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Aug 02 2021

Purple Loosestrife control

This week we finished mapping the county roads for Wild Parsnip and Purple Loosestrife locations.  We noted that the Wild Parsnip has bolted (flowered and gone to seed) and is pretty much done causing problems for the year.  Next spring, we will begin treatment of the sites along the county roads where we expect it to grow.

We haven’t seen any purple loosestrife along the roads in Forest County yet, but it is making its appearance in neighboring counties.  Every year the question comes up: Will it help if I cut the flowers off the plants? Considering that these plants can drop 1-2 million seeds when they reach their maximum height of over 6’ or more, YES, please cut the flowers off if you have the access and capacity to do so. When you’re done make sure you clean off your footwear in case you picked up any of the tiny seeds.

If you have a smallish site, didn’t have a chance to try biocontrol yet, you can try the following.

  • 1-Cut off the flowers. The lower you cut the plant, the more you’ll stress it out since it’s wanting to send all its energy into seed production right now.
  • 2-Bag and dispose. Many municipalities will pick up if you label the bags “Invasive-Approved by WDNR for Landfilling.” I recently learned though that they don’t have to, so you may want to check. If you can’t trash, perhaps you could burn, depending on where you are. If you decide to try composting them, bury them deep under the other things you’re compositing so they get as hot as possible, and then watch the area carefully for sprouts.
  • 3-Small plants might be easily removed by pulling.
  • 4-Large plants can be dug out, if you’re able.
  • 5-Or if you aren’t vehemently opposed to chemicals, treat what’s left with glyphosate (Roundup).  

If the plant has reached the stage where it’s more like a woody shrub, a treatment for woody plants would possibly work better. Keep in mind that if the site is wet, you must have it done by a certified chemical applicator and have a permit. Minimally, wet is defined as so sloppy that walking on the ground with your socks on would ruin them.

Ending on a happy note. One of the reasons biocontrol is so great is that it teaches the newcomer, not native plant, to play nice with others. In a highly degraded site like this median or a wetland full of narrow-leaf cattail, purple loosestrife may be one of the few things blooming for pollinators.

Conservation Corner is a weekly article produced by the Forest County Land &Water Conservation Department. For more information contact Steve Kircher, County Conservationist-Land Information/GIS Director at 715-478-1387 or by e-mail at lcc@co.forest.wi.us.