Problem Weed of the Month: Garlic Mustard

Problem weed:

Garlic mustard - a herb introduced by pioneers, now an invasive plant.

Other names:

Alliaria petiolata, hedge garlic, sauce-alone, jack-by-the-hedge, poor man's mustard, jack-in-the-bush, garlic root, garlicwort, mustard root

Growth habit:

Annual, winter annual or biennial, most commonly found in moist woodlands, ditches and fencerows. Seeds are shed in June, and remain dormant for up to 20 months. Rosettes of green leaves grow close to the ground in their first year, remain green all winter and develop into mature flowering plants the following spring.

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Description:

First-year rosettes with kidney-shaped green leaves with scalloped edges grow close to the ground. The flower stalks grow 2 to 3-1/2 feet tall with clusters of small white flowers, with four petals in the shape of a cross. Seeds are produced in erect, slender, four-sided pods, called siliques, beginning in May. Siliques become tan and papery as they mature and contain shiny black seeds in a row. By late June, most of the leaves have faded away and garlic mustard plants can be recognized only by the dead stalks with pale brown seedpods that may remain and hold viable seed through the summer.

Spreads by:

Seeds only. Seeds can remain viable in the soil for up to 5 years. Each plant will produce between 150 and 850 seeds per plant.

Reasons for concern:

Garlic mustard is the "purple loosestrife" of woodlands and fencerows. It competes with native wildflowers that also flower in the spring, like spring beauty, wild ginger, bloodroot, Dutchman's breeches, hepatica, toothworts, and trilliums, stealing light, moisture, nutrients, soil and space. Wildlife and insects that depend on these early plants for food soon disappear. Cows that graze on this weed produce milk with a garlic flavour.

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May be confused with:

Several white-flowered native plants, including toothworts (Dentaria), sweet cicely (Osmorhiza claytonii), and early saxifrage (Saxifraga virginica).

Cultural control:

• The first step is to prevent garlic mustard. Watch for your first invader, and seek and destroy it immediately. Scout field edges now, and pull or hoe out invaders.
  
• Once garlic mustard is established, the goal is to prevent seed shed for several years until all viable seed is exhausted.
  
• Plants can be pulled out easily, especially if soil is moist, but new sprouts will grow if the plant breaks off. Remove pulled plants to prevent seed shed after the siliques are formed.
  
• Plants can be cut off to prevent further spread, but watch for sprouts below the cut.
  
• Prescribed burns can be used in large areas although other desirable vegetation may be damaged.
• Directed flamers can be very effective in small locations.
  
• Chemical control: Applications of glyphosate, 2,4-D/mecoprop/dicamba or triclopyr are effective.
• Care must be taken with either burning or spraying to avoid damaging desired plants. Wick wipers could be used to minimize damage.

More than meets the eye!

by Jan Schooley - Ginseng and Medicinal Herb Specialist/OMAFRA

Members of the country gentry in 1699 would be familiar with "alliaria", also known as "Jack-by-the-hedge" and "sauce-alone". Even in those days, garlic mustard was invasive and could be found abundantly under hedges and along banks. Leaves of garlic mustard were added to salads to impart a mild garlic flavour. But garlic mustard was more than a pungent salad herb. It was considered to possess many valuable medicinal properties and was used to clear infections and "encourage healing". It has been used internally for bronchitis, asthma and eczema and externally for minor injuries, skin problems that are slow to heal, rheumatism and gout. Another weed with a little more to it than meets the eye!

Related Links

• Publication 505, Ontario Weeds, p. 60
  
• Ontario Weed Gallery online
  
• Invasive Species: Garlic Mustard
  
• Garlic Mustard in Michigan
  

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