Invasive knotweed control videos

Also known as "hollow stem injection" this method uses a specialized tool (injector gun) to deliver a small dose of concentrated herbicide (41% glyphosate) directly inside the hollow knotweed stem. The plant absorbs the chemical and it moves throughout its system, reaching the roots to the leaves. It is very effective and significantly decreases the potential for off target impacts but is time and resource intensive. It is most effective on larger stems and is a great option for chemical control at sensitive sites.  

There are many considerations when it comes to knotweed injection, including the following: 

• Physically demanding/access considerations: this method requires the applicator to be near or at ground level in the brush for an extended period (long enough to inject each individual stem of the infestation). If this does not sound doable, consider asking for support through friends/family, or hiring a contractor (email us for a list). Other methods like foliar spray may be easier to try depending on your site. 
  
• Site location: do not use herbicides near water unless you are licensed applicator with an aquatic endorsement and have permission to apply from the state department of ecology. Read your product label for more information.
• Infest size: this method requires you to inject each individual stem and thus is best for sites where the knotweed is relatively sparse (<2500 stems per acre) and smaller than 1 acre in size. If your infest is larger/denser, consider foliar applications for its first treatment (can plan to inject in future seasons when appropriate). 
• Timing: if your knotweed is too small (stems < ½ inch wide) or too woody (later season, needle won’t push through), consider other methods or waiting to borrow in the appropriate season July through October. 
• Municipality/local regulations: King County regulations allow residents to control listed noxious weeds on properties they manage in accordance to the herbicide label. For those who reside in any city’s boundaries, the city’s municipal regulations take precedence. Check with your local government to check for any permitting needs or other regulations to be aware of around herbicide application on listed noxious weeds. 

In some circumstances, another control method may be more appropriate – consult our Best Management Practices Guide or contact us for recommendations.

• Be sure to secure your herbicide ahead of time! Products that work for injection are getting harder to find, play it safe and get yours before picking up your injector. 
• Read the label of the herbicide you will be using! Prepare yourself with the appropriate Personal Protection Equipment (i.e. gloves, eye protection, long sleeves) and be aware of any environmental/physical constraints. 
• Know your boundaries! King County residents can find their parcel boundaries here: King County Parcel Viewer. Non-certified applicators may apply general use herbicides on their own properties. Treatments performed on land not owned by the applicator are considered commercial and require certification – even if no compensation is provided for the treatment.  
• Have the knotweed injector video link nearby for easy reference on injection day! Familiarize yourself with the process before using the tool. 

You should not dig up the remaining knotweed. When given the time to work into the system, the herbicide should travel through the root system of the plants – leaving dead roots that can naturally compost back into the soil. If digging is necessary, wait at least 1 month if possible following treatment. If it is unavoidable, be prepared for concentrated regrowth at the digging site next season (new plants will grow from broken/living root fragments). 

Wait to plant into the area at least 1 month following treatment, with the understanding that knotweed takes usually 2-5 treatments/seasons to be eradicated. While there is less every year, anticipate herbicide treatment in that area for the first couple years following initial treatment.