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Friday - August 01, 2008

From: Bozeman, MT
Region: Rocky Mountain
Topic: Invasive Plants
Title: Wild mustard growing in disturbed ground in Montana
Answered by: Barbara Medford

QUESTION:

I have recently planted "plugs" of wildflowers in beds throughout my yard. Because the soil was disturbed, I now not only have some beautiful wildflowers growing, but also mustard plants growing in the wildflowers. And lots of them! Do I need to weed out the mustard plants this year? Or will they die back naturally and the wildflowers will take over next year? Will they compete with the wildflowers for moisture and light? Do I need to even worry about mustard plant invading my beautiful wildflowers? Thanks-

ANSWER:

First of all, it took us a while to discover just what plant wild mustard is. There are so many common names and synonyms for it that it was very confusing. However, we finally established that Sinapis arvensis is the common weed that is most likely infesting your garden. The first thing we want to say is YES, get rid of the mustard plants and do it quickly, because now is the time they are seeding out. They are very difficult to get rid of because they have establish a long-lived seed bank of their own. Pull them out and dispose of them so that their seeds will not spread. Apparently, they generally only show up in disturbed ground, as you pointed out, but although they are native to the Meditteranean area, they now show up all over the world, and appear in all states of the United States, including Hawaii and Alaska. They are classified as a noxious invasive in several western states. They are said to be poisonous to livestock once their seedpods are formed. Many of them harbor an eelworm that attacks other crops, therefore it is best not to grow them in a garden setting. In a word, they've got to go.

Wild mustard is considered a winter annual, which means it will bloom and seed in cool weather, but in Montana, it may very well do so in the Summer. See this website from the University of Missouri Extension on wild mustard.

The wild mustard not only will shade out and crowd out your other plants, but their seed distribution will only make the problem worse. They will not "die back naturally". They are annuals just as most of your wildflowers are, but you need to stop them before they seed. They are not altogether unattractive and if a few get by you and bloom next year, that's not a disaster. But don't let them seed.