Control of Invasive Plants in Oak Savannas

Control of invasive species, both woody and herbaceous, generally becomes a major part of any oak savanna restoration project. The principles and techniques presented here are applicable to both the initial restoration work and the long-term management of the savanna. In many situations, the original restoration work moves quickly into long-term management.

Shrubs

Although there are some differences across the Midwest states in the invasive shrubs that cause the most problems, the principles of control for all these species are similar. Often site to site variation within a state may be greater than state to state variation.

Shrubs differ from trees. They are shorter (usually under 15 feet tall), have multiple stems, and have shorter life spans. Some trees grow occasionally as shrubs, generally when young. Also, a few species of shrubs can develop into trees, especially under protected conditions.

Shrubs are widely used in residential and commercial landscaping, and there has been a tendency to use certain nonnative species because they are more successful under the generally harsh conditions that often prevail. Unfortunately, some of these nonnative species have “escaped” into natural areas, where they present considerable problems.

Out of ignorance, some nonnative shrubs have even been highly recommended by government agencies to landowners and commercial growers. Buckthorn, honeysuckle, multiflora rose, and autumn olive have in the past been widely planted. Buckthorn is still used commercially, although efforts are now underway in some states to make its use illegal. The tendency now is to substitute suitable native shrubs.

Problem shrubs of the Midwest
Latin name Common name
Nonnative species  
Berberis thunbergii Japanese barberry
Celastrus orbiculatus Oriental bittersweet
Elaeagnus angustifolia Russian olive
Elaeagnus umbellate Autumn olive
Lonicera maackii Amur honeysuckle
Lonicera morrowii Morrow honeysuckle
Lonicera tatarica Tartarian honeysuckle
Lonicera x bella Bells honeysuckle
Rhamnus cathartica Common buckthorn
Rhamnus frangula Glossy buckthorn
Rosa multiflora Multiflora rose
Native species that may be invasive  
Cornus racemosa Gray dogwood
Cornus stolonifera Red osier dogwood
Rhus glabra Smooth sumac
Rhus typhina Staghorn sumac
Rubus sp. Blackberries, raspberries, and dewberries
Xanthoxylum americanum Prickly ash
 

How shrubs grow

A characteristic growth pattern of all shrubs is the ability to resprout if the main trunk is cut. Shrubs (like plants in general) exhibit a phenomenon called apical dominance, arising because the main growing bud of the shrub produces a growth hormone that is transported to the roots and inhibits the growth of dormant buds. When the hormone source is eliminated by cutting, growth of a few or many of these dormant buds is initiated, resulting in the production of multiple shoots. Eventually, over a few more years growth, one or two of these new shoots may become dominant and produce enough hormone so that buds at the base go dormant again.

Pruning a shrub to control its shape and form makes use of the apical dominance phenomenon. Top-killing a stem by fire also eliminates apical dominance.

Whether apical dominance is eliminated either by cutting, girdling, or fire, the end result is the same: multiple shoots develop. It is not possible to eradicate a shrub simply by cutting it, and fire also does not eradicate.

Clonal growth of shrubs

Certain species of shrubs spread by means of horizontal stems called rhizomes which grow underground for some distance from the original plant before forming new above-ground shoots. Species in the above table that are clonal are buckthorn, gray dogwood, red-osier dogwood, sumac, Rubus species, and prickly ash. To eradicate these species the whole clone must be eliminated.

Clonal growth of prickly ash (Xanthoxylum americanum). Although this is a native species and good bird habitat, only a few clones should be retained in any savanna restoration.

Herbicides and shrubs

The goal of herbicide treatment is the complete killing of the shrub, and many herbicides are effective for this action. Herbicide applied to the cut stems of a shrub is transported to the roots where it accumulates in the roots, root collar, or basal stem. The herbicide either kills or inhibits the growth of the shrub. However, if insufficient concentration of herbicide is applied, the living shrub tissue may “escape” treatment and begin to grow again in a following season. This is one reason why a single herbicide treatment may not be sufficient to eradicate a shrub.

Despite reports to the contrary, cut stems of shrubs can be treated with herbicide in the winter.

Control strategies for shrubs

Techniques for eradication of invasive shrubs make use of the principles of shrub growth just discussed. In most cases herbicide will be needed as part of an integrated management system.

Cut and treat. All the stems are cut (by chain saw, motorized brush cutter, or hand loppers), and every cut stem is treated with a suitable herbicide.

Basal bark. The bases of the stems are sprayed with an oil-soluble herbicide dissolved in a penetrating diluent such as diesel oil, kerosene, or bark oil. The oil penetrates the bark and carries the herbicide to the stem where it is transported to the roots.

Foliar spray. The shrub is sprayed with an aqueous solution of an herbicide. The herbicide is taken in through the leaves and transported throughout the plant, resulting in death of the plant.

Girdle herbicide application. If girdling is to be used, an herbicide is applied to the cuts. Either a water soluble or an oil soluble herbicide can be used. Girdling alone will not eradicate shrubs. All it does is eliminate apical dominance, resulting in growth of dormant buds. Where a single stem might have been present before girdling, several to many new shoots will arise.

• Hand pulling most likely will not eradicate shrubs. Hand pulling is often recommended by those trying to avoid the use of herbicides. Certain species can be eradicated by this method, but many shrubs have impressive root systems, parts of which are left below ground when the shrub is pulled and grow and restablish the infestation.

Basal bark treatment

For the initial stages of an oak savanna restoration, or for a major infestation, the most economical method is the use of basal bark treatment. This should be effective for all of the shrubs listed in the table above, although some may be more difficult to treat than others due to their physical structure.

Basal bark treatment is recommended for woody plants less than six inches in diameter, which would include almost all shrubs.

An herbicide which has been widely used for basal bark application is triclopyr, in the form of its butoxy ethyl ester (trade name Garlon 4; 61.6%, 48% triclopyr acid equivalent ). Garlon 4 should be used at a 20-30% solution (20 ounces or 30 ounces of herbicide in 100 ounces total product). It can be mixed with mineral oil, “bark oil”, or “Diluent blue” (available commercially from agricultural chemicals supply companies). The commercial diluent contains a dye which aids in proper application. If a diluent such as mineral oil is used, a red or blue dye obtained from an agricultural supply company can be used.

The basal bark procedure involves spraying a 10-15 inch band of herbicide at the base of each stem. Spray to thoroughly wet the whole area, but not to the point of runoff. A nozzle with a flat fan spray pattern is ideal and a low-pressure sprayer is recommended. To prevent spray moving past the target, keep the nozzle close to the stem being sprayed. Application can be done at any time of the year, including winter, except when the stems are wet or have snow on them. This procedure works because the bark is lipophilic, and the oil diluent readily wets the bark and allows oil-soluble substances such as the herbicide to penetrate.

Although it is recommended to spray completely around the stem, for small stems (less than one inch in diameter), one-sided spraying can be done, applying a 10-15 inch band of herbicide.

Basal bark treatment has a number of advantages:

• Effective year around (although not recommended when the air temperature is above 70 F).

• Highly selective, since only the plant sprayed receives the herbicide.

• Herbicide can be applied from a backpack sprayer, making it possible to move quickly through the area.

• Herbicide is confined just to the plant, reducing any effect on surrounding native species.

• If used during the dormant season, the treated shrub does not leaf out the following spring. Thus, there are no brown leaves. This has an advantage in public areas.

• No cutting is needed. The roots of the dead shrubs will eventually rot and the shrub will fall over. Since the leaves are eliminated right away, increased light to the forest floor occurs, encouraging growth of native species. Overseeding of native species should be done in areas where large infestations have been treated.

Backpack sprayers are best for basal bark application of herbicide. Snow-free periods during the winter are excellent times for this work. Here a sumac clone is being treated. This clone had been marked in the fall from its characteristic red leaves, so that it could be attacked when time permitted.


Cut stem treatment

A general method suitable for all shrubs is to cut them with a saw, loppers, or hand clippers and spray the cut stems with herbicide. This works very well for small-diameter shrubs or large clones where basal bark treatment is difficult. For large infestations, a powered brush cutter or chain saw should be used.

Either Garlon 3A in water or Garlon 4 in oil can be used to treat the cut stems. The latter has the advantage that occasional stems that missed the cutter can be basal barked.

For small shrubs or minor infestations, the cut stems can simply be left on the ground where they will burn up during the next prescribed burn. If a large shrub infestation is being dealt with, the cut stems should be piled so that they can be burned later. Once the stems have dried for a few months, they will be flammable and can be ignited easily. See link for brush piles procedures.

Note that cutting without herbicide treatment should not be done. It is ineffective, and there will be extensive resprouts from the cut stem the next growing season.

Several herbicides are suitable for cut stem treatment although not all of them are equally effective. The table below has some suggestions.

Cut stem work can be done either with hand-held loppers or a motorized brush cutter. A dye should be added to the herbicide mixture to ensure that treatment is complete.

 

Herbicide recommendations for cut stem treatment
Shrub Herbicide
Japanese barberry Glyphosate
Amur honeysuckle Glyphosate
Morrow honeysuckle Glyphosate
Tartarian honeysuckle Glyphosate
Bells honeysuckle Glyphosate
Common buckthorn Triclopyr (Garlon 3A or 4)
Glossy buckthorn Triclopyr (Garlon 3A or 4)
Multiflora rose Triclopyr (Garlon 3A or 4)
Gray dogwood Glyphosate
Red osier dogwood Glyphosate
Smooth sumac Garlon 4 as basal bark, either with or without previous cutting
Staghorn sumac Garlon 4 as basal bark, either with or without previous cutting
Blackberries, raspberries, and dewberries Triclopyr (Garlon 3A or 4)
Prickly ash Triclopyr (Garlon 3A or 4)
Herbicides should be used at 20-30% active ingredient (the label will indicate the concentration of active ingredient in the product itself). See also this link

Glyphosate has the advantage that it has no residual activity in the soil, as it is inactivated by soil particles. However, glyphosate is less effective against buckthorn, multiflora rose, or sumac. Sumac has an additional problem. It has a milky sap which prevents water-soluble herbicides from moving down the cut stem. The best procedure with sumac is to use Garlon 4 in oil as a basal bark, either with or without cut stem treatment.

Foliar spray

For smaller infestations foliar spraying with glyphosate or triclopyr can be done. If the shrubs are scattered and surrounded by good species, then selective spraying of the leaves with a backpack sprayer should be done. In an area where there are no “good” species, broadcast spraying with high-volume equipment can be very economical. The herbicide concentration used for foliar spraying is much lower than that used for basal bark or cut stem treatment. The herbicide label will specify the concentration to use. In general, the concentration is between 2 and 4% "out of the bottle"..

If foliar spraying is desirable but the infestation consists of large-sized plants which cannot be sprayed without contaminating the environment, an alternate approach is possible. Cut the shrubs with a brush cutter or chain saw and remove the cut material from the site but do not treat the cut stems. Allow the resprouts to grow until they are about six inches tall and then use a foliar spray. The initial cut should best be done in mid summer, so that the resprouts can be sprayed at the end of the summer while they are still growing.

Management of a shrub removal activity

The overall management of shrub removal, especially in the initial stages of oak savanna restoration, should be organized systematically. If basal bark treatment is being used, the area to be covered should be divided into swaths of 15-20 feet wide, marked with flagging, using a compass to keep a straight line. The worker or workers then walk back and forth along this swath and basal bark every undesirable shrub. Once the swath is completed, return via the next swath. Move back and forth until the whole unit has been dealt with.

If tree removal is also being done, then the two activities can be done at the same time. If the trees being removed are being burned at the site, then the cut shrubs should be burned at the same time the tree slash is burned. Since the cut shrubs are small, they can be easily ignited and can serve as the base for the burn pile.

Eradicating buckthorn (Rhamnus cathartica)

Buckthorn (Rhamnus cathartica) is one of the more annoying invasive plants to deal with. Introduced in the 19th century, it has become well established over eastern North America. Even though its evils are now well recognized, it is still sometimes used commercially as a hedge or ornamental.

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.
 

In many natural areas buckthorn is the predominant understory shrub in woodlands and savannas, and it is also common on roadsides. The buckthorn plant may grow as a many-stemmed bush up to 10-15 feet high, and when older can often take the form of a small tree up to 30 feet high. Many specimens in well established stands can be over 50 years old. Although the species is dioecious, the ratio of female to male plants can be as high as 6:1, making it a prolific berry producer. A very high seed bank (620 seeds/ m2 ) was reported in Canadian work.

Buckthorn plants produce a chemical (toxin) which is active in soil. A major buckthorn infestation may result in a "buckthorn desert". After eradicating the buckthorn plants, it may take a few years for the toxin to dissipate. This chemical activity may explain why dense monospecific stands of buckthorn often occur.

According to work in England, where it is native, common buckthorn is a strong calciphile, and is found chiefly on alkaline peat and limestone soils. This may explain its absence from many sandier areas.

If an oak savanna area has a lot of buckthorn, special attention should be placed on its eradication. Although the original (“old-growth”) buckthorns are readily eliminated by cut stem or basal-bark herbicide treatment, the huge seed bank makes total eradication much more difficult.

The first growing season after the buckthorns have been removed there may be a large number of small seedlings derived from the heavy seed bank. If allowed to persist, within a few years there will be small patches and major infestations visible. The buckthorn plant forms a very extensive root system, and dormant root masses may persist for years in a formerly infested site. The root system of buckthorn is a massive fibrous tangle of small and large roots.

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.
Of course, basal bark can be done any time of the year, even winter, although it takes more skill in the winter to find the naked buckthorn stems.

• Do foliar spraying with triclopyr in the fall after the native vegetation has senesced. Buckthorn retains its foliage in the fall for weeks after the native vegetation has died back. This makes it possible to use a foliar spray selectively. However, the timing of foliar spraying is tricky, since as soon as the stems start losing leaves, foliar spray starts to become less effective.

• Hand-cut and herbicide-treat small buckthorns in the winter. Although laborious, this procedure should be the most benign as far as the native vegetation is concerned. The herbicide should be triclopyr (15-20% in oil) used as a basal bark. Do not treat only the cut stems, but also spray the stem below the cut down to the root collar (basal bark treatment), using a hand spray bottle. Avoid getting any herbicide on the soil itself, as triclopyr has a soil residual and will prevent native forbs from becoming established.

• Burn in the spring in areas where buckthorn plants have already been removed. Spring burning is the best because it will come after the fall/winter control work, so that there should be no remaining buckthorn stems to be top-killed. Burning will also encourage the growth of native species, and their competition will hopefully help to suppress new buckthorn growth. Burns will also top-kill and buckthorn plants that have been missed. The new shoots from these top-killed plants will be visible within a month and can be sprayed with foliar triclopyr (Garlon 3A) (glyphosate also works as a foliar spray at this time of year).

• Reseed with native species, especially in areas where large buckthorn infestations have been eradicated. For areas where triclopyr has been used, reseed predominantly with native grasses, since they are not affected by the herbicide. Although these areas may well start out as “buckthorn deserts” due to the residual effect of the buckthorn toxin, they should be planted anyway, since some of the newly planted species will become established. Unfortunately, there is no research on whether any native species are resistant to the toxin. Experience has shown that native species begin to dominate about the third year after buckthorn removal.

• Continue monitoring for new infestations, and deal with them by the above methods.

How long will the seed bank last? Unfortunately, there are no data on this, although small buckthorn plants have been found in restored oak savanna areas in Wisconsin as long as 10 years after initial eradication. These have probably arisen from dormant root masses.

 

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.

Bush honeysuckles are upright shrubs ranging from a few feet to 15 feet tall. They form many branches from the base, and the spreading branches shade other plants. In a honeysuckle "thicket", almost nothing will be found under the canopy. (After the honeysuckle is removed, the soil is often bare.) Honeysuckles form fragrant tubular flowers, followed later by red fruits. Birds are attracted to the fruits and spread the seeds. Bush honeysuckles have a wide environmental tolerance, but they prefer partial to full sunlight and are most commonly found in abandoned fields, forest edges, roadsides, and other open upland habitats. They are extremely invasive and can easily take over and dominate a habitat.

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

Bush honeysuckle is one of the plants that will invade a habitat if it is protected from fire. Once honeysuckles have conquered a habitat, there is no possibility of fire because there is no fuel. In order to reintroduce fire, it is essential first to eliminate the honeysuckles and then reseed with native plants, preferably seed mixtures containing grasses that will carry a fire.

Both mechanical and chemical methods are used on honeysuckle, and often both together. The most assured method is to cut all the stems of a plant and treat each cut stump with a 20% solution (active ingredient) of glyphosate.

Honeysuckle can be cut with a chain saw, brush cutter, or hand lopper. For an occasional plant, a hand lopper is fine, but for any extensive honeysuckle thicket, a motorized cutter is essential.

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.
 

With a group of volunteers, an ideal way to work is with one person operating a brush cutter or chain saw and several persons making brush piles and treating the cut stems with herbicide. (A skilled brushcutter can cut enough to keep three or four volunteers busy treating.)

However, a single person can also make significant inroads into a honeysuckle thicket. Here is a procedure guaranteed to work: Cut each stem with a hand lopper or handsaw, counting the stems as you cut. Cut the stems as close to the ground as possible, but still leave a small amount of stem showing above the soil layer. Pull all cut stems away from the base. Now treat each cut stump carefully with the glyphosate mixture.As you treat, count each stump again, and do not stop treating until you have treated every stump you have cut. If a spray bottle is used, do not spray the whole base, since this wastes herbicide and spreads it around. Instead, place the tip of the spray bottle onto each cut stump, press gently to bring up several drops of solution, and spread them around the cut stump with the tip of the bottle. The whole cut stump should be colored with the dye/herbicide mixture (see photo). With practice, this procedure works quite well and the honeysuckle plants should not resprout.

Honeysuckle can be cut and treated at any time of the year, although the winter is often preferable because of the lack of foliage. Glyphosate does work in winter!

Small honeysuckle plants can also be killed by foliar spraying with a 2-4% solution of glyphosate (active ingredient). It is important that all leaves be sprayed. Honeysuckle is so sensitive to glyphosate that the plant should be killed within a few weeks. More importantly, the root system is also killed, and within a year the dead shrub can be readily pulled up.

Honeysuckle is very persistent, and will resprout readily if not treated with herbicide.

After the honeysuckles have been taken care of, the area should be reseeded with native species. This is especially important because when the honeysuckles were removed a "hole" has been created, into which weeds will readily move.

Once large honeysuckles have been eliminated from a natural habitat, the work is not finished. There will be a seed bank, so that small honeysuckles will appear next year. Fire will top-kill these new plants but will not eliminate them. After a few years, there will be numerous knee-high plants scattered throughout the savanna. Although these can also be cut and treated, a more efficient way of dealing with the honeysuckle resprouts is by foliar spray in the fall of the year, after the native vegetation has senesced. The honeysuckle leaves remain green and viable and can be easily seen sprayed at that time. Glyphosate works well, and because the native vegetation has all senesced it will not be affected. Add a blue dye to the herbicide in order to be able to follow the foliar spray.

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.
Brambles (Rubus sp.)

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 photo below shows the arrangement of canes, shoots, and roots at the base of the plant. There are several dormant shoots. Iif the above-ground shoots are killed by fire or cutting, one or more of the dormant buds will begin to grow and form a new canes.

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.

Some brambles (black raspberry, northern dewberry) exhibit a phenomenon called "tip-rooting." Canes whose tips reach the soil can form new roots, enabling the brambles to colonize new bare areas. Bramble patches with tip-rooted canes are especially difficult to walk through.

Since flowers only develop on the second year shoots, annual fire will keep brambles from flowering and setting seed, but will not eradicate them. In the next growing season, each killed cane will develop a rosette of leaves from an underground bud. By mid-summer, a new vigorously growing cane has been established.

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.

Control of brambles in savanna restoration Although they are all very fire-sensitive, they are not eradicated by burns, since the roots remain alive and resprout. Eradication of brambles in savanna restoration can only be done with the use of herbicide. Even then, removal requires careful monitoring and consistent control.

The surest way of removing brambles is by cutting the canes and treating the cut stems with glyphosate (20% active ingredient). Brambles are easily cut with hand clippers, and a single person can cut and treat an area, with clippers in one hand and herbicide bottle in the other. It is essential that every cane be cut and treated. Some of the canes may be dead. These do not need to be treated, although it is still desirable to cut them. Living cut stems are easily recognized because they will be green and moist, even in the winter. Eradication by the cut-and-treat method is very time-consuming, but is the surest way. Once the brambles have been removed, annual burns should be carried out for a number of years, since there will always be a seed bank, and in the absence of fire the area would eventually return to an unrestored state.

In areas with large bramble patches, especially those where there are no "good" plants, foliar spraying can be done. Roundup (glyphosate; 1-1.5% foliar spray) is labeled for blackberry and should work on other members of the genus Rubus. According to the manufacture, best results are obtained when plants have reached full leaf maturity in late summer or fall. Garlon (triclopyr; 0.5-1% foliar spray) and Krenite (fosamine; 5-10% foliar spray) are also labeled by their manufacturers for blackberry and would presumably work for the others. However, all of these herbicides have the potential for harming nontarget plants and should only be used in areas where there are no desirable plants. (Some reports state that Krenite only affects woody plants, but this is not true. Krenite also affects many grasses and forbs.)

One additional procedure that may aid in bramble control is to cut the plants in mid-summer, at flowering time. At this time of year, most of the nutrients are in the stems, and if these are severed the roots will be starved. We have found this procedure to be helpful, although it does not completely eliminate the brambles. One advantage of cutting at flowering time is that berries will not yet have been made, thus eliminating the chance of adding to the seed bank.

If fire cannot be used, and desirable nontarget species must be protected, complete elimination of brambles from an area is still possible using the cut-stem procedure described. Although laborious, this procedure is quite effective. It is best done in the winter, because herbaceous vegetation will be dormant, thus eliminating any side damage from the use of herbicide.

In most cases, brambles will be a minor component of the woody vegetation, with honeysuckle, buckthorn, and other woody plants dominating. Since all of these species can be eliminated by herbicide treatment of cut stems, brambles can be removed along with the others.

Rubus always has an extensive seed bank, so that effective bramble control requires frequent, preferably annual, burning as well as reseeding with herbaceous savanna species, since competition from other plants is an important factor in keeping brambles from becoming reestablished. Because fire will not eliminate the seed bank, it is also essential to return to previously restored areas periodically and repeat the cut-and-treat method.

The table below summarizes the characteristics of the principle species of brambles likely to be found in oak savanna restoration.

Latin name

Common name

Growth form

Control methods

R. allegheniensis

Black raspberry

Large canes; do not tip root

Cut and treat with glyphosate or triclopyr

R. flagellaris

Dewberry

Vine-like; trailing along the ground; tip root

Foliar spray with triclopyr of new growths after burns

R. idaeus

Red raspberry

Dense clones; do not tip root

Foliar spray with triclopyr of new growths after burns

R. occidentalis

Black raspberry

Long arching canes that tip root

Cut and treat with glyphosate sometimes; triclopyr recommended; foliar spray with triclopyr of new growths after burns

 


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.

Invasive herbaceous weeds of possible concern in savanna restoration
Latin name Common name Growth Severity[1] Control methods
Alliaria petiolata Garlic mustard Biennial High Spring and fall spray; hand pull
Arctium minus Common burdock Biennial Low Spring spray
Centaurea maculosa Spotted knapweed Perennial Low Spring and fall spray
Cirsium arvense Canada thistle Perennial Moderate Spring spray; summer mow; fall spray
Cirsium vulgare Bull thistle Biennial Low Hand pull or dig
Coronilla varia Crown vetch Perennial Low Spring and fall spray
Daucus carota Queen Annes lace Biennial Low Hand pull or mow
Dipsacus laciniatus Cut-leaved teasel Biennial Low Hand pull or mow
Dipsacus sylvestris Common teasel Biennial Low Hand pull or mow
Euphorbia esula Leafy spurge Perennial Low Hand pull or mow
Hesperis matronalis Dames rocket Biennial Low Hand pull or mow
Leonurus cardiaca Motherwort Perennial Low Hand pull or mow
Lotus corniculatus Birds-foot trefoil Perennial Moderate Hand pull or mow
Lythrum salicaria Purple loosestrife Perennial Low Spray when found
Melilotus alba White sweet clover Biennial High Hand pull or mow
Melilotus officinalis Yellow sweet clover Biennial High Hand pull or mow
Pastinaca sativa Wild parsnip Biennial High Hand pull or mow
Phalaris arundinacea Reed canary grass Perennial Low Spring and fall spray;summer cut followed by spray of cut stems
Torilis japonica Japanese hedge parsley Biennial or winter annual Moderate Hand pull or mow
Trifolium repens White clover Perennial Low Spring spray
Verbascum thapsus Mullein Biennial Moderate Hand dig or pull; late fall spray with triclopyr or glyphosate
 
[1] Severity refers to savannas only. Many of those listed with low severity are extremely bad in prairie or wetland habitats.    


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.

Summary of characteristics of some selected herbicides
Herbicide Trade names Target species Unaffected species Environmental characteristics
2,4-D Generic Broadleaf herbaceous plants Most monocots, including grasses Half-life in soil 7-10 days; safe for aquatic uses
Glyphosate Generic Nonselective; grasses, forbs, vines, trees, shrubs None No residual; iinactivated by soil particles
Sethoxydim Vantage Grasses Broadleaf herbs, sedges, woody plants Half-life in soil 4-5 days
Triclopyr Garlon 3A and 4 Broadleaf herbs and woody plants Most monocots, including grasses Half-life in soil 30 days
Clopyralid Transline Broadleaf weeds Grasses Half-life in soil 40 days
Fosamine Krenite Woody plants Herbaceous plants less affected Rapid degradation and high binding to soil particles
Imazapic Plateau Grasses; some broadleaf species Many broadleaf species Half-life in soil several months
 

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.

 

Burning Brush Piles

Brush piles are often created during the management of prairie and savanna restorations. Such brush piles frequently present problems during prescribed burns if they have not been properly located. The intense heat from a burning brush pile can kill or cause serious damage to nearby trees. A burning brush pile can often cause spot fires well outside the burn unit.

Brush piles that have been on the ground for some period of time are extremely flammable and during prescribed burns may get ignited by flying embers even when they are well outside burn units.

Rotten logs and stumps which are rather porous are often prone to ignition via glowing embers (spot fires), even though leaves and sound wood are resistant. Why is this so? Sound wood conducts heat so effectively that the heat from a burning ember spreads out quickly, effectively putting the fire out. On the other hand, porous fuels such as punky wood conduct heat poorly, so that the heat of an ember remains on the surface where it can cause ignition. Although they do not flame, these porous fuels can achieve glowing ignition from a relatively modest input of heat. Once ignited they can smolder for weeks, with the possibility of being fanned into flames by dry winds.

How are brush piles created? Many undesirable trees are cut during savanna restoration, producing lots of wood. Downed trees are occasionally arise as a result of windthrow. Brush piles are also created in many tree removal operations. Removal of invasive woody shrubs produces much wood, which is most easily disposed of by burning in a brush pile.

How to avoid problems? Try not to create brush piles in the first place. If conditions are suitable, burn the wood as it is being cut. Start a fire with a small amount of downed dry wood, and feed this fire as cutting proceeds. Ideally, this approach should only be used when snow is present. In the absence of snow, clear a wide stick- and leaf-free zone around the pile to ensure that the fire does not spread. In some areas and at certain times of year, depending on the governmental unit, a permit may be needed to burn a brush pile.

Build brush piles well away from any living trees. A large pile should be at least 10 feet (preferably farther) from any desirable trees. Look up to be sure that limbs are not hanging over any part of the pile.

In addition to living trees, brush piles should be constructed well away from dead trees. Although standing dead trees are great bird habitat, they are serious hazards in prescribed burns. To keep them from igniting, brush piles that may burn should be placed far away.

Build as few brush piles as possible. A few large piles are easier to manage than many small piles. However, to avoid high flame lengths, brush piles should be no more than 10 feet high. Build brush piles into compact structures. Loosely constructed piles are difficult to ignite.

If a brush pile is inside the burn unit, it should be at least 20 feet from any fire breaks. The taller the pile, the farther it should be built from the fire break.

A newly created brush pile will not burn well. Wait at least six months before burning it. If it must be burned right away, then do not make a brush pile but burn the wood as it is being cut, using drip-torch fuel to ignite the pile.

As soon as snow is present, burn all remaining piles. Do not delay, as snow cover may not last.
Igniting brush piles. If the pile is very dry, ignition is easy. For piles of freshly cut material, liquid fuel is needed. Drip torch fuel (2 parts diesel, 1 part regular gasoline) works well and is relatively safe, although there is a slight danger of flashback. An alternative is diesel alone, with a butane torch to ignite the diesel. Instead of a butane torch, a propane torch such as is used for killing weeds can be used. This has a long wand, so that the operator is well away from the igniting pile.

It is preferable to burn brush piles early in the winter than to wait for possible snow (which may not come). The best time to burn is on a day with a light misting rain. (Use liquid fuel to aid in igniting.) Another way to burn in the rain is to keep the pile dry by covering it with a waterproof cover. Remove the cover at the time of ignition. Burning in very dry weather should be avoided. Adequate personnel must be available to monitor piles. Clear a leaf- and stick-free zone around each pile to ensure that fire “creep” does not occur. Have a water can available just in case.

Ideally, there should be no brush piles remaining inside burn units at the time of ignition.
If piles are still present at the time of ignition, two possibilities exist. They can either be allowed to burn as part of the fire, or they can be protected from burning. Provided they have been properly constructed (away from living trees, well inside burn units, etc.) it is preferable to let them burn. However, a large burning brush pile is a potential hazard, since it produces intense heat and sparks that may fly well outside the burn unit, causing spot fires.

Protecting a large dry brush pile from burning when it is inside the burn unit is difficult, sometimes impossible, especially when it is very dry. Two things must be done: All fuel within a six feet radius of the brush pile should be removed. During the burning process itself, a black line must be created around the brush pile. To create such a black line, an adequate supply of water is essential to keep the fire contained.

In summary:
• Create a limited number of well-constructed brush piles
• Construct them well inside burn units.
• Construct them well away from trees.
• If possible, burn all brush piles separately from the prescribed burn.
• Protect living trees from burning brush piles

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