Horsetail/Mare’s Tail Weed

Asked July 1, 2020, 2:49 PM EDT

We have a terrible problem with horsetail/mare’s tail weed in one of our flower gardens. It is EVERYWHERE. If left to grow, it carpets the entire garden. I don’t like using poisons, but I’m at my wits’ end. When I look online, there’s a treatment available, but it only seems to be available in the UK. Is there a product you would recommend? Thank you

Washtenaw County Michigan

1 Response

Hello,

This is an annual weed and difficult to control as you have noted. Unfortunately I found no gardenbed controls specific for horseweed. Here is a discussion on using non-selective herbicides, mulch, and seed prevention as ways to manage it:

Conyza canadensis, common name horseweed or marestail is an annual weed.

Horseweed spreads by seed produced in the summer. Seed can be carried on the air. Horseweed is found through out the United States. It can be controlled when small with 2,4-D in lawns. It is resistant to glyphosate. https://www.minnesotawildflowers.info/flower/canadian-horseweed

Note that the active ingredient 2,4-D can harm your garden plants, too. Please read the label and do not use a product meant for use on lawns in your garden beds.

It is a common weed in field crops: https://www.canr.msu.edu/weeds/extension/marestail-horseweed

Keep plants mowed or cut down so they don’t flower and drop more seed. Use a hoe or perhaps a weed whip. Be sure your mulch is applied 3 inches deep which helps suppress germination for next year. Keep beds mulched year around, with mulch pulled back a couple inches from the stems of your ornamentals.

You can try using a pre-emergent weed control labeled for use around established flowers and perennials, which prevents seeds from successfully germinating. Apply this in early spring and then again in the late summer to early fall when most horseweed germinates for next year. Do not apply pre-emergent chemicals to soil you will be planting ornamental seeds or seedling in. I couldn’t find homeowner information about how successful this control is, so no guarantee it will work well.

Horseweed is reported to be resistant to glyphosate in some areas. But you may try spot treating a few of your horseweed plants to see if it will work on yours— shielding all plants you want to keep from the spray, because glyphosate is non-selective and kills garden plants, perennials, and grass, too.

Always follow all label directions and precautions on any garden product.

This fall if you learn to recognize the small rosette stage and remove these, the work may be easier for you.