I have been a Minnesota Extension Master Gardener for over 23 years and I am happy to say that I am still learning new things about horticulture every day.

One of the big perks of being a Master Gardener is easy access to the experts at the University of Minnesota and almost immediate answers to any garden questions that may come up.

For instance, last fall a huge lilac in my backyard lost all its foliage long before it normally does. In the spring, very little new growth and that started to turn brown and die after only a few months. Apparently, this was also happening to lilacs in the Twin Cities and many homeowners were sending specimens to the U of MN Plant Disease Clinic -- pdc.umn.edu -- for diagnosis.

The clinic experts shared their findings with the Master Gardeners and it turns out it is a fungal disease called pseudocercospoa leaf spot and the best treatment is keeping all the dead leaves cleaned up under the shrub and also strategic pruning.

In the process of researching lilacs and the pseudocercospora leaf spot, I made a startling discovery. I had always assumed that lilacs were native to North America and I was surprised to find out they are actually native to Europe and Asia. Who knew?

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There is nothing wrong with lilacs — except for pseudocercospoa leaf spot — but that leads me to the topic of this article. How much do we really know about our plants? Here is a list of non-native plants very commonly grown here that have become invasive and are considered a noxious weed by the State of Minnesota. I’ve also included some plants that are native, have attributes, but can become aggressive and out-compete other native species.

Invasive non-native plants

Winged Burning Bush (Euonymus alatus)

Burning Bush is a frequently planted ornamental shrub grown for the vivid red autumn color. Easy to identify it has a unique winged corky stem. Like Buckthorn, Burning Bush becomes invasive in the woodlands choking out native understory. It is in a three-year production phase-out and will be moved to the MN Restricted Noxious Weed list beginning January 1, 2023. For those who do have this shrub it would be advisable to remove them before they officially go on the Restricted List in 2 -1/2 years.

Japanese Barberry Cultivars (Berberis thunbergii)

Japanese Barberry is another commonly grown ornamental shrub chosen for foliage color and because deer do not browse it. When Japanese Barberry escapes into the woodlands it forms dense thorny thickets that are impenetrable by wildlife. Many cultivars were put on the MN Restricted Noxious Weed list in 2015 because they produce copious amounts of seeds that are planted by birds. For a list of the restricted cultivars, see the link below. If you have one of the cultivars growing in your yard it is advised to remove and replace it with a different species of shrub.

Common Barberry (Berberis vulgaris)

The same as Japanese Barberry cultivars above, except all Common Barberry is on the MN Prohibited Noxious Weeds Control List.

Queen Anne’s Lace (Daucus carota)

This one really pains me. I have always enjoyed Queen Anne’s Lace and the unique way it makes a basket of seeds after blooming. I will even admit that I planted it in my own gardens at one time. Well, the bad news is it is on the MN Restricted Noxious Weeds list. When you look at the photo, it’s pretty evident why.

Aggressive native plants

Daisy Fleabane (Erigeron strigosus)

'You see this plant growing everywhere. It has small white daisy-like flowers that can sometimes have a pink or blueish tinge to them. I am often asked to identify this plant in newly established prairie plantings. Homeowners want to know: Was it planted with the oth

Daisy Fleabane is messy and can become a nuisance in prairie plantings. Terry Yockey / Master Gardener
Daisy Fleabane is messy and can become a nuisance in prairie plantings. Terry Yockey / Master Gardener
er prairie plants? Is it good or bad? Good questions, and my answers would be no, and it is both good and bad.

Daisy Fleabane is a native Minnesota plant and good for pollinators, but if left in a prairie planting will soon crowd out the more attractive prairie plants.

White Snakeroot (Ageratina altissima)

This native plant has a notorious history. When the pioneers began to move west, new settlements were stricken by a mysterious tremor disease that was named the “Milk Sick.” The tremor sickness struck in late summer and almost everyone who got the illness died. One of the more notable victims of the disease was Abe Lincoln's mother, Nancy Hanks Lincoln.

A white snakeroot plant grows through a landscape hydrangea. Terry Yockey / Master Gardener
A white snakeroot plant grows through a landscape hydrangea. Terry Yockey / Master Gardener
In the early 1900s the cause was found to be the toxin Tremetol and the culprit was the White Snakeroot that cattle had been grazing on in the woodlands.

History aside, White Snakeroot grows all around our area, does well in the shade and has a dense root system that chokes out almost all other vegetation including the dreaded wild parsnip.

Canada Goldenrod (Solidago canadensis)

Goldenrod is not what causes allergies in late summer—it is the ragweed blooming at the same time. Goldenrod is an important part of the migration of the monarchs giving them needed fuel as they make their way to Mexico.

Canada Goldenrod will establish itself and populate a large wild grassy area. In a smaller landscape, however, it is a bully and will crowd out almost any other plant. A better choice for the home landscape would be a more restrained species like the very attractive Stiff Goldenrod (Solidago rigida).

Ask a Master Gardener

If you have questions or need help identifying a plant in your landscape, contact the Goodhue County Master Gardeners at goodhuemgs@gmail.com. Interested in becoming a Minnesota Master Gardener? We are taking applications until Oct. 1, find information and an online application at z.umn.edu/mgapplication.

References:

hortnews.extension.iastate.edu/lilac-pseudocercospora-leaf-spot

www.mda.state.mn.us/plants-insects/minnesota-noxious-weed-list

www.dot.state.mn.us/roadsides/vegetation/pdf/noxiousweeds.pdf