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Mysterious Weeds in Your Garden Might Be Your Fault Indicates Study

Timothy Boyer Ph.D.'s picture
Bird feeders a source of weed seed

Have you ever wondered why every spring a mysterious weed in your garden or yard pops up? A new study shows that it could be you or your neighbor’s fault due to common winter-time good intentions.


Contaminated Birdseed

A new study points out that there’s a very simple reason why some new weeds are popping up in homes and crop fields—commercial bird feed mixes are actually contaminated with seed species along with the desired grains used in bird feeders.

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This study published in the journal Invasive Plant Science and Management by University of Missouri researchers, under the direction of MU Extension weed scientist Kevin Bradley, have discovered that in particular the seeds from an invasive species known commonly as “pigweed” are finding their way into commercial birdseed in alarming numbers.

Dr. Bradley’s studies include the development of programs for the prevention and management of herbicide-resistant weeds; a growing problem in not just field crops, but also in public causeways, parks, neighborhoods, yards and gardens. Because birds are active carriers and depositors of seeds that travel through their digestive tract, unwanted plants can easily spread from state to state in just a short period.

So, just how much of unwanted seed can be in that bag mix you set out in your birdfeeder this past winter? In the case of pigweed seed, Dr. Bradley and his research team counted an average of 384 seeds per kilogram; however, from some sources of bird seed that number reached over six thousand seeds per kilogram sold.

In the study, 98 commercially available bird feed mixes were analyzed and what was found was that:

• The mixes contained seeds from 29 weed species.
• 96 percent of the mixes contained seeds for pigweed species of weeds.
• Seeds from kochia, common ragweed, foxtail species and wild buckwheat were also found in many of the mixes.
• One in 10 contained Palmer amaranth or waterhemp seeds that demonstrated resistance to glyphosate in a greenhouse screening.

The spread of glyphosate-resistance is especially worrisome. Glyphosate is one of the most widely used herbicides in the United States. It is applied to the leaves of plants to kill both broadleaf plants and grasses—particularly in the crop fields of corn-belt states—but can also be found in lawn and garden weed control.

"While it is difficult to estimate the precise role commercial bird feed plays, there is a distinct possibility it may be an overlooked pathway for spreading troublesome weed species into new regions," stated Eric Oseland, the lead author of the study who also added that common ragweed, velvetleaf, morning glory and other weed seeds make up an “almost endless” list of contaminating seeds that can be found in most birdseed mixes.

A Solution to the Problem?

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Currently, there is no fool-proof solution to this problem. As it turns out, just like with human health supplements, there are no regulations governing what can and cannot go into a birdseed mix. However, by following a few of the following practices, you might initiate some weed control in your garden:

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Avoid birdseed waste mixes—although a less-expensive option for feeding birds, waste seed mixes sold as birdseed should be avoided.

Choose a store that specializes in wild bird food—shop for mixes that state they are specially designed for the bird species in your area. Birds are picky eaters. By providing one type of seed in separate feeders may keep birds from picking through mixes to find the type of seed they like. Even if it does contain some weed seed, less of it may be kicked to the ground as the birds feed.

Go for seeds that are unlikely to germinate—Sunflower chips and cracked corn are good options of bird food that won’t sprout. Jays, doves, quail and sparrows prefer cracked corn; whereas, jays, woodpeckers, finches, grosbeaks and chickadees like sunflower chips. Also, some suppliers offer birdseeds that have been baked, such as Nyjer thistle—a small black seed that appeals to finches, juncos and pine siskins—that are unlikely to germinate after being heat-treated.

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If you have a favorite alternative to birdseed that you use that could be a solution to this problem, let us know what you use in the comments section below.

Timothy Boyer has a Ph.D. in Molecular and Cellular Biology from the University of Arizona. For 20+ years he has been employed as a freelance health and science writer. Today, with a background in farming and an avid home gardener, Timothy continues writing about science with a focus on the connection between plant biology and gardening for healthy living. For continual updates about plants and health, you can also follow Timothy on Twitter at TimBoyerWrites.

Image courtesy of Pixabay


Examination of commercially available bird feed for weed seed contaminants” Eric Oseland, Mandy Bish, Christine Spinka, Kevin Bradley. Invasive Plant Science and Management, 2020; 13 (1): 14 DOI: 10.1017/inp.2020.2

MU researcher finds pigweed in birdseed and pollinator mixes” by Linda Geist; University of Missouri Extension news, Wednesday, July 19, 2017