At the beginning of August, we released 100 root boring weevils to help control a population of spotted knapweed at the Anoka Nature Preserve (ANP), in the City of Anoka. Spotted knapweed is an invasive plant native to Eurasia that is spreading across Minnesota. It releases a toxin that threatens nearby plants, giving it the tools to outcompete and dominate, and thereby decreasing biodiversity.
Root boring weevils are a method of biocontrol that target knapweed without affecting surrounding native plants. As larvae, root weevils burrow into the roots of spotted knapweed and feed on them throughout winter and spring, leaving the plants dead or weakened. The weevils we released at ANP were adults who will lay their eggs at the base of the plants through early fall and hopefully begin to weaken the population of spotted knapweed within the preserve.
ANP was a promising candidate for root weevils biocontrol because the site has a large, dense population of spotted knapweed, and the weevils will not be disturbed by mowing or other land management activities. It can take several years to see the effects of the weevils, and the site will be monitored to see if they have been established. The weevils were provided by Monika Chandler from the MN Department of Agriculture, who delivered them in a sealed paper cup where they were kept refrigerated or in a portable cooler until the time of their release later in the afternoon.
Article and photos provided by Sally Herman, Seasonal Technician with ACD