Uprooting invasive knapweed

By Kary Askew Garcia, MNA Intern

A moth rests atop a knapweed flower. Photo courtesy of MNA archives.

A moth rests atop a knapweed flower. Photo courtesy of MNA archives

MNA is hosting several stewardship events this summer to remove the invasive knapweed plant from various sanctuaries.

The invasion of knapweed poses a danger to native plant life and must be uprooted. The knapweed’s origins are traced back to southeastern Europe. The plant begins to grow as a rosette of leaves in its first year of life and then later on grows a flower stalk ranging from six to 36 inches in height. The flower is usually pink or purple in color with a spotted head underneath, as knapweed is also referred to as “spotted knapweed.”

Knapweed can be found in well-drained soils, dry prairies and dunes. Knapweed is especially harmful to oak barrens, which are endangered worldwide.

The weed’s invasion has caused a decline in native plant species, which is threatening to the ecosystem. It can also alter water quality by causing an increase in soil runoff and erosion.

Spotted knapweed growing on dry terrain. MNA archives.

Spotted knapweed growing on dry terrain. Photo courtesy of MNA archives

Two common ways of eliminating knapweed are simply pulling the plants or mowing them down. There are also herbicides and chemicals that can also be used for removal but have several regulations and must be used carefully as to not upset any other plant or wildlife.

Two different insects have also been introduced to inhibit the knapweed from spreading seeds: flower weevils and seedhead flies. These insects introduced to the knapweed are a form of biological control of the invasive species.

Of these methods, MNA has most commonly uprooted the weed. Uprooting sounds much easier than it is, involving tools to help pull as many of the knapweed’s roots out of the soil as possible. If left behind, the roots could help the weed grow again and damage native plant life.

The knapweed has a tendency to knock out all other vegetation surrounding it, making many ecosystems bare if it isn’t removed.

MNA has also used prescribed burns and herbicide to remove larger amounts of knapweed in sanctuaries. Simply pulling knapweed when it is extremely abundant wouldn’t prove effective; burns and chemicals have helped to reduce the occurrence of the plant.

For more information on spotted knapweed, see Michigan State University’s Agriculture and Natural Resources website here.

Volunteers and stewards help pick knapweed at an MNA nature sanctuary. Photo courtesy of MNA archives

Volunteers and stewards help pick knapweed at an MNA nature sanctuary. Photo courtesy of MNA archives

MNA is calling for volunteers to help pull spotted knapweed from different sanctuaries. The next pull will be hosted at the Calla Burr Nature Sanctuary in Oakland County on July 10 from 9 a.m. to 1 p.m.

More upcoming knapweed removal events:

  •  July 22: Volunteer Day: Lefglen Nature Sanctuary in Jackson County. 9 a.m. – 1 p.m.
  • July 25: Spotted Knapweed Pull at Calla Burr in Oakland County. Begins 9 a.m.
  • July 26: Spotted Knapweed Pull at Keweenaw Shores II Plant Preserve in Keweenaw County with Nancy Leonard. Begins 11 a.m.
  • August 9: Hike & Volunteer day: Redwyn’s Dunes in Keweenaw County. Begins 11 a.m.

Please contact the MNA office for more information about volunteering and preserving Michigan’s nature.


To bee or not to bee and the role one invasive plant plays

By Tina Patterson

Spotted knapweed, also known as starthistle, is considered an invasive species in the United States. In Michigan, the eradication of this species has stirred up a controversy between those who want it eradicated and Michigan’s beekeeping industry.

Believed to have first arrived from Europe in the 1800s as a contaminant of alfalfa seed, spotted knapweed survives in dry, sandy soil and most climate conditions. It can be found along roadsides and in former farm fields where it grows in clumps.

Estimated to infest more than 8 million acres nationwide, efforts have been underway in many states to control the spread of spotted knapweed, if not completely eliminate it. This biennial plant crowds out native vegetation and produces a poisonous chemical that deters the growth of other desirable vegetation, like wildflowers and sedges.

Some of Michigan’s beekeepers oppose efforts to control knapweed. Honey flavor is determined by the plant from which bees collect nectar. Because spotted knapweed blooms in late July and early August when many other plants are not flowering, beekeepers count on it to produce the buttery-flavored honey and set up hives near large expanses of knapweed. Considering recent hive collapses, any threat to bees raises alarm for beekeepers. Some worry that if knapweed is destroyed, other more desirable, native flowers will not be as available for nectar and pollen.

However, others argue that diverse natural communities support a range of wildflowers throughout the growing season. Some believe that if natural areas were included in the agricultural landscape that these intact communities could support native bee species of pollinating crops.

Michigan is among the nation’s top honey producers and second only to California in diversity of crops. Some fear that if beekeepers left the state due to knapweed control, the bees needed to pollinate red cherries, apples, blueberries and other crops would have to be imported. This could raise cost to farmers, and ultimately, consumers.

While there are bees at many of MNA’s sanctuaries, knapweed grows at Newaygo Prairie Nature Sanctuary, Karner Blue Nature Sanctuary and Five Lakes Muskegon Nature Sanctuary.

MNA’s policy is to remove invasive species and knapweed falls under that category. However, we acknowledge the concerns of the beekeepers and hope this issue can be resolved.