Invasive species--possibly NOT narrowleaf bittercress
A few years ago I sent the MSU extension service a picture of an invasive plant that the local master gardeners could not identify. The response was that it was narrowleaf bittercress (Cardamine impatiens). Today I was looking at the MISIN list of invasive species and saw a request for documentation on this plant with the UM Herbarium. When I went to look at my yard (unfortunately, the plant is more prolific than ever), I saw that what I have does not appear to have the pointed auricles at the leaf base that are described on the MISIN site and the leaves are more paired than rosettes. So, what do I have?
Oakland County Michigan
This looks like trumpet vine or trumpetcreeper (Campsis radicans). Trumpet vine is an aggressive deciduous, woody vine that develops orange trumpet-shaped flowers on mature plants and seed pods in the fall. It is often found growing on fences, up telephone poles, etc. Trumpet vine is native to Michigan, but can be a nuisance as you are experiencing. It is prolific, reproducing by seed, stems that root, and sprouts from the roots of current or past plants. Perhaps you have a mature vine nearby or one that was recently cut down. If a living vine is nearby, it will likely need to be removed to prevent further infestations.
Control options depend on your intentions for the area.
Mechanical removal is not usually effective. Personally I have been battling sprouts of this plant from a vine I removed 4 years ago...hand pulling them has yet to starve the root system and I will likely be utilizing a herbicide this fall.
Glyphosate products (such as Roundup Weed & Grass Killer, among others) are effective but require persistence. Woody vines can be cut and treated just above the ground and growing seedlings (such as those in the photo) can also be treated. Cut stump instructions are explicitly stated on the product Roundup Super Concentrate. When using products containing glyphosate there are a few important points to consider. First, as with any pesticide, remember to read and follow all labeled instructions. Second, glyphosate is a broad-spectrum herbicide, meaning it will injure or kill other plants contacted during the application, so care is needed to avoid green plant material, exposed roots, and injured bark of desired plants. Third, glyphosate is relatively safe in the environment when used as labeled. It adsorbs strongly to the soil in most cases (i.e. clay and organic matter), allowing even sensitive crops to be planted shortly after application; meaning no carry-over issues are expected. Fourth, glyphosate alone can take up to 14 days to show full activity under ideal growing conditions. Retreatment of the area may be needed depending on the degree of infestation. Glyphosate is most effective for perennial control in the fall but can be applied anytime the plants are actively growing (temperatures consistently above 50F). Finally, be sure that the product you choose has only the active ingredient glyphosate or glyphosate + pelargonic acid. Products with additional active ingredients may have other unwanted effects and may delay the planting of other plants in the coming season(s).
Another option that may be more potent is the active ingredient triclopyr. This can be found in products such as BioAdvanced Brush Killer Plus or it can be found in combination with glyphosate in Roundup Concentrate + Poison Ivy & Tough Brush Killer. Triclopyr will persist in the soil for up to several months, so it is not recommended for areas that you will be planting desirable vegetation in soon.
With either herbicide, reapplication may be required due to the aggressive nature of trumpet vine.
Thank you very much for that quick response. Is trumpet vine an actual vine? This plant is not, although it sprawls all over and gives that impression. Also, I have never seen flowers on it and certainly not orange ones. It is growing at the back of our lot, under a spruce tree, with a lot of other nuisance plants, including bindweed, ground ivy, nightshade, and grapevine. This is new arrival--it first put in an appearance four or five years a go. I think originally came in from our neighbor's lot. As far as I know, they had nothing planted there. (They are not big on gardening.) Their predecessors had raspberry bushes, but I have never seen a vine with orange flowers anywhere in the vicinity. But if it is trumpet vine, then you are right. It is not going away without a fight.
Given time and the right environmental conditions it could develop into a vine, but the shade and competition you described may be keeping it from vining much and also from flowering.
Here are a couple of photos I snapped tonight in my neighborhood of trumpet vine sprouts that get mown in the lawn and survive. The main vine on the telephone pole was killed several years ago. It has regrown and the sprouts in the lawn keep coming. The photo of the curb shows that those ones are starting to vine.
That is very discouraging to hear! Thank you. I'll keep trying to get rid of it.