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Is It a Weed?

April 9, 2015

This is not as simple of a question as it may seem. A weed is defined by Merriam-Webster as a plant that is not valued where it is growing and is usually of vigorous growth, especially one that tends to overgrow or choke out more desirable plants. In crop production a weed is any plant competing with the crop for nutrients, sunlight, water, and space. A volunteer corn plant in a soybean field is a weed. But the same volunteer corn plant in a corn field would be a crop. Another example is a dandelion. When it is found in an alfalfa hay field it is not a weed. However, when it is found in a turf lawn it is a weed. Location is a key factor when determining if a plant is a weed or not. Another key factor to consider is the plants use. We have to ask ourselves: does this plant have any usefulness to me or my goals. A lot of plants that are typically called weeds make great food for pollinators and wildlife. A major portion of our food supply comes from plants that require pollination. Providing pollinators food in the “off-season” is highly important for good yields during food production. So called weeds also can provide continuous ground cover to reduce soil loss and increase wildlife habitat. There are species and situations when a plant is definitely a weed. Species like eastern black nightshade, horse nettle, and ground cherry are all part of the nightshade family. These weeds can harbor diseases and pests that affect tomatoes and potatoes, which are also members of the nightshade family. All plants classified as invasive species are definitely weeds. A few examples of invasive species includes: Purple Loosestrife, Jimsonweed, Japanese Knotweed, Cheatgrass, and Multiflora Rose. Each state maintains of list of species designated as invasive. In Pennsylvania the plant list is maintained by the DCNR:


Purple Loosestrife Lythrum salicaria

Musk Thistle Carduus nutans

Musk Thistle Carduus nutans

Designating a plant as a weed is not a cut and dry process. Always consider the plants location and use. Most importantly, if you determine a plant is invasive use proper control methods to eliminate the problem.

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