Eradicating buckthorn (Rhamnus cathartica)

Buckthorn infestation in a natural area in late fall. This species retains its green color long after all native species have senesced and turned brown. At this time of year it is very easy to detect.

Buckthorn seedlings coming up in an area where a large infestation had been cleared the previous winter. The seed bank can be quite prolific.

Pulling buckthorn plants does not eradicate an infestation It is virtually impossible to pull up all of the tangled underground plant mass of a buckthorn stand. The following year new shoots arise and reinitiate the infestation.

Fire does not eradicate buckthorn plants. Buckthorn plants are not eliminated even by annual burning. All fire does is top-kill the shoots. Numerous dormant buds then begin to grow and send up stems. In some cases, as many as a dozen new shoots can arise from a single root collar. It is possible that in restored prairies, where much hotter fires occur and tall grasses and forbs shade the soil, that buckthorns will be outcompeted, especially if the prairie is burned every year. However, in savannas and open-oak woodlands, where buckthorn infestations are most common, hot fires are less common and most of the understory plants are not tall grasses.

Girdling does not eliminate buckthorns. Although several weed manuals prescribe girdling as a method to eliminate buckthorn, this is completely ineffective. The following year there will be numerous shoots arising from the area below the girdle. Buckthorn plants have numerous dormant buds just waiting for the elimination of apical dominance.

Herbicide treatment is essential for eradication of buckthorns, but not all herbicides are equally effective.Glyphosate is effective in killing seedlings or small resprouts (foliar spray at 2-4% concentration). It is also effective for cut-stem treatment of large buckthorn shrubs, but glyphosate is less effective in treating small cut stems. Garlon 4 in oil should be used; treating not only the cut surface but dribbling herbicide down the side of the stem (basal bark treatment). Probably because of the massive root mass, getting the herbicide to the critical parts is impossible if herbicide is only dabbed on the tiny cut stem.

The leaf spritz method A very effective method for control of leafy buckthorn stems from mid summer until early fall is the leaf spritz method. This involves using a hand spray bottle containing 20% Garlon 4 diluted in bark oil. Two or three of the upper leaves on each buckthorn stem are given brief "spritzes", so that the herbicide spreads out on the leaves. Within a few days the stem will be visibly damaged and within a week will be dead. This technique is very benign to surrounding native plants, as the herbicide is confined to the upper area of the buckthorn plant. Since small buckthorn plants generally consist of multi-stemmed colonies, it is essential that "all" stems are treated.

Buckthorn stem that had been spritzed with Garlon 4 in oil a few days before. When done in mid-summer, when buckthorn is growing rapidly, this treatment usually results in death of the stem within a week. It is essential that all stems of multi-stemmed buckthorn plants be treated.

Extensive resprouting around a buckthorn cut stem that had not been treated with herbicide.

Note that it is essential to follow-up the buckthorn control in future years be done, since there will almost certainly be resprouting from dormant root masses.

The key to eradication of buckthorn is a combination of methods:

• Remove large buckthorn plants by cutting and basal-bark herbicide (Garlon 4) treatment, or by basal-bark treatment alone. Large plants that have been basal-bark-treated without cutting die in the first growing season and fall over in a few years. Cutting without herbicide treatment is worthless and pulling or digging will not remove all of the root mass from the soil.

• Buckthorn eradication is a multi-year task. Follow-up treatments of all areas of infestation must be made.

• Monitor the site carefully for the new seedlings that will inevitably arise from the seed bank, and immediately foliar spray with triclopyr (5% Garlon 3A). Plants should be sprayed in the spring, as soon as they are visible (around mid-May in our area). Glyphosate is also effective as a foliar spray at 2-3% concentration, but is not advised for use on cut stems.

• Carry out controlled burns only after all plants have been cut and treated or foliar sprayed. Burning before herbicide treatment should not be done because all it will do is top-kill, and there will be no living stems left to transport herbicide to the roots. Also, burning will only result in resprouting and the formation of many stems where one was originally.

There are at least three periods of the year when buckthorn control is recommended..

• Late May after spring burns, when backpack sprayers can be used to treat small buckthorn resprouts with foliar Garlon 3A.
• Mid to late summer. This is the time of year when buckthorn leaves are at their maximum height and the leaf spritz technique works great. Spritzing just two or three of the upper leaves from a hand spray bottle is all that it takes to kill a stem. (See this link for more detail.)
  
• Mid-October to mid-November when using basal bark treatment with Garlon 4.

Honeysuckle (Lonicera sp.)

There are several species of bush honeysuckle that cause problems in our area, including Lonicera morrowii, L. maackii, L. tatarica, and the hybrid Lonicera X bella. However, there is no reason to attempt to distinguish them since they are all nonnative and they are all bad. The native honeysuckle in our area (Lonicera reticulata and L. dioica) can easily be distinguished from the bad ones because the natives are all woody vines rather than bushes.

Honeysuckle bushes invading a natural area. Photo taken in early spring when the plants are just leafing out.

A honeysuckle is a multiple-stem bush. After cutting, it is essential that all cut stems be treated. Adding a red dye to the herbicide is a good way to ensure complete treating. When using a hand loppers, count each stem as it is cut and count again as they are treated.

Foliar spray with glyphosate works very well with honeysuckle in the fall of the year, after all the native vegetation has senesced. Timing is a little tricky, and years will differ. It is also advisable to use a higher concentration of glyphosate (8-10% active ingredient). The blue dye permits monitoring the efficiency of the spraying.

The term "bramble" refers to a whole group of plants of the genus Rubus, which include blackberry, red and black raspberry, and dewberry. Brambles are a minor component of the degraded savanna, but once the habitat is opened up and light reaches the forest floor, brambles can grow rampantly. Although our brambles are native, we still consider them undesirable because they tend to take over the savanna.

Patch of black raspberry (Rubus occidentals) in a restored bur oak savanna.

Brambles are biennial plants but have a perennial root system. The roots continue to grow for the life of the plant, but new above-ground shoots (generally called "canes") develop each year. The first-year shoots grow vegetatively but do not flower. In the second year these shoots flower, set seed (berries), and then senesce and die.

The underground system of a black raspberry plant.

Right. Bramble resprouts developing from a clone that had been top-killed by fire. Control is possible by foliar spraying with triclopyr early in the spring, when the rosettes are still small.

Bramble patch burning during a savanna burn. The principle fuel is oak leaves, but the leaves of the brambles themselves also burn. Brambles are very sensitive to fire and top-killing is usually virtually complete. The resprouts that arise the following spring (see photo above) should be sprayed with triclopyr.

Invasive weed control in savanna restoration

Below is a list of invasive forbs or grasses that are often experienced in savannas. No savanna would ever be expected to have all these weeds, but three or four might be expected. Weeds that are found predominantly in wet and wet-mesic areas are not included.

In contrast to shrubs, weeds are less a problem in savanna restoration, but if one of the above becomes established, especially those that are perennials, immediate attention to eradication is strongly advised, and herbicide use should not be slighted.

Possibilities for control of weeds is related to their annual growth cycle.

Annuals do not normally need to be controlled, although heavy infestations might be mowed to keep the keep them from going to seed.

Biennials are not generally controllable in their first year of growth, when they are often difficult to find. However, they can be foliar sprayed with glyphosate in the late fall/early winter of their first year, when they remain green long after the native vegetation has senesced. In their second year, biennials are best eradicated by hand pull (or digging). However, heavy infestations which are too costly to hand pull can be mowed at the time of peak flowering but before seed set has commenced. Herbicide use is not recommended in natural areas such as savannas unless there is no "good" native vegetation.

Perennials must be controlled by herbicide. It is virtually impossible to eradicate perennials by digging or pulling, since not all of the root mass will be removed. Mowing is completely ineffective for the same reason. Spraying can be done in the early spring, when these exotics are usually up and thriving but before the native species have come out of the ground. Spraying can also be done in the late fall, when these exotics remain green and the native species have senesced. In the summer, they may also be mowed at the time of early bud stage and the resprouts sprayed about a month later.

Despite the recommendations of some weed manuals, perennial weeds can almost never be eradicated simply by mowing, unless the mowing is as frequent as that used for lawns.

For tall perennial weeds such as Canadian thistle, or native invasive forbs like Canada goldenrod or woodland sunflower, a suitable approach is to mow the infestation at the early flower bud stage, and then spray with herbicide the regrowth some weeks later when it is at about the six-inch height. For thistle and other species of the Compositae, the herbicide of choice is clopyralid (see above).

Shovels for weed removal

Weeds can generally be pulled by hand, but sometimes a shovel is necessary. Nick Faessler of the Prairie Enthusiasts has devised and sells (through the Prairie Bluff chapter) a very handy shovel. He calls it a Parsnip Predator, because he devised it for control of wild parsnip (Pastinaca sativa). However, it works for sweet clover, bull thistle, Queen Anne’s lace, and lots of other invasive plants of natural areas. The narrow profile of its blade means that adjacent “good” plants are left alone.

The sale of the Predator is a fund raiser for the Prairie Bluff folks, and it can be purchased on line. Copy this link and paste it into your browser: http://www.theprairieenthusiasts.org/chapter/pbluff/PARSNIPP.htm

A homemade version can be made a little cheaper, but you have to have equipment to cut the blade down. If you only need one, I’d go with the Faessler version.

A home-made Parsnip Predator. The narrow end of the shovel causes less soil disturbance and makes digging the weed easier. The tip of the shovel should be kept sharpened.

Management of a weed removal activity

A systematic approach to weed removal is recommended. The area should be divided into manageable units and the worker or group of workers moves along, keeping a sharp eye out for undesirable plants. Each worker carries a shovel, although if the weed can be hand pulled, this is usually quicker and requires less effort. A recent rainfall often helps to make the weeds easier to pull. Set up swaths such as described above for shrubs.

Since each weed has its own season, the site must be traversed several times during the growing season. Local experience will be important in deciding when and how often the site should be surveyed.

If the target is a perennial and herbicide is to be used, a similar systematic approach should be used, with each worker having a backpack sprayer with appropriate herbicide. A blue dye helps to ensure that each plant is sprayed (and that a plant is not sprayed more than once).

Weeds of special concern

Sweet clover
Two biennials on the above list often become problems after burns: white and yellow sweet clover. This is because the seeds of these species are able to remain viable for long periods in the soil, and fire stimulates them to germinate. Thus, the next year after the first good fire, first year plants appear, often in large numbers. The following year, major infestations of second-year plants develop, which must be dealt with immediately. If these two species are not controlled, the second-year plants will set seed, and you will be back to square one. Because the first-year plants remain green into the late fall/early winter, they can be sprayed with glyphosate at that time. Although this will not kill all the plants in the infestation, it will make a major impact.

Garlic mustard and Japanese hedge parsley are two species from the above list thrive in shady woodland areas and will also grow in savannas. These can be controlled by late fall/early winter spraying of first-year plants, spring spraying of second-year plants, and hand pulling all plants missed by the spraying regimes.

Canada thistle is often a problem in savanna areas. Because it is a perennial, and is also clonal, control requires use of herbicide, but mowing can also help. Many weed manuals recommend mowing at the time of early flower bud stage. The idea is that at this time, most of the root resources have moved to the stems as part of the flowering process, so mowing at that time will starve the roots. However, mowing does not eradicate the clone, but merely sets it back. If mowing is not followed up with herbicide, the clone will thrive and be back in full in another year or two. Here is the ideal approach for Canada thistle: mow as early in the spring as the plants are high enough to mow. Monitor the mowed clone and as soon as new growth has taken place and the plants are in the full rosette stage, spray with clopyralid (Transline or Stinger) or another herbicide specifically recommended for Canada thistle. This herbicide does not affect grasses, which should be seeded into the former thistle clone in order to provide competition for any future development. Control of Canada thistle is a multi-year task, as dormant buds in the clone will form new growth in future years.

Bull thistle may be found scattered throughout a newly restored savanna. It is a biennial and can be readily controlled by digging. As with all biennials, it must be controlled before any danger of seed set.

Reed canary grass is primarily a problem in wetland areas, but does form small infestations in upland sites such as savannas. Reed canary grass is easy to detect at flowering stage, which is the ideal time for control. Patches can be sprayed with a grass-specific herbicide such as sethoxydim (Vantage). Another approach is to tie together the flowering stems of the whole patch, cut the stems above the tie, and squirt concentrated glyphosate (50% or full strength Roundup) down the stems. In the late fall of the year, when reed canary grass is still green but all native vegetation has senesced, patches can be foliar-sprayed with 5-7% Roundup. Because reed canary grass is clonal had has numerous dormant buds, a single treatment will not eradicate. Mark patches that have been treated and return in subsequent years.

Giant mullein is primarily a problem during the early stages of savanna restoration when there are many bare areas, such as burn scars or areas that had been shaded before trees or shrubs were removed. It is a pioneer in such bare areas, but as soon as native vegetation fills in, it is unable to compete. However, it should be removed because its large leaves sprawl out over the ground and prevent “good” plants from getting established. It can be dug with a shovel or cut with a knife. If a lot of mullein plants are in the savanna, a more efficient approach is to spray them with oil-soluble triclopyr ester (Garlon 4). A brief “spritz” of herbicide in the center of the plant is all that it takes to kill it.

Herbicides

Discussion of the use of herbicides has been given above. The purpose of this section is to present a systematic summary of herbicide use in savanna restoration.

Several herbicides are well suited for use in weed and brush control in oak savannas. The herbicides discussed here have been carefully established to be safe and effective if used properly. Before using any herbicide, it is essential that the label be read completely and its specifications followed.

Herbicides are used to facilitate restoration in prairie and savanna ecosystems in conjunction with other methods, including hand pulling, mowing, cutting, prescribed burning, seeding, and cultivation. Herbicides should be used as part of an integrated weed management strategy. The precise treatment method used will depend upon the target species, its life history, the extent of the problem, and the compatibility of the herbicide with the restoration objectives.

The discussion here deals only with non-aquatic habitats. Some herbicides are approved for use in aquatic habitats, but the kinds, uses, and requirements are different.

Spot spraying and broadcast spraying

For most herbicide applications in oak savannas, spot spraying is preferred. This permits application of the chemical just to the target species. Foliar application should be made with a low-pressure (20-50 psi) backpack sprayer equipped with a wand applicator. A sprayer nozzle which creates a flat or cone-shaped pattern is preferable. The herbicide should be allowed to dry for at least two hours to ensure adequate absorption. (Do not spray when rainfall is threatened.) Addition of a nonionic surfactant to the mixture helps ensure complete leaf coverage and increases the rate of absorption. The herbicide should thoroughly cover the foliage but not to the point of run-off. Personnel applying herbicide must be properly trained and knowledgeable about the native vegetation.

Broadcast spraying is used primarily when a site is to be completely killed because there is nothing “good” there. In oak savanna restoration, this approach would be used when planting understory vegetation on a former pasture with large open-grown oaks. Since the pasture grasses are almost certainly exotic cool season grasses, they must be eliminated. It must be ascertained first that all of the existing vegetation is undesirable. The field can then be treated with a nonspecific herbicide such as glyphosate, which kills all existing vegetation. Since the scattered oaks make it impossible to spray with a boom sprayer, an alternate procedure must be used.

A small utility vehicle capable of holding a 100 gallon tank of herbicide and a long hose can be used. The hose is connected to an electrical pump with a hand-held spray nozzle. The electrical pump is controlled by a pressure valve. An operator on foot operates the nozzle. (With the proper pump and controller it is possible for more than one operator to work at the same time.) The site is marked into swaths and the operator moves across the unit, directing the spray nozzle at the vegetation and ensuring complete coverage. Although time consuming, this approach is very effective in eliminating all cool season exotic grasses.

The herbicide label

Detailed information on each of the above herbicides can be obtained from its label. The term “label” here is a misnomer, because the label is generally a multi-page booklet. The complete label for the herbicides listed above can be obtained from the manufacturer’s web site, usually as a PDF file. For all these herbicides, the label should be read and followed!

It should be emphasized that herbicide use should be part of a total management system. As the table shows, none of these herbicides is completely specific. Care must be taken to ensure that sensitive non-target species are not treated.

Outline of procedures for herbicide use
• Herbicide label directions must be carefully followed.

• Protective gear should be worn as per the label directions.

• Herbicides must be labeled and stored appropriately, and used containers must be disposed of properly.

• Empty containers should be rinsed at least three times with clean water and the rinse water must be disposed of per Environmental Protection Agency (EPA) guidelines.

• If an herbicide is used in a public area, notices must be posted near all treated areas.

• Livestock should not be permitted in treated areas until the herbicide has dissipated.

• Wind speeds must be less than 10 mph to minimize herbicide drift.

• Areas to be treated should be surveyed first to ensure protection of non-target species. Only spot applications should be used in areas containing sensitive plant species.

• Personnel who function as commercial herbicide contractors must be certified.

Examples of herbicide use for invasive plants

• 2,4-D. This herbicide is widely used for weed control in lawns and other urban settings. It is active against broadleaf plants (dicots) only; grasses are unaffected. In natural areas., 2,4-D can be used for spot spraying broadleaf weeds such as wild parnsip. However, if there are desirable broadleaf species nearby, hand pulling is preferable.

• Glyphosate is a broad-spectrum herbicide and kills virtually all plants. Within a few days after spraying the plants start to wilt and brown up. Widely used for cut stem treatment of woody shrubs (but see Section on Woody Shrubs above). The chemical moves to the roots and kills the root system.

• At approved concentrations, sethoxydim is active only against grasses; neither sedges nor broadleaf plants are affected. It has been found effective in the control of reed canary grass.

• Triclopyr is widely used for the control of woody vegetation. Like glyphosate, it can be used to treat cut stems to prevent resprouting. One chemical form, Garlon 4, is soluble in oil and can be used to control woody vegetation by basal bark treatment (see above).

• Clopyralid is unusually effective against plants of the legume and sunflower families. It is used for the control of legumes such as crown vetch and black locust, and of composites such as Canada thistle and spotted knapweed.

• Fosamine is used for control of woody plants such as brush and brambles in noncropland areas. It is applied as a foliage treatment during the growing season. Treated woody plants remain green for the remainder of the growing season but fail to leaf out the next spring. Only the foliage sprayed will be affected, and other parts of the plant will remain alive.

• Imazapic will control most broadleaf weeds as well as cool-season grasses such as smooth brome and quack grass.

Properly used, herbicides have wide utility in elimination of invasive plants and the restoration of natural areas. For specific recommendations, consult the herbicide label or use the manufacturers advice.