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Elm seed bugs can be a major nuisance pest

The elm seed bug is relatively new to our area, with the first detections made in 2017 in Mesa, Delta and Montrose counties. (Courtesy of Utah State University)

Plenty of stories, or article ideas, come from the phrase “I made the mistake of opening Facebook … ”

Monday was no different. On one of the local pages was a photo of an inconspicuous insect and someone asking for identification and how to get rid of said terror. And it just so happened that this question (and the subsequent 200-plus comments) coincided with numerous inquiries and samples being brought into my office, all around the same insect.

The elm seed bug (Arocatus melanocephalus) is relatively new to our area, with the first detections made in 2017 in Mesa, Delta, and Montrose counties. In an impressive migration period, the insects have made their way down to Southwest Colorado, in large part because of the widespread presence of its host plant, Siberian elm.

First the positives: The insect feeds primarily on the elm seeds, which in early summer blow around like snow throughout our area. With a relatively high germination rate, we start to see elm seedlings pop up everywhere, and if they are not pulled in the first year or two, they can grow at a very rapid rate, putting feet of new growth on every year.

Now the negative: The elm seed bugs are a major nuisance pest, similar to the boxelder bug, as they enter homes and buildings when the outside temperatures rise in June and July. Unfortunately, they tend to have a preference for our cooler houses throughout summer, and if you have them, you probably won’t see them leave until September. Some adults may overwinter in the home, but come spring, they will venture outside to feed on the elm seeds. They only have generation per year.

The other negative is that control can be a challenge, and spraying them with insecticides (or homemade pest-control concoctions) doesn’t really work. You can vacuum them up and dump them into a bucket of soapy water; seal up your windows and doors to the best of your ability; or if you feel like insecticides are necessary, you can apply a perimeter barrier around windows or door entryways.

Last words of advice: Don’t squish them because they stink and the smell sticks with you for quite a while.

Darrin Parmenter is the director and horticulture agent of the La Plata County Extension Office. Reach him at darrin.parmenter@co.laplata.co.us or 382-6464. Get Growing features timely tips and suggestions for your garden and landscape.