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Ft. Defiance garlic mustard growth could cause issues

Local botanist says increase in garlic mustard plants on forest floor could block sunshine to other plants

May 12, 2020
Amy H. Peterson - Staff Writer ( , Estherville News

They're not all bad, David Morin said. The botanist, who usually teaches English Language Learning and Success Center classes at Iowa Lakes Community College, said garlic mustard has been around a long time.

"They have found garlic mustard in the pottery of the hunter-gatherers in southern Scandinavia and northern Germany dating as far as 4000 BCE. From the 17th century in Britain, it's been used as a flavoring for salt fish or a sauce with roast lamb or salad. The invasive herb stayed in Europe until the 1860s when settlers brought it to North America. A hardy invader, it has dominated the understory of North American forests from New York to the Deep South, and west to the Rocky Mountains. Morin said garlic mustard is a biennial plant, meaning it completes its growth cycle in two years. The first year, it grows a rosette of leaves that appear in early summer when the seeds germinate, or in winter in southern climates as it photosynthesizes the sunlight while other plants are either dormant or have no foliage. The second year, the plants grow into a stalk that can be up to four feet tall. This time of year, May through June, they bloom with flowers developing seed pods. It's best to harvest or get rid of it before it goes to seed in the second year, Morin said.

There's no great way to control the spread of garlic mustard, however, Morin said. Each plant produces hundreds of seeds and when the pods ripen, they eject the seeds several feet away from the originating plant. The hardy seeds can stay in the soil for several years. In its native Europe and Asia, it's kept in check by dozens of species of insects that eat it, and butterflies and moths that lay eggs on it, leaving the leaves for their caterpillars to feast on while they're growing. In North America, the plant has no natural enemies to keep it under control. Combined with the fact that its large seed production causes it to spread quickly, it can easily replace most or all of the native plants on a forest floor.

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The garlic mustard's long tap root also has the ability to grow new plants from buds that form along its root. The roots are allopathic, meaning they ooze chemicals that can prevent other plants from growing near them, including tree seedlings. Morin said this makes an infestation disastrous for forests.

Private property owners have gotten rid of garlic mustard through herbicides. However, the problem with chemical herbicides is they don't distinguish between wanted and unwanted vegetation; they kill all plants.

The flowers and leaves taste like garlic, so one way to get rid of them is to pick and eat it. However, this is inefficient unless one feeds a lot of people a lot of garlic mustard.

The best way to get rid of it is manually: pull it up and discard it. Wet soil is looser and makes pulling easier. Try to get all the taproot or the plant will grow back, Morin said.

After that, they should be burned or buried.

Pulling and discarding can turn into a labor-intensive process in a large forest area, however. The seeds remain viable in soil for years. However, once the effort is made, other fighters of garlic mustard plants have found eventually tree seedlings and native plants gradually repopulate the areas where garlic mustard has been pulled.

Morin found garlic mustard plants along the road in Ft. Defiance, but the largest crowd is on the forest floor, down near the creek on the path leading from the state park lodge about a half mile into the woods.



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