SHRUBS & SUBSHRUBS

CONTROL OPTIONS

GENERAL GUIDANCE FOR MOST SHRUBS

Use pesticides wisely: always read the entire pesticide label carefully, follow all mixing and application instructions and wear all recommended personal protective gear and clothing. Contact your state department of agriculture for any additional pesticide use requirements, restrictions or recommendations. Notice: mention of a trade name does not constitute the endorsement of the product by authors, agencies or organizations involved in the production of this publication.

Chemical
Two of the more widely used systemic herbicides are glyphosate and triclopyr. Systemic herbicides are absorbed by plant tissues and carried to the roots causing the entire plant to die usually within about a week. Glyphosate is a non-selective herbicide that may kill or harm any plants that come in contact with the spray. It carries a Caution signal word and requires long-sleeved shirt, long pants, shoes and socks during application. Glyphosate products referred to in this publication are sold under a variety of brand names (Accord®, Rodeo®, Roundup Pro® Concentrate) and in three concentrations (41.0, 50.2 and 53.8% active ingredient). Other glyphosate products sold at home improvement stores may be too dilute to obtain effective control.

Triclopyr is a selective herbicide that affects only broadleaf plants (e.g., forbs, shrubs and trees) and can be used in grasslands or areas where desirable grasses are growing under or around targeted woody or broad-leaved invasives. Use of triclopyr in areas where soils are permeable, particularly where the water table is shallow, can result in groundwater contamination. Triclopyr comes in two forms – triclopyr amine (e.g., Garlon® 3A, Brush-B-Gone®, Brush Killer®) and triclopyr ester (e.g., Garlon® 4, Pathfinder®, and Vinex®). They are very different products with very different specific uses, hazards and precautions. Triclopyr amine mixes with water and can be used near water without posing a threat to aquatic organisms and can be used as a cut stem treatment at a 50% rate or a foliar treatment at 5% rate. It is not effective for basal bark treatments. However, the amine form of triclopyr carries a Danger signal word due to its corrosive properties which, in concentrated form, can cause irreversible eye damage. For this reason, it should only be used by trained and certified applicators who are familiar with this hazard and know the precautions that need to be taken when using it.

The ester form of triclopyr (e.g., Garlon® 4) carries a Warning signal word for the potential to cause skin and eye irritation but is not known to cause irreparable eye damage. Because it is toxic to aquatic invertebrates, it cannot be used near water or in wet soils. Garlon® 4 can be used for foliar, cut stem and basal bark applications. Due to the high potential for volatilization and offsite drift, triclopyr should not be used when the temperature is above 85°F. Drift can result in kill of non-target trees and other woody vegetation. It is imperative that protective eyewear and chemical resistant gloves be worn in addition to long-sleeve shirt, long pants, shoes and socks, during mixing and application. Always read the entire label before using any pesticide.

Basal Bark Method: This method is effective throughout the year as long as the ground is not frozen. While reducing the total amount of herbicide mixture applied to the environment, it requires a much more concentrated mix than that used for foliar applications. Prepare a mixture of 25% triclopyr plus 75% horticultural oil and apply to the basal parts of the shrub to a height of about a foot from the ground. Thorough wetting is necessary for good control; spray until run-off is noticeable at the ground line. A dye added to the mixture will help keep track of treated plants.

Cut Stem Method: This method and basal bark should be considered when treating individual plants or when target plants are mixed in with desirable species which would preclude foliar treatment. It is usually effective as long as the ground is not frozen. As with basal bark treatment, it reduces the total amount of herbicide mixture applied to the environment but requires use of a much more concentrated mix than that used for foliar applications. Cut stems at or near ground level and immediately apply a 25% solution of glyphosate or triclopyr mixed in water to the cut stump surface, making sure to cover the entire surface. As with basal bark, a dye added to the mix will help keep track of treated plants.

Foliar: Because this method involves applying herbicide mix to foliage (leaves), it should be considered mostly for large infestations where the risk to non-target species is minimal. The best time to treat is late fall or early spring when targeted plants are shifting resources toward the roots and many native species are dormant. Foliar application can be done almost anytime but air temperature should be above 65°F to ensure absorption of the herbicide mix. To allow ample drying time applications should be made when rain is unlikely for about 12 hours after application and leaves should be dry prior to treatment. Wind speed should be below 8-10 mph to avoid off-site drift. Apply a 2% solution of glyphosate or triclopyr and water plus a 0.5% non-ionic surfactant to thoroughly wet all leaves. Mix should not be dripping off leaves. Use a low pressure and coarse spray pattern to reduce spray-drift damage to non-target species. To avoid drift, triclopyr and glyphosate should be applied when winds are below about 8 mph. If desirable trees are nearby, a no-spray buffer area should be established to protect non-target plants.

Manual
Hand pulling is an effective method for many shrubs when in the young seedling stage, after which a tool or other method is often needed to remove strong roots. Plants should be pulled as soon as they are large enough to grasp but before they produce seeds. Seedlings are best pulled after a rain when the soil is loose. Larger stems, up to 6 cm (2½ in), can be removed using a Weed Wrench® or similar uprooting tool. For most species, the entire root should be removed to avoid resprouting.

Mechanical
Cutting or mowing is appropriate for small infestations or environmentally sensitive areas where herbicides cannot be used. It is not generally recommended for plants that resprout heavily unless cutting can be repeated and plants monitored until the targeted invasive has been eliminated. Ideally, cutting is most effective when combined with an application of herbicide to cut surfaces. Stems should be cut at least once and preferably multiple times per growing season and as close to ground level as possible.

AMUR HONEYSUCKLE

See General Guidance.

AUTUMN OLIVE

See General Guidance.

Basal bark. Seedlings, saplings, and mature trees can be killed using triclopyr ester (e.g. Garlon® 4) as a basal bark treatment which is very effective. This method involves spraying herbicide directly onto the lower 2 feet of each stem with triclopyr (e.g. Garlon® 4 or Remedy™). It minimizes soil disturbance and maintains other desirable vegetation. Applications should completely wet the entire circumference of all stems or clumps of stems, but not to the point of run-off. For saplings, apply Garlon® 4 as a 20 percent solution (2.5 qts. per 3 gal. water) in horticultural oil with a penetrant (check with herbicide distributor) to young bark as a basal spray.

Cut stump. First cut the stem/trunk as close to the ground as possible, then immediately (within a few minutes) brush-on or squirt a 50% Garlon® 4 onto the cambium layer of the cut-stump. This can also be done as a hack and squirt type application.

Foliar. This method works well on seedlings and saplings and works best when applied July to October. These are directed spray treatments with limited soil activity. Thoroughly wet all leaves with a glyphosate-based herbicide (e.g., Accord®) or triclopyr-based herbicide (Garlon® 4) as a 2-percent solution (8 oz. herbicide per 3 gal. water) with a surfactant.

JAPANESE BARBERRY

Chemical
See General Guidance.

Because Japanese barberry leafs out early, it is easy to identify and begin removal efforts in early spring. Small plants can be pulled by hand, using thick gloves to avoid injury from the spines. The root system is shallow making it easy to pull plants from the ground, and it is important to get the entire root system. The key is to pull when the soil is damp and loose. Young plants can be dug up individually using a hoe or shovel. Hand pulling and using a shovel to remove plants up to about 3 ft. high is effective if the root system is loosened up around the primary tap root first before digging out the whole plant. Mechanical removal using a hoe or Weed Wrench® can be very effective and may pose the least threat to non-target species and the general environment at the site. Tools like the Weed Wrench® are helpful for uprooting larger or older shrubs. Shrubs can also be mowed or cut repeatedly. If time does not allow for complete removal of barberry plants at a site, mowing or cutting in late summer prior to seed production is advisable.

JAPANESE MEADOWSWEET

See General Guidance.

Japanese meadowsweet resprouts after cutting, making repeated cutting necessary to exhaust the plants energy reserves. Stems should be cut at least once per growing season, prior to seed production, and cut as close to ground level as possible.

LINDEN VIBURNUM

See General Guidance.

Cutting should be avoided in spring because cut branches can reproduce by layering (when a new plant forms from development of roots on a stem attached to the parent plant). Use of systemic herbicides like glyphosate or triclopyr will prevent resprouting. Seedlings can be pulled up by hand. Seed heads should be removed from mature plants to prevent seed dispersal and seedling establishment.

MORROW’S HONEYSUCKLE

See General Guidance.

MULTIFLORA ROSE

See General Guidance.

Biological
Biological control is not yet available for management of multiflora rose. However, researchers are investigating several options, including a native viral pathogen (rose-rosette disease), which is spread by a tiny native mite, and a seed-infesting wasp, the European rose chalcid. Rose-rosette disease, native to the western U.S., has been spreading easterwardly at a slow pace. It may hold some potential for eliminating multiflora rose in areas where it grows in dense patches.

PRIVETS

See General Guidance.

WINGED BURNING BUSH

See General Guidance.

 

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Last updated:11-Nov-2010