Japanese Knotweed

Asked July 8, 2018, 9:43 AM EDT

Could I get some detailed methods to get rid of knotweed. Everything I find is very general. I have started cutting and injecting the stems but every site I have looked at is vague about the herbicide and strengths to use so are really not useful.

Oceana County Michigan

3 Responses

I can make some detailed recommendations, but first can you please tell me a little bit about the site and the size of the infestation. Specifically, what desirable plants are in the area? Is there any standing water in the vicinity? What products do you already have?

Soil is sandy and not wet. Infestation is a pie shape roughly 30x30x30. Area has a few small maples mixed in and larger oaks, white pine and maples outside the infestation. Had Roundup Brush and Vine concentrate but ran out. I have since contacted Oceania county soil conservation dept and am working with them. They, along with Muskegon soil conservation have a grant to treat JK and will come and treat this for me so I will probably not have to deal with it myself. However, I would still like the information for future reference.

I am glad you were able to find additional help with treatment, this is a rare opportunity! Be sure to find out what they are using and pay attention to wait times for replanting desirable species if that is part of your plan.

When using the Roundup Poison Ivy and Brush Killer Concentrate you can follow the labeled directions for cut stump applications (minus the hole drilling) or treating the cut surface with undiluted product https://www.roundup.com/sites/g/files/oydgjc121/files/asset_images/products/round_up/kill_poison_ivy...

You do run the risk with any herbicide treatment in the area though of causing damage to the trees in the area, so take extra caution. Herbicides can enter trees through foliage, green/damaged bark, suckers, and exposed roots. Some herbicides are also soluble in water and can move through the soil profile to be absorbed by the roots of desirable plants.

With most perennials, the best application timing is in the late-summer to early-fall, when temperatures are still above 50F. At this time perennials are moving resources into the root system and herbicides are more actively translocated to the roots.