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The P&PDL Picture of the Week
for 12 May 2003



Garlic + Mustard = A Problematic Invasive

Glenn Nice, Botany and Plant Pathology, Purdue University
Rich Dirks, Botany and Plant Pathology, Purdue University

If you are like me and enjoy a good hike in Indiana’s woods or if you are more of an urban hiker and enjoy Indianapolis’ Monon trail, you probably have seen garlic mustard (Alliaria petiolata). In fact, you may have seen it in state parks, yards, fence rows, along river banks, roadsides or ditches; just about anywhere there is a shady spot.

As the name indicates, garlic mustard is a member of the mustard family (Cruciferae). This gives it many of the characteristics that we see in other mustards, such as flowers with four petals. However, the petals are tiny and white (2 to 7 twelfths of an inch). We often falsely assume all mustards have yellow flowers. Like many other mustards, garlic mustard produces seeds in long (1 to 2 inch) two chambered pods called a silicle. Its life cycle lasts 2 years, making it a biennial. The first year is spent as a rosette of kidney-shaped leaves. When these leaves are crushed they smell like garlic, hence the other part of this plants name. In the second year of growth, stems can grow up to 4 feet tall. The second year is also when the plant produces flowers. Garlic mustard will bloom around the month of May. The second year leaves are somewhat triangular with sharp-toothed margins.

The problem with garlic mustard is that it is an invasive plant. This means that it was introduced into the ecosystem and is causing some form of damage. In the case of garlic mustard, this damage is in the form of displacing native woodland wildflowers. Garlic mustard can completely cover the floor of the forest choking out native plants. It was introduced from Europe and believed to be brought over by settlers who used it for its suspected medicinal properties.

Often garlic mustard grows in woodland or natural areas where the use of herbicides is not desired. In these areas hand pulling is often used as a control method. This can be effective with small stands, but could be quite labor intensive with large stands. A colleague of mine once suggested having a “garlic mustard pulling party” with a large stand of garlic mustard. With the right atmosphere and the right friends this could be quite fun. However, hand pulling can disturb the soil in the area and possibly damage native wildflowers growing between the garlic mustard. When hand pulling, make sure to remove the upper portion of the root. This inhibits the garlic mustard from budding. Mowing or cutting can also work. Cut plants close to the soil surface before the development of flowers in the second year. Fall burning can also be an effective management tool.

In some cases the most practical control method involves the use of a herbicide. Products containing glyphosate can be applied in the fall or early spring, when many desirable plants are dormant. Be careful with glyphosate, it can damage any growing desirable vegetation. Another option is to use herbicides with the active ingredient triclopyr in the spring. Whether you hand pull or use a herbicide, garlic mustard seed can survive in the soil 2 to 5 years so control more than likely will not be accomplished in a single year.

Dr. Kevin Gibson, a Weed Scientist in the Department of Botany and Plant Pathology at Purdue University is presently conducting research on the ecology of garlic mustard. For more information on this research visit Dr. Gibson’s faculty webpage: http://www.btny.purdue.edu/faculty/gibson/

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Garlic mustard

Close up of garlic mustard
Garlic mustard

 

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Last updated: 9 May 2003/amd
The Plant & Pest Diagnostic Laboratory at Purdue University