Eliminating Invasive Plants – Summer Activities

As the seasons change, my management activities change.  Summer is a time to hunt and eliminate invasive forbs and grasses.  Sweet Clover was my initial target several years ago.  As Sweet Clover numbers dropped, I added other species that could be controlled by pulling prior to setting seed.  Now, Yellow and White Sweet Clover, Wild Carrot, Teasel, and Oxeye Daisy are all on my summer pulling schedule.  Not all invasive species can be controlled by pulling.  Sometimes, like in the case of Crown Vetch, the aid of a chemical herbicide is necessary to eliminate the plant.

This is my second year using the chemical Clopyralid in the treatment of Crown Vetch.  Clopyralid kills only broadleaf plants, and is particularly effective on legumes.  Grass is left unharmed, so no bare spots are left in the field after treatment.  The areas I treated this year were fewer in number and much smaller than what I dealt with last year.  Shown above is the largest patch of Crown Vetch I had to spray this year, and it covered only about 40 square feet.

Crown Vetch found its way into my fields as seed that was produced along the edges our township road.  I eliminated the roadside vetch last year, but some of the affected field areas are going to take a bit more work.  Crown Vetch growing beneath the canopy of tall Indian Grass is hard to spot.  The best time to search is when the plants begin to flower.

Unfortunately, peak flowering time for Crown Vetch coincides with flowering of other lavender bloomed plants such as Monarda.  Shown above is Crown Vetch on the left and Monarda on the right.  Colors are almost identical.

Monarda flowers are held above the Indian Grass leaves.  Good luck trying to spot a couple stalks of Crown Vetch hidden down in the grass.

Johnson Grass is another species that requires some herbicide assistance if it is to be eliminated.  I’ve been after this species for several years and only found seven small clumps growing this year.

When dealing with Johnson Grass, I first cut the stalks down to a manageable height and trim back any long, flowing leaves.  This allows me to spray the complete plant with glyphosate, without spraying a lot of neighboring plants.

Johnson Grass is another invasive species that can trace its origin back to the roadside.  Even though the roadside along my property is free of this invasive grass, seed produced along other sections of the road are easily caught and transported by vehicles traveling the roadway.  I expect passersby will replenish my seed supply on an annual basis.

Johnson Grass is hard to miss when it sends up a flower stalk.  This species puts on height in late July, long before the tall prairie grasses, so it doesn’t take much searching to identify new infestations.

When the plant is blooming, tops can be cut and just left in the field.  There is no chance that these flowers will produce viable seed if removed from the plant at this stage.  If treatment is done after seed has formed, it is best to remove the seed heads from the field to eliminate any viable seed being left behind.

I began pulling Wild Carrot six years ago.  I’ve had a lot of success in reducing the numbers of this plant.

Areas that once yielded hundreds of plants, are now producing only a few plants each year.

With fewer plants to pull, I can cover more area.  This is the last of the Wild Carrot infested barrens, an area that I have never had time to get to before.  I was able to finish off this field just as the pulling season came to a close.

Wild Carrot seeds were just beginning to darken during my last week of pulling.  Not knowing if these seeds were developed enough to finish ripening on a pulled plant, I removed the seed heads and bagged them for disposal somewhere other than the middle of my field.

A single Black Swallowtail caterpillar was found on one of the pulled carrots.  I transplanted it to a domesticated carrot variety in my vegetable garden.  It ate for several days and then disappeared.  I hope it went off to find a secure place to pupate. 

Invasive Control - Crown Vetch

I made an effort this year to seek out and spray colonies of the invasive Crown Vetch.  For several years now, I’ve been finding random clumps of this invasive plant scattered about Blue Jay Barrens. 

My efforts began last autumn when I mowed several Crown Vetch infested spots in the field. I returned to those spots in April to spray the early season growth.  I also targeted early season growth between the township road and my field fence.

I elected to use the chemical Clopyralid as a control agent.  Clopyralid is a selective herbicide that targets broadleaf plants, especially legumes.  Unlike glyphosate, which kills all green growing plants, Clopyralid leaves grasses unhurt, so the treated area does not become a big bare spot awaiting the arrival of new invasive seeds.

Within a week, the Crown Vetch was showing the effects of the herbicide.

A month after that, all traces of the invasive plant were gone.

The light colored area in the background at the upper left of the photo is the township road that runs along two sides of a large prairie opening.  A scattering of Crown Vetch plants, remnants of a government funded planting in the early 1980’s, persisted along the shady lane and produced seed that moved with the rain water to establish new plants along the edge of my field.  Hopefully, that influx of seed will now end.

In late May, I found a large infestation of Crown Vetch in a low area that receives runoff water from the road ditches. 

The vetch was growing at a rate slightly slower than its companion prairie forbs, making it difficult to see from a distance.  Fortunately, I was in the area doing some other work and just blundered into the middle of the Crown Vetch patch.  The Clopyralid successfully eliminated the vetch from this site, but it also took most of the other broadleaf plants.  That was a bit of a disappointment, but there was plenty of grass left, so the site was not bare. 

By late June, the Crown Vetch was blooming.  Blooming plants are easy to find and I made sure to search in all places likely to have an infestation.

Crown Vetch is aggressive enough to eliminate all neighboring plants.  By using a herbicide that doesn’t result in the elimination of all species, I have left things in better condition than they would have been if left to the mercy of the vetch.  Crown Vetch increases its growing area by using a technique known as sprawling.  Stalks grow upright by using neighboring plants for support.  Eventually, the stalk overtops the other plants and falls over.  The fallen stalks form a canopy over surrounding plants, causing those plants to suffer from shading and become less vigorous.  The affected vegetation eventually dies and the vetch claims this new growing area.  A single patch of Crown Vetch can eventually cover an entire field.

Most of the Crown Vetch clumps covered less than 50 square feet.  Only one was over 100 square feet.  I’ll have to wait until next growing season to what grows back on the treated sites, but I think the use of Clopyralid has had a positive impact on control of the Blue Jay Barrens Crown Vetch invasion.

Pulling Sweet Clover and Other Invasives

During the time of active plant growth in the prairies, I try to avoid management activities that are likely to disturb the Blue Jay Barrens flora.  Jobs such as mowing or the cutting and dragging of brush are performed during the fall and winter, when the plants are in decline or already dormant.  There are some jobs however, that must be done in the middle of the growing season.  One of those is the removal of Sweet Clover from the fields.

Sweet Clover is a tall growing biennial invasive plant that can overtop and out compete many native species.  This prairie opening was once the site of a healthy infestation of Sweet Clover.  Annual removal of the invasive species prior to seed development has resulted in a site that is almost clover free.

Two species of Sweet Clover, White and Yellow, are found at Blue Jay Barrens.  Yellow is the earlier bloomer, but White is not far behind.  The most effective method I have found of dealing with this plant is to physically pull it from the ground.  Clover pulling season begins around the last week of June and continues into late July.  I search through the open field areas and remove every Sweet Clover plant I can find.  This has been an annual activity for several years and in most locations the clover is present only as widely scattered individual stalks.  It’s fairly easy to move around the field and deal with the clover without trampling too much of the surrounding vegetation.  During my first few years of this activity, the clover was so abundant my trampling gave the appearance that a herd of cattle had run through the field.

I also pull a few other invasive species while targeting the Sweet Clover.  Queen Anne’s Lace is another biennial that can be effectively controlled by annual plant removal.  Some people prefer the name Wild Carrot, but I think that name makes it sound like the plant somehow belongs here.  I prefer a name that reminds of its exotic origin.  Now that the Sweet Clover is so reduced in number, I can give more time to removing the Queen Anne’s Lace.  I also pull Oxeye Daisy from the more established prairie areas.  Older Oxeye Daisy plants, those that have begun to send out rhizomes, cannot be pulled without leaving growing bits behind.  During its first year of growth, the plant is composed of a single stalk and its associated root system and can be removed in its entirety.  Hopefully I’ll be able to stop Oxeye Daisy from moving into new territory.

All of the pulled plants are deposited onto one of the established brush piles.  There’s always a chance that some of the plants have been able to develop viable seeds prior to being pulled, so I don’t leave any pulled plants in the field.  If there are seeds in the bunch, they will fall down through the brush pile and have a very poor chance of ever producing a mature plant.

I was particularly troubled to discover Crown Vetch growing in one of the prairie openings.  Crown Vetch is a notorious invasive plant that was once commonly planted on steep road banks.  The road bordering Blue Jay Barrens was so treated in the late 1970’s and I am constantly dealing with Crown Vetch flair-ups in the fields near the road.  The really disturbing part about finding Crown Vetch in this location is the fact that this opening is far from the road and in a watershed that does not come close to the road.  When an invader comes from an identifiable source and travels a particular route, such as down hill or down stream, you can anticipate where it is likely to occur and plan for those events.  An incursion this far outside the predicted pattern makes me fear that Crown Vetch could be a threat to any part of the property.

Crown Vetch is a perennial plant that can not be controlled by pulling.  The stem has a weak point at ground level that allows it to break away rather pull up the roots.  The roots are left in place to grow a new plant.  This is a common feature of many plant species and allows them to survive in areas that receive heavy grazing pressure.  If this infestation was in an old crop field, I would just spray it with glyphosate.  Being in an area that I consider a higher quality prairie, I didn’t want any collateral plant damage.  I chose to clip the Crown Vetch stalks about an inch above the ground and apply concentrated glyphosate directly to the stump. This is a more tedious process, but the result is the death of the vetch and an unblemished prairie.

Some of the old crop fields, especially areas near the house, present a slightly different set of problems.  There is a point where the quantity of Sweet Clover makes hand removal impractical.  If this little corner was the extent of my management area, I could certainly wade in and pull each one of those thousands of clover plants.  This calls for a different management strategy.  In order to reduce the number of clover plants, the plants must be denied the opportunity to produce seed.  An alternative to pulling the entire plant is the removal of the flower.  I accomplished that task on June 16 by mowing this part of the field.

At the time of the mowing, I wondered how much the clover plants would regrow after being cut.  So far, the clover has failed to return.  The native plants, primarily Indian Grass, are regrowing nicely.  Hopefully, mowing will bring the number of Sweet Clover plants down to a more manageable level.

I’m always watchful of biological controls that may be working on invasive plants.  This handsome caterpillar was busy munching away on one of the Yellow Sweet Clover plants.  I identified it as the larva of the Hitched Arches moth.  It appears that this moth eats a wide range of plant species and is not a super Sweet Clover predator.  It may not help me with my task, but it was nice to share the field with this small helper.

New Crown Vetch Infestation

A little foray through the field turned bad when I found a Crown Vetch blossom in my path. Crown Vetch was once planted on steep banks and other hard to maintain areas for erosion control and wildlife habitat. Having had some little success in that role, it went out on its own and made a name for itself as a non-native invasive species. It’s not a plant I want growing at Blue Jay Barrens.

It starts innocently enough with a few shoots coming up through the existing vegetation. Its sprawling growth habit will soon cover and then smother the neighboring plants. The takeover is not rapid, so it may be several years before it becomes obvious that the plant is a problem. By that time it’s so well established that its removal becomes a very complicated process.

The most troubling facet of this new infestation is its location. The new plants are growing right in the middle of the field. There are other patches of Crown Vetch growing at Blue Jay Barrens, but they are all near the road where they had been seeded in an attempt to stabilize steep road banks. The embarrassing thing about that is the fact that the agency I work for funded the seeding through a cooperative agreement with the County. It all happened over 30 years ago and it’s not something we would do today, but the locations of Crown Vetch infestations moving into my fields match exactly those of the seeded road banks. I guess that’s the cost of an education.

Crown Vetch is a legume with a flower cluster resembling that of White Clover. Its ability to utilize atmospheric nitrogen gives it an advantage on poor soils. The plants that it kills fall to the ground and decompose to release nutrients that are used by the vetch. It flourishes under these conditions. A solid mat of vetch plants eventually develops and little else will be found growing there.

There were few enough plants in this spot that I could probably have pulled them all and eliminated the stand. I would have done that, but I was afraid the plants had produced seed in earlier years. Crown Vetch is a prolific seed producer and seeds in the ground will germinate and continue the infestation. I chose to spray the patch with glyphosate. This will kill all plants growing on the site and will produce a bare spot that will make it easy to spot any emerging Crown Vetch seedlings. The dead spot will be small enough that neighboring plants will quickly fill it in. While that’s happening I can keep an eye on things and make sure that it is clean of vetch.

Crown Vetch

The mowed fields are growing rapidly and I’m enjoying the opportunity to observe the growth without it being covered by dead stalks and leaves. I’m seeing a lot of plants that would normally be missed, some of which are not a pleasant sight. I found another invader adding its green to the landscape.

This is Crown Vetch, an invasive legume that has been commonly planted along the roadsides to help control erosion. This county had a program about 30 years ago that seeded many miles of roadside Crown Vetch. Unfortunately, the plant does not stay put, and has moved off the roadsides and across the adjoining fields. It can quickly eliminate competition through shading and will produce large, dense mats of vetch.

It’s odd how many of our most aggressive invasive plant species were once considered valuable conservation plants that any conscientious landowner would find a place for. Multiflora Rose, Autumn Olive, and Bush Honeysuckle were all widely distributed and recommended as conservation plants and are now categorized as noxious invasive species.

Roads are incredibly effective at allowing seed to move long distances and colonize new land. If you’ve ever coated your vehicle with dust from a gravel road, you know how easily something on the road surface can be attached to your car. Every time I pull off the side of a narrow road to allow an approaching car to get by, I wonder what I might be picking up in the tires to take home with me. Even the rush of air created by a passing car can move seeds along.

My fence does a good job of keeping out stray cows and 4-wheelers, but not plants. This road was not a part of the Crown Vetch planting program. An intersecting road was a program participant and is probably the source of my infestation. This is yet another plant I’m going to have to battle in order to protect the native plant population.