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The Threat of Swallow-wort

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Most of the calls that we receive for hay usually ask if we have no alfalfa in our hay. Alfalfa is a concern for many horse owners, as some horses cannot tolerate its richness. But, have you ever wondered what else might be in your hay?

As stewards of the land, we walk our fields every spring and after every cutting to see what is trying to make its home in our fields. We keep current on both toxic and invasive plants and follow the recommendations of Michigan Extension to keep them in check. The latest concern in our area – Rose Township – has been the invasive species – Swallow-wort. There are two variations of this plant – Black Swallow-wort and Pale Swallow-wort.

Black Swallow-wort

black-swallow-wort

The Black Swallow-wort is a perennial vine that can grow up to 7 feet. The purple flowers are star-like and are in clusters of 6 to 10 flowers. The seed pods look like smaller milkweed pods.

 

Pale Swallow-wort

pale-swallow-wort

The Pale Swallow-Wort is also a perennial vine that can grow up to 7 feet – but this vine is twining – which means it can wrap itself around other plants, fences, even trees. The pink flowers are star-like, but narrower than the Black Swallow-wort flowers. They are also in clusters of 6 to 10 flowers and produce seed pods like the milkweed.

 

Impact

In addition to being considered an invasive species, both types of swallow-wort are noxious plants. The roots of these plants are poisonous to livestock. This includes horses as well as cattle. The plants are poisonous to the Monarch butterflies. It’s important to note that most cattle and horses will not eat the roots of a plant unless it has been uncovered or otherwise disturbed. At this time, there is no warning about the flowers, vines, or seed pods being toxic to horses or cattle.

The twining ability of the Pale Swallow-wort gives it the ability to smother other plants in the area, similar to the way wild grape vines have destroyed forests when left unchecked. The Black Swallow-wort spreads through the area chocking out other plants by blanketing the area.

Both plants are spreading throughout the United States.

Black Swallow-wort distribution map

 

Control and removal

The most effective way of controlling this plant is by spraying it twice a year. Once in June when it is flowering, and again in August. According to the study, after two application with glyphosate less than 5% of the plant was present. After two applications with triclopyr less 15% of the plant was present.

If using an herbicide, be sure to add am adjuvant to the solution. The vines and leaves of the swallow-wort are waxy and without the adjuvant, there will be no penetration into the plant.

Clipping and destroying the pods will keep the plant from reseeding itself, but will not keep the plant from growing.

It not advised to cut or mow the plant itself. This will only stimulate the plant to grow denser the following year. Most of the plant growth comes from the crown of the plant or the rhizome. If you want to remove it completely without using a herbicide, you would need to dig the plant up completely. Plowing it under will only divide the crowns or rhizomes and increase its density.

Even a prescribed burn is not an effective means of controlling this plant.

Two leaf-eating moths have been identified as another possible resource, but there hasn’t been enough research or trials run to ensure that this method won’t become a problem once the swallow-wort has been eradicated.

Replanting an area with native grasses or other grasses to thwart the regrowth of swallow-wort is recommended.

State or other agency assistance may be available but they have to be made aware of the problem before they can act. Michigan Invasive Species Information Network (MISIN) (http://www.misin.msu.edu/) is an effort led by researchers with Michigan State University Department of Entomology. When I added my two sightings to their database, I noticed that no one from Rose Township has made an entry since 2012 when the last epidemic of swallow-wort was of concern. Yet, I hear people in our community discussing the threat without taking any steps to remedy the situation.

Prevention

You cannot stop the wind from blowing the swallow-wort seeds into your area, but, you can be a steward of your land by checking the areas where these plants would be most likely to grow. Treat the plant with one of the proven methods to prevent its spread.

Make your neighbors aware of the plant if you see it on their property.

Report any sightings to MISIN (http://www.misin.msu.edu/) or your state agency for invasive plants.

If you hike, ride, or otherwise find yourself in an area where swallow-worts are growing, brush off your clothes, vehicle, or anything else that might be carrying the seeds back to your area. We remove all debris from our farm equipment before it leaves the field to ensure that we are not moving any plants to the next field.

Being vigilant is everyone’s responsibility.

 

Resources

Stewardship Network – http://www.stewardshipnetwork.org/sites/default/files/acwmaforswallowworti_05092012/index.html

Invasive Treatment –https://mnfi.anr.msu.edu/invasive-species/Swallow-wortBCP.pdf

Adjuvants for Enhancing Herbicide Performance – http://extension.psu.edu/pests/weeds/control/adjuvants-for-enhancing-herbicide-performance/extension_publication_file

Michigan Invasive Species Information Network – MISIN – http://www.misin.msu.edu/

KeiLin Farm, a producer of farm fresh beef and eggs, as well as premium hay, is located in Rose Township, Michigan and is in the process of acquiring the required licenses to become a small wine maker.
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