EAST LANSING, Mich. — A big celebration is in order if you have made the decision to battle invasive species instead of letting them run rampant in your landscape. Congratulations on completing what can often be the hardest step when it comes to dealing with invasive species. To safeguard all of your painstaking work and to ensure that you stay ahead of invasives, there is something that you can do to ensure that invasive plants do not continue to impact property values and native plant communities in the new year.
As if treating invasive species such as phragmites and Japanese knotweed is not a monumental feat in itself, those who dedicate themselves to the control of these noxious plants cannot let their defenses down after a single chemical treatment. Neither can they take the season off now that winter has arrived. As described in previous news articles, including the MSU Extension articles Phragmites, invasions harm riparian property values Part 1, Part 2and Part 3, these invasive plants can seriously impact native ecosystems. Because the roots of these invasive plants may grow up to ten feet deep and spread even wider, the best way to control them is chemical treatment. Phragmites is best treated in August and September, and knotweed is most susceptible to treatment when it flowers in late August. By treating your phragmites and knotweed, you have taken the first step towards restoring your land.
Because they have such an extensive root system, established infestations generally need to be treated for several years. For example, a single chemical treatment may kill about 75 to 95 percent of phragmites. Fortunately, simple strategies can increase the effectiveness of future chemical treatment while instantly improving the quality of your land. The Oakland County Cooperative Invasive Species Management Area (CISMA) recommends a single winter mowing of the standing dead stalks of phragmites and knotweed which will accomplish the following:
- The dead standing stalks of phragmites and knotweed can be turned into straw, eliminating the fire hazard created by these plants.
- Views of the water and landscape can be restored, which have which had been blocked by these plants.
- Native seeds will be given a chance to germinate in the spring, restoring native plants and ecosystems.
- It will be easier to visually detect the few phragmites or knotweed stalks that regrow in the spring, so they can be retreated in the fall. This regrowth will also be shorter than it would if the infestation were not mowed, because the stalks will not have to grow tall to reach sunlight.
If treated infestations were not mowed, it would be very difficult to see the few stalks that regrow next year; this would make it very difficult to find and treat them. The dead stalks will also block the herbicide, requiring more herbicide to be used.
Because phragmites and knotweed often grow in wetlands, the easiest time to mow these infestations is in the winter, when the ground is frozen. Brush hogs and weed whackers with metal blades may be used. Some homeowners have suggested using snowmobiles or rowdy children to play games that will knock down the infestations.
Knotweed should only be cut in the winter, when the stalks are dead and brown. Cutting live green knotweed stalks in the summer without treating it may spread the infestation.
Fortunately, mowing may be necessary only once after the first treatment. With consistent annual treatments, regrowth will be minimal and may not need to be cut down. Few land maintenance activities can provide the instant gratification of mowing infestations of invasive plants. Many landowners enjoy the instant improvement in their views, safety and property values that can be achieved by mowing these infestations.