Control woody vines in landscapes
Management of weeds is a significant component of landscape-maintenance programs. One important weed group is the woody vines, which pose special problems in our landscapes:
*Vines climb desirable trees and shrubs, causing uneven growth by blocking sunlight
* Excessive vine growth can break tree branches due to excessive weight
* Vines growing on trees for extended periods can cause girdling
* Poison ivy can cause severe allergic reactions in most people
* Some vines, such as greenbrier and brambles, have sharp spines
* Woody vines grow over fences, obscure highway signs and climb poles, interfering with electrical, telephone and other lines * Woody vines are difficult to control, often requiring repeated chemical applications.
For these reasons, as well as aesthetic considerations, woody vines are important weed problems in ornamental beds, parks, fencerows and along highways. Most viny weeds are broadleaved (dicots). One exception is greenbrier (Smilax spp.), a perennial monocot in the lily family (though it actually has "broad" leaves). Viny weeds can be annual or perennial.
Annuals. Summer-annual weeds with viny growth include ivyleaf morning glory, burcucumber and mile-a-minute weed. These and other summer annuals never become woody and die with the first hard frost. Winter annuals with viny growth include some of the vetches. Winter annuals die off when hot, dry weather arrives in late spring or summer.
Perennials. Perennial vines can and do spread by seed but also can spread vegetatively by rhizomes, stolons, rooting of stems or creeping rootstocks. In general, perennial weeds are more difficult than annuals to control due to their extensive root system and ability to spread vegetatively but also because most pre-emergence herbicides have no effect on established perennial weeds. Certain pre-emergence herbicides do control annual viny weeds. Unfortunately, grounds managers often find that by concentrating on strategies that control annual weeds, such as mulches or pre-emergence herbicides, perennial weeds increase with time. Mowing or cutting the stems doesn't control these weeds because they can regrow from rootstocks.
Perennial weeds may be herbaceous or woody. Herbaceous plants die back to the ground in fall or early winter, and regrow from rootstocks, rhizomes or other underground structures in spring. Examples include field and hedge bindweed. Herbaceous perennials have no persistent woody stem above ground. Woody perennials, conversely, have aboveground stems that survive and grow year to year.
Common woody-vine pests Several woody-vine species occur frequently in landscapes and other non-crop areas. Below are some of the most common types.
Poison ivy. Poison-ivy stems (see photo, below left) can trail along the ground or climb up trees, poles and other structures by clinging with aerial roots. However, poison ivy can also grow as a shrub. Its leaves are trifoliate (see figure, page 60)-you may have heard the phrase "leaflets of three, let it be" as a reminder to avoid these plants. The leaves, which have alternate arrangement turn bright red in fall, and the fruit are greenish to grayish-white berries. Approximately one-half to two-thirds of the human population are sensitive to the toxin in poison ivy, which causes a contact dermatitis. The toxin is present in all parts of the plant at all times of the year, even in overwintering stems. Never burn this plant because the toxin may be present in the smoke and can cause lung damage if you inhale it. Poison ivy spreads by seed, creeping rootstocks and rooting of stems into soil.
* Virginia creeper and wild grape. Virginia creeper grows in the same range and habitat as poison ivy, and people sometimes confuse the two. However, the palmate leaves of Virginia creeper generally have five to seven coarsely toothed leaflets (see photo, page 61). This plant climbs by tendrils and, like poison ivy, its stems will root into soil. Birds spread its seed, and the fruit are blue or black.
Virginia creeper is in the same family as wild grape and, like Virginia creeper, various wild-grape species can be serious weed problems. Grape leaves are simple (no leaflets, just one whole leaf) but are sometimes deeply lobed. Grapes climb by tendrils and often grow rampantly over trees and fences. Both wild grapes and Virginia creeper exhibit alternate leaf arrangement.
* Trumpet creeper. Trumpet-creeper leaves are compound, pinnate and alternate, with seven to eleven toothed leaflets per leaf. It climbs by aerial roots, which can damage siding on buildings to which they attach. Trumpet creeper has showy orange, trumpet-shaped flowers that produce a pod containing winged seed. Hummingbirds are attracted to trumpet creeper. One possible way to manage this weed is to dig it up, plant it in pots and sell it as hummingbird vine (a name nurseries often use for this plant)!
* Honeysuckle. Japanese honeysuckle (see photo, above) has simple, opposite leaves, which distinguishes it from the vines I've described so far. The flowers are yellowish-white and fragrant, and the plant is deciduous to evergreen, depending on the region. You may be able to take advantage of the evergreen characteristic of the plant by applying a foliar-absorbed herbicide in fall when it is still in leaf but after desirable deciduous trees and shrubs have dropped their leaves. Importersintroduced Japanese honeysuckle to the United States from Asia as an ornamental (for which it still is used) but it has escaped cultivation and become a significant weed.
*Bitter nightshade. Bitter nightshade is a semi-woody to herbaceous vine in the same family as the tomato and potato. Its leaves are alternate and either egg-shaped or oval with two lobes near the base. The flowers are purple with a yellow center, resembling tomato flowers, and its green berries turn red when mature. This poisonous plant sometimes grows amid ornamental hedges, among other places.
*Brambles. Brambles (wild blackberry, dewberries and other Rubus species) have alternate, compound leaves with three to seven leaflets, toothed margins and prickles on the stems. The white flowers give rise to red or black berry-like fruit. They can grow as shrubs or trailing vines.
*Kudzu. Kudzu is a perennial vine that mostly is herbaceous but can be semi-woody at times. It has large, alternate trifoliate leaves (see photo, below right). Young stems are hairy. Purple flowers produce pods that contain kidney-shaped seeds. Kudzu was intentionally introduced from Japan for forage and erosion control but has escaped cultivation and become one of the most serious weed problems in the South.
*Greenbrier. Greenbrier has alternate, simple leaves with sharp spines on its stems. The leaves are heart-shaped or round, and the leaf petioles have twining appendages that allow it to climb. Greenish flowers produce bluish-black berries.
Woody-vine control in landscape plantings No selective herbicides exist that allow you to chemically control woody vines growing among broadleaf ornamentals. (All chemical controls discussed here are listed in the table on page 61.) Cultural controls include hand weeding and repeated cultivation. Cutting the stems at the soil line does not control these weeds due to re-growth from rootstocks. Cutting the vine at the soil line and then treating the young re-growth with a systemic herbicide is an option when you cannot easily spray the weed's foliage without contacting foliage of desirable plants.
Spraying a contact herbicide such as diquat or pelargonic acid will affect the foliage but will not eliminate underground portions of the vine. (Repeated application gradually can deplete the root reserves of a perennial if you continually spray the re-growth.) A physical barrier such as black plastic or a landscape fabric suppresses establishment of these weeds from seed. However, mulches are ineffective for controlling perennial vines that already are established. Therefore, chemical control is limited to non-selective post-emergence herbicides such as glyphosate (Monsanto's Roundup Pro) and glufosinate ammonium (AgrEvo's Finale).
Roundup Pro, a systemic herbicide, is the compound of choice for most situations because it translocates to roots of perennial vines. However, you may need to make repeated applications to completely kill a perennial vine with a deep, well-established root system. Finale is a contact herbicide with limite translocation in plants. You can expect regrowth from the rootstock following an application with this product, and you'll probably need repeat treatments for long-term control.
To avoid injury to nearby ornamentals when you spray with Roundup or Finale, use a shielded spray. When using directed sprays, avoid contacting the bark of young trees or species with thin or green bark. Both Roundup and Finale can cause bark injury to such plants. Wiper applications of Roundup are another way to apply this herbicide near sensitive ornamentals. You'll need to use higher concentrations of Roundup with wipers-check the label for specific use directions.
You can apply Finale anytime weeds are actively growing. In general, the optimum time to apply Roundup is in late summer to early fall (this range of times is greater in warmer climates), but before frost. One exception is greenbrier, where spring applications are necessary because its older leaves apparently do not readily absorb the chemical. You also can apply Roundup to cut stems or stumps, or inject it into stems, for controlling individual plants. You should make such treatments to actively growing vines immediately after cutting the stem.
Vine control in non-crop areas * Foliar-absorbed products. You can use a wider variety of herbicides in non-crop and non-turf areas than in landscape beds. For example, in addition to Roundup and Finale, combinations of the post-emergence broadleaf herbicides 2,4-D, triclopyr, 2,4-DP (dichlorprop), MCPP (mecoprop) and dicamba are common choices for perennial vine and brush control in areas such as fencerows, along highways and near turf. You cannot use these products in ornamental beds due to the sensitivity of broadleaf trees and shrubs to these growth-regulator-type chemicals.
Post-emergence applications of 2,4-D alone generally do not provide satisfactory control of most woody vines. Therefore, formulators produce various prepackaged combinations of 2,4-D plus triclopyr, dicamba, 2,4-DP or MCPP. Combination treatments, whether from prepackaged formulations or as tank mixes of individual broadleaf herbicides, should satisfactorily control the common woody broadleaf vines. These chemicals are primarily leaf absorbed, and they are most effective when applied to the foliage of actively growing vines in spring to early summer. Wet all foliage for optimum results. On warm, sunny days the treated vines quickly will show the effects of treatment. You also can apply these combination treatments to cut stumps or bark (applicators often mix them with oil for greater effectiveness).
Applicators sometimes use combinations of Roundup and 2,4-D to control certain perennial vines. However, where nearby sensitive ornamentals restrict the use of the broadleaf herbicides, you can use Roundup alone.
Fosamine-ammonium (DuPont's Krenite) is yet another option. You apply it as a foliar spray in late summer to early fall-thorough coverage of all foliage is important. An advantage of Krenite is that it doesn't cause "brown out." Most herbicides you apply during the summer leave brown, dead foliage after the weed dies, which some people find objectionable. However, sensitive weeds treated with Krenite in the fall simply fail to leaf out in spring, avoiding the "brown out" effect. Imazapyr, American Cyanamid's Arsenal, is another product that is foliar absorbed (in addition to soil activity-see next section) for use in non-crop areas. This non-selective systemic product is commonly used in vegetation-management programs.
Soil-active products. Certain non-crop herbicides have long soil residuals. Chemicals such as imazapyr, sulfometuron-methyl (DuPont's Oust), metsulfuron-methyl (DuPont's Escort) and tebuthiuron (Dow's Spike) control certain woody vines in non-crop areas. Because some of these herbicides can remain active in the soil for 6 to 12 months or even longer, they can maintain bare ground for extended periods. While this can be a great advantage, use of these products prevents planting ornamentals on the site for a year or more after application. Plus, applications near the root system of desirable plants can damage trees and shrubs, so you must use caution when applying these chemicals. These chemicals also can injure certain turfgrass species, and movement of these chemicals down hillsides can cause yellow streaks in turf. Check labels to determine effectiveness on particular woody vines and to ensure you are adhering to all appropriate application instructions.
If you have a problem with woody vines in your landscape beds or in non-crop areas you maintain, identify the species first. Then evaluate the site and determine if sensitive vegetation is nearby. Spot-treat the vines with your chosen product and check for regrowth after a few weeks. Repeat treatments often are necessary to eradicate established vines. By scouting and using appropriate treatments with persistence, you can successfully manage woody vines in the areas you maintain.
Jeffrey Derr is associate professor of weed science at Virginia Polytechnic Institute and State University (VirginiaBeach, Va.).
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