. The bar labeled 'Control' represents containers not treated with any herbicide, and thus serves as control or comparison to herbicide treatments.
Seed from northern willowherb are disseminated by the wind, thus just a few plants can quickly infest the entire container system. Sanitation to remove existing plants from non-cropland areas, and a physical barrier around the nursery to prevent introduction of seed from outside areas will reduce populations in the nursery.
In this research, the granular herbicides Broadstar, Rout, and OH2 reduced fireweed growth greater than 50% in containers. It should also be noted that northern willowherb in this study came from natural infestations. That is, we did not overseed these containers with weed seed, they just blew in. We felt there was sufficient and uniform pressure to make this study valid. We are just now learning how to collect the seed from this plant to use in future studies, which would allow for more controlled experiments.
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