Control Techniques

The youtube video by the National Park Service in Maine does a great job discussing the alternatives. In our workshop, we will focus on 2 techniques, critical period cutting / defoliating and cut stump using herbicide.

When working on your own property, you should decide which of the available options is right for you and your project. 

While the control techniques for each type of invasives are generally the same, it is important to review the species specific information to verify before starting work. A general rule of thumb is that when Mother Nature is involved then there are always exceptions. A few examples:

• Woody - Tree-of-Heaven - The recommended approach is to use basal bark herbicide. With this species if either cut stump or critical method cutting are utilized, the roots “freak out” prior to the herbicide being effective and the roots send up many shoots.

• Common Privet - The recommended approach is to leave cuttings on the ground. With privet, cuttings can reroot if there is enough ground contact and moisture.

When to use this Method:

• You have the appropriate tool for the size plant to be pulled.

• Manual pulling (by hand, with a shovel or a weed wrench) is much easier after a rain.

• Be careful to not create too much solid disturbance that can allow the seed bank to start.

• For larger plants, a tractor can be used but there will be significant solid disturbance

• For areas where large invasive plants have been removed, there can frequently be many seeds in the seed bank that for the first time get sun and sprout. It is much easier to pull these plants when they are small.

When to use this Method:

• You’re trying to remove buckthorn with stems greater than 2” in diameter (smaller stems can be tricky to carry out)

• You're working on a small natural area or a home landscape

• You don't want to or can't use herbicides

• You can commit to following up consistently for at least two full growing seasons

*Note: You can also start this process with step 1 in mid-September, then step 2 in late May or early June and so on, flipping the spring and fall tasks. Roth, Lee - fmr.org/CPC

Specific Steps for Success

1) Cut and strip the main stem (year 1, late May or early June*)

Cut through the buckthorn's main stem 3-5 feet above the ground, then cut off any side branches or additional growth on the remaining stem. The goal in this first step is to remove a buckthorn plant's entire "canopy," which works best once buckthorn has fully leafed out and expended its stored energy reserves to create the season's new growth. Without leaves, the buckthorn plant cannot photosynthesize — its only method to replenish those stored nutrients. You'll want to use a saw for the main stem, but you may be able to strip side branches with loppers or pruners.

2) Re-strip the stump until it's bare (year 1, mid-September*)

Cut off, or "re-strip," any branches and new growth from the tall stump using loppers or hand pruners. Cut as close to the main stem as possible. Since you're leaving the main stem intact, this step is better described as re-stripping than re-cutting or applying a second cut. Re-stripping stresses the plant by continuing to exhaust its root reserves and preventing it from drawing down any additional nutrients it may have gained in its leaves throughout the summer. 

3) Re-strip the stump again (year 2, late May or early June*)

Repeat the re-stripping process after initial leaf-out in the spring, using loppers and pruners to remove all new growth and anything you missed the previous fall. The goal is to leave a bare main stem. This repeated stressing of the plant, combined with a lack of stored energy from the previous year, brings about the decline of the buckthorn. Depending on site conditions like soil nutrients and light availability, the stem may already be dead.

4) Re-strip the stump one more time (year 2, early to mid-September*)

Do one final re-strip before leaf-drop in the fall. This round should fully exhaust any stored energy reserves and will put an end to the plant without the use of herbicides.

5) Remove the stump (year 2, fall, or year 3, spring)

Buckthorn is relatively shallow-rooted, so in most cases, you can just push the stump over. Try not to disturb the soil too much; tamp down soil and leaf litter to prevent exposed soil, which can give way to erosion and new weedy species. If the plant is not yet dead, continue the re-stripping process over the following growing season.

6) Seed and plant native species (years 1 and 2)

Removing buckthorn is only half the journey toward restored habitat. Seeding and planting native species restores wildlife resources and provides competition for new buckthorn seedlings. If you're planning to seed with native species, wait until the late fall of the first year. This step can also be done in the fall of the second year. You can plant new shrubs in the spring or fall of the second year, as long as they don't hamper your ability to continue manipulating the buckthorn stems. Great woody native replacement plants for buckthorn in forested areas include: highbush cranberry, nannyberry, chokecherry, gray dogwood, pagoda dogwood, American hazelnut and serviceberry.

7) Pull nearby buckthorn seedlings and young growth + tend new plantings each year (ongoing)

The big buckthorn plant you removed could have created hundreds of seeds through prior years' berries. Those seedlings will probably continue to come up for a few growing seasons. To deal with this new growth each season, pull up the small buckthorn plants and their roots by hand. Replace any soil that gets disturbed in the process. Make sure to water and tend to any new plantings.

This method follows the same events and timing as the critical period cutting.

The exception is that instead of cutting down the invasive plant, a saw is used to girdle the plant

Because of the girdling aspect, this method is better for plants that are 2 inch diameter or larger

It is critical that the girdle completely circles the tree and that all of the nutrient flow is cut off for the girdle to be successful. 

This is a new technique which hasn’t had any peer reviewed publications on the effectiveness.

Key steps:

1. • Cut the bush down to a small stump

   • Heavy black plastic is placed over the stump and secured with zip ties. 

   • It is important that the black plastic goes to the ground and prevents sunlight from getting to any resprouts

   • After the roots have died (a few years), the baggies should be removed

Buckthorn baggies

TBD

This method applies a 6 to 12 inch band of herbicide around the circumference of the trunk of the target plant, approximately one foot above ground. 

The width of the sprayed band depends on the size of the plant and the species’ susceptibility to the herbicide. The herbicide can be applied with a backpack sprayer, hand-held bottle, or a wick. 

Ester formulations of herbicide are usually best for basal bark treatments, as esters can pass most readily through the bark (as compared to salts). Esters can be highly volatile; however, so basal bark treatments should be performed only on calm, cool days. During summer, treatment is best carried out in the mornings, which tend to be cooler. 

The basal bark treatment works best on young trees with smooth bark. It is usually not effective against older plants with thick corky bark.

The girdle method, also called the “frill” or “hack and squirt” treatment, is often used to treat woody species with large, thick trunks. The tree bark is cut through using a handsaw or chainsaw. The tree is not cut down. 

Ensure the cut completely encircles the circumference of the trunk. 

Herbicide is then immediately applied to the cut with a backpack sprayer, squirt bottle, syringe, or similar equipment. Because the herbicide is placed directly onto the thin layer of growing tissue in the trunk (the cambium), an ester formulation is not required. The herbicide is drawn into the cambium layer of the plant and disrupts plant growth.

Use the drill treatment rather than cutting for trees with DBH (diameter at breast height) greater than three inches. 

Drill one hole for each inch in DBH. (A ten-inch DBH tree would require at least ten holes.) Holes should be drilled at a slight downward angle to prevent the herbicide from running out, and should be deep enough to penetrate the inner bark or growing tissue, but not too deep so as to damage the standing integrity of the tree. 

Holes should also be staggered to help prevent the tree from being damage to the point where it could fall. 

Herbicide is then immediately applied to the hole with a backpack sprayer, squirt bottle, syringe, or similar equipment.

This method is often used on woody species that normally re-sprout after being cut.  Cut down the tree or shrub, and immediately apply herbicide on the exposed cambium (living inner bark) of the stump. The herbicide must be applied to the entire inner bark (cambium) within five to ten minutes after the trunk is cut (if using glyphosate). The outer bark and heartwood do not need to be treated since these tissues are not alive, although they support and protect the tree’s living tissues.

This technique should NOT be used in the spring when a plant’s sap is rising, because the herbicide will not be transported to the roots well at this time (this is species specific, but is a good rule of thumb).  

Herbicide can be applied to cut stumps in many ways, including spray and squirt bottles, or even paint brushes. Care must be taken to avoid applying too much herbicide, and allowing it to run-off the stump and onto the ground. Herbicide can also dribble from bottles or brushes and fall on desirable plants or the ground. 

The cut stump treatment allows for a great deal of control over the site of herbicide application, and therefore, has a low probability of affecting non-target species or contaminating the environment. It also requires only a small amount of herbicide to be effective.

This method is used most often as part of an integrated approach. Rarely will mowing or cutting effectively control invasive species in isolation. The primary purposes of cutting or mowing are to reduce the above-ground biomass or to stop a species from going to seed. 

A mower can be as simple as a basic lawn mower all the way to a tractor and industrial-strength brush-hog. For cutting, a weed-whip or brush-cutter is recommended. A weed-whip is a light-duty often gas-powered implement with a high-speed rotating plastic wire, which cuts grasses and flowers well. A brush-cutter is heavy duty and is intended to cut small woody shrubs. It is useful for infestations of small woody invasive species (follow-up is required).

It is importance to understand plant physiology when considering mowing or cutting. Infestations of certain plants can be exacerbated when cut. Improperly applied or timed cutting can spread the target invasive species (for example, mowing a small autumn olive bush when it is laden with seeds). This also applies when using handsaws or loppers.

Repeated mowing can eventually control woody invasive species, as many woody species are mowing intolerant. Mowing in late spring, after the woody plants expended energy to grow leaves, is effective at setting back the plant. A second mowing in the late fall, before seeds set, also keeps the plant from reproducing.

Foliar Application – General Considerations

These methods apply herbicide directly to the leaves, stems, or cut surface of a plant. An adjuvant or surfactant is often needed to enable the herbicide to penetrate the plant cuticle, a thick, waxy layer present on leaves and stems of most plants. Ask participants to define an adjuvant or surfactant. An adjuvant is an additive to improve herbicide effectiveness. A surfactant is an adjuvant that helps break the bonds of the mixture to better spread the mixture across the leaf/stem. In effect, a surfactant “Makes water, wetter”.  There are several types of foliar application tools available. Ask participants to name a few. 

You will be surprised at the amount of drift that can occur from a sprayer. This causes the potential for damage to non-target species. Participants and managers will need to consider weather conditions and timing of the foliar treatment. You’ll cover this in more detail shortly.

When the weather is either too hot or too cold, the efficacy of the foliar herbicide application can be reduced. As a general rule, when the temperature exceeds 90°F, a plant will close the small pores (stomata) in the surface of leaves and stems to conserve water. The amount of herbicide taken up by the plant will be reduced. At the other end of the range, when the temperatures drop below freezing the plant reduces cellular activity and herbicide efficacy is reduced. It is important, however, to communicate to participants that this is highly variable and changes for different species and sites. 

In some circumstances, foliar application during dormancy of native plants is preferable because it reduces the likelihood of damaging other non-target plants. Share the following example with participants: You can treat buckthorn late in the fall after other native shrubs and grasses have senesced for the winter. This will ensure that non-target damage to other plants doesn’t occur because they haven’t yet emerged. Garlic mustard is a plant that stays green throughout the winter, which means treatment can happen when the rosettes are exposed. 

Spray Drift Precautions

Take precautions to avoid damage to off-target plants by adjusting spray pressure. Generally, it is recommended to use low-pressure spray combined with large droplet size (sprayers can be adjusted from fine to coarse spray droplets). High-pressure spray combined with small droplet size increases the distance spray will drift. High-pressure spray can be used effectively when treating large monocultures where the risk to off-target species is low. Wind-speed will influence spray drift; higher the wind-speed, the greater the drift.

General Spray Technique

• First, figure out the dominant wind direction. You’ll want to keep the wind behind you.

• Start at the downwind end of the area to be treated.

• Treat in lines that are perpendicular to the dominant wind direction, which allows you to always be spraying with the wind at your back.

• It is helpful to mark the end points of each spray line to help keep you oriented. It can be difficult to keep track of where you’ve treated and where you need to cover. You can use existing trees or landmarks, or you can mark spray line ends with a flag or marker tape.

• Work your way back and forth along the spray lines from the downwind to upwind ends of the treatment area.

Grid and Spray Technique 

It can be difficult to keep track of where herbicide has been sprayed and where it has not. Use the grid and spray technique to help treat areas with moderate to heavy infestations, whereas spot treatment is better for light infestations. This is a technique where individuals treat areas within their spray wand range and move in conjunction with other individuals through a treatment area. Walk participants through the steps on the slide.

“Glove of Death”

Herbicide is sprayed directly onto a heavy cotton glove worn over a thick rubber/latex (or nitrile) glove. Wearer of glove can then apply the herbicide with total precision and little or no runoff

Requires Special training and approval

Frequently doesn’t get hot enough to kill larger woody plants