At a previous residence, Japanese knotweed was the bane of my backyard gardening endeavors. Masses of these invasive plants can easily stifle native or non-invasive plants. The roots grow deep and even small pieces left in the ground can re-grow new plants. I used frequent hand-pulling and digging in an attempt to keep it in check, and I knew that if I stopped it would just grow back. For more information on this invasive weed, refer to this excellent fact sheet.
I have read that you can cook and eat it, but I haven’t tried. And no matter how delicious it might be, it would still be horribly invasive. While bees will visit the flowers late in the summer, there are better ways to feed the bees.
You may have heard that Cornell researchers led by Dr. Bernd Blossey released the Knotweed Psyllid (Aphalara itadori) in June 2020 in Tioga and Broome counties as a potential biocontrol agent for this invasive weed. This release came only after thorough testing and permission from the U.S. Department of Agriculture, since this insect is native to Japan. You can learn more about the process of using classical biocontrol to manage weeds here. Be assured, many precautions are taken before non-native species are intentionally released in the U.S.
Unfortunately, attempts to establish this insect in both the United Kingdom and Canada have not been successful. Preliminary results from the NY releases suggest that this psyllid will not be the biocontrol solution we need for Japanese knotweed. Most of the insects that were released do not seem to have survived and even when the insects were protected in cages put around the knotweed plants, they didn’t reduce the growth of the plants.
It seems that if we are going to solve this weed problem with biocontrol, we will need to find other insects from the native range of Japanese knotweed. Assessing these insects prior to release in the U.S. will be a lengthy process, so in the meantime keep using other IPM tools for this invasive weed.
If you’d like to learn more about this project, the New York Invasive Species Research Institute is hosting a webinar on September 30, 2020 at 11:00 AM.