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.