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. 

Far East Field

This is a good time of year to visit areas to assess management success and future needs. I’m in year one of my five year management plan renewal, so I’m identifying activities that should be accomplished within the next few years, as well as those things that urgently need to be completed during the coming winter. This field is roughly four acres in size. It was last cropped around 1976 and was being used for hay when we bought the property. Bedrock is shale and the pH is low throughout the entire soil profile. It has an amazing amount of diversity for such a small field. Wet conditions at the low side of the field transition to super dry conditions as you travel up the slope toward the high ground.

Encroaching woody growth was cut out of this field two years ago. This Tuliptree probably got missed when I was marking the cut trees for herbicide treatment. Multiple sprouts have created a thick bush in place of the single trunked tree. This definitely needs to be cut this winter.

The majority of trees in the field are ones that I have purposely left in place. These are White Flowering Dogwoods. Disease eliminated the dogwoods from their rightful place in the woodland understory. In order to keep White Flowering Dogwoods on the property, I’ve allowed them to stay in the fields. They’re spaced far enough apart that they don’t hinder growth of the prairie species.

The township road boarders the long side of the field and makes this a likely place to discover non-native invasive species. I found just a few Johnson Grass plants near the fence. These must have been too small for me to notice when I did my normal Johnson Grass search earlier in the year. Since they would have been difficult to spray without killing everything around them, I just pulled them up. I’ll check this spot more closely next year to see if I can catch the plants when they’re smaller.

From the looks of the roots, these are probably young plants that came up from seed this year. That’s why they weren’t noticeable earlier. Johnson Grass spreads by way of rhizomes, so it’s hard to control the plant by pulling. Any bit of rhizome left in the soil produces a new plant. Most of the plants I pulled had not yet begun to form rhizomes and showed no signs of having arisen from an established rhizome. The plant second from the left shows some rhizome development and had a break showing that it had left something beneath the surface. Pulling may not have eliminated the infestation, but it certainly thinned it out. If you can’t kill an invasive plant outright, the next best thing to do is cause it severe stress.

The Dwarf Sumacs are bowed under the weight of some tremendously successful seed heads. One more growing season and they’ll reach the stage where they must be cut back to the ground.

There are three large Virginia Pines in this field. Their shade does suppress some prairie growth around the base of the trunk, but they add a bit of diversity that is worth the loss of a few sun loving plants. They’re really turning into some lovely trees.

Several of the Butterflyweeds are blooming here. Unfortunately, there are virtually no swallowtails or other large butterflies to take advantage of the flowers. This has been a dismal year for large butterflies.

This caterpillar is evidence that a Monarch butterfly did come by. I’ve seen scattered Monarchs, but I think they all moved north as quickly as possible. The reports from farther north indicate an abundance of Monarchs up there. I’m looking forward to a very impressive southern migration this fall.

Wild Senna is scattered across the field. All were developing an impressive set of seed pods. It’s amazing how quickly this plant has spread during the past few years.

The bulk of the field is open and developing into a fine prairie. There are a few woody plants that need to be removed and a minor need for some invasive plant control, but there are no big problems to deal with. In a few years, this field should need nothing more than occasional maintenance.

Johnson Grass

There are some plants that are recognized by many people as being noxious weeds. One of those is Johnson Grass. These towering grass plants with their broad strapping leaves are a major weed of agricultural fields and cost farmers a lot of money each year in spray costs and loss of production. Seeds travel widely in flood water and as passengers on farm machinery. If you are trying to convince people that management for native plants is a proper thing to do, you definitely don’t want such a well known weed growing where everyone can see it. I battle with this plant every year and most of my trouble is within sight of the road. New seed is regularly deposited on the roadside by farm equipment, road maintenance equipment and vehicles that snag plants crowding the edge of the road.

The origin of one patch of Johnson Grass is something of a mystery. It’s a fairly new infestation, but it’s nowhere near a road. It sprang up on the site of a patch of Poison Hemlock that I eradicated several years ago. The hemlock is now gone, but Johnson Grass has taken its place. I know that the bare ground resulting from the loss of the hemlock was perfect for colonizing Johnson Grass, but I don’t know where the seed came from.

Fortunately, Johnson Grass is not found in the established high quality prairies, so I don’t have to worry about protecting rare plants when I go after the weed. An easy way to destroy small patches is to mow the grass in late July, wait for the grass to shoot back up and spray it with glyphosate herbicide.

Johnson Grass regrows much more quickly than most of the other plants, so it’s possible to spray the site without killing everything else. Even if everything else dies, that’s better than letting the Johnson Grass live. In the thickest patches of Johnson Grass, there’s really not much else growing anyway.

For patches this size, I use a backpack sprayer with a flat fan spray nozzle. This gives good coverage on the target plant and makes for a more controlled placement of the herbicide. That spray wand looks like the heat ray weapon on the Martian flying machines in the original War of the Worlds movie. Maybe if I dye the spray red, it will give the plants more of a scare.

Johnson Grass

This tall grass is Johnson Grass, Sorghum halepense, which is legally defined as a noxious weed in Ohio. It is primarily a problem in crop fields where management techniques reduce competition from other plants. New colonies of Johnson Grass usually occur along the road from seed dropped by vehicles, especially farm equipment, contaminated by seed picked up at another location. Established prairies can often hold their own against Johnson Grass, but it’s best not to let a potential problem get started.

These open panicles are easy to spot atop the tall Johnson Grass plant. Many people think of my prairies as giant weed patches, so I aggressively try to eliminate plants like this that many people can positively identify as a weed. Normally I spray these plants early in the season before they can produce a flower head, but the threat of rain seemed to appear every time I could schedule time for this task.

Once these plants are tall enough to flower, spraying becomes an unsatisfactory method of control. Trying to spray such a tall plant results in a large kill radius and the loss of too many desirable plants in the surrounding area. My fall back strategy is to pull the plants. Pulling is not as effective as spraying because of the plant’s habit of spreading by way of rhizomes. Rhizomes left in the soil after the plant is pulled will survive and produce new plants. Fortunately I have been dealing with these plants for many years and am not working with established colonies. The young plants that I am pulling have not had a chance to produce many rhizomes and older plants are severely stressed when pulled.

These plants have been pulled before seed could begin to develop. Pulling plants that have already produced their crop of seeds results in those seeds being scattered even more than would have occurred if they had been left alone.

Not taking any chances that either early developing seed or hearty rhizomes are left in the field, I’ve carried the pulled plants and piled them in my garden. The organic material will help the soil and no seeds or plants will have a chance of surviving here. New Johnson Grass infestations will continue to occur along the road, so my involvement with this plant will never end.