Ask a Master Gardener: Invasive Insect Update
My gardens are still not quite put to bed yet for the year—I’m still harvesting collard greens, kale, walking onions and a variety of herbs. They taste even more precious this time of year, knowing how little time I have left to pick something (anything!) fresh from my yard. Bugs are few and far between, too, which gives us all a little breather so that we can start fresh again next year.
Question: Are there any updates on emerald ash borer? What other invasive pests should we be aware of?
Answer:
Great question. Let’s start with the ash borer—it’s become a poster child for invasive insects. According to a recent Star Tribune article, emerald ash borer has spread to central Minnesota. This was confirmed in both Benton and Mille Lacs counties this fall.
Those counties are now included in a firewood-moving restriction; the borer has now been confirmed in 44 Minnesota counties.
What’s an ash tree lover to do? Use this interactive map to see whether borers are in your area—if you live in the southern half of the state, they likely are. If they are nearby, take stock of your ash trees. If you have healthy trees and really love them, consider getting them inoculated by a local tree care company. This must be done before they are infested, so don’t wait. (See the damage ash borers cause in the feature image above.)
If you’re feeling so-so about your ash trees, start thinking about replacement trees. The National Wildlife Federation recommends “keystone” trees for the best ability to adapt to climate change and support wildlife. Minnesota has three bioregions:
- Northern Forests (northern half of the state)
- Eastern Temperate Forests (middle and east of the state, including the Twin Cities)
- Great Plains (southwestern section of the state)
You could also use this simple guide from the Minnesota DNR if bioregions feel overwhelming.
Update on Japanese beetles
Every gardener knows about Japanese beetles. But two bits of information might be interesting to you: beetle parasite winsome flies are starting to make a difference here in the Twin Cities. If you see a Japanese beetle with a white dot or dots near its head, that is a winsome fly (see photo). Finally, the best possible revenge: Japanese beetles are edible!
I really like this article from Extension on how to manage Japanese beetles without grabbing a bottle of pesticide. Avoid those bag traps that are still sold in stores. They can end up attracting more of these metallic green menaces to your yard.
New invasive insects
Keep an eye out for two new invasive insects in Minnesota—both were confirmed by homeowners and the Minnesota Department of Agriculture’s Report a Pest service in August: elm seed bug (Arocatus melanocephalus) and Asiatic garden beetle (Maladera formosae).
The elm seed bug is more of a nuisance pest—it feeds on elm seeds and also occasionally linden and oak. It’s a bit like a boxelder bug; it might invade your home at times but shouldn’t cause widespread plant damage. Here’s a useful info sheet on elm seed bugs.
Asiatic garden beetles are definitely the more worrisome of these new bugs. They feed on over 100 hosts, including fruit, vegetables, perennials and annuals. They serve up a truly unhelpful double whammy: the grubs feed on roots and the adults feed on foliage. Their favorites? Butterfly bushes, roses, dahlias, asters and chrysanthemums. Here’s more information on Asiatic garden beetles.
Since both of these are new to Minnesota, the MN Department of Agriculture would like to better understand where these insects may be in the state. Residents can report suspected sightings to Report a Pest or call 1-888-545-6684.
But wait, there’s more!
Spotted wing drosophila are relatively new to the northland—if you grow raspberries or blackberries you may already be aware of them. They are tiny! Fine-mesh netting is one way to protect your fruits from them.
For an exhaustive list of garden insect pests, check out this list from U of MN Extension. Not all of these are invasive species! But identification is the first step toward figuring out how to manage them.
Have gardening questions? You can Ask a Master Gardener online or call the Yard & Garden Line at (612) 301-7590.
Other helpful resources:
The Master Gardener Volunteer program
Jennifer Rensenbrink is a University of Minnesota Extension Master Gardener for Hennepin County and regular contributor to Northern Gardener® magazine. She grows native plants, vegetables and fruit in her south Minneapolis yard. You can follow her gardening adventures on Instagram.