TREES

CONTROL OPTIONS

GENERAL GUIDANCE FOR TREES

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.

While removal of young plants or cutting of some trees may be effective for some species, the most effective method for control of invasive tree species involves the use of systemic herbicides. Herbicides which may be applied as a foliar (to the leaves), basal bark, cut stump, or hack-and-squirt treatment. Always be careful with herbicide applications in the vicinity of desirable native plants or valuable ornamental shrubs and trees.

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 is one of the easier methods available, does not require any cutting, uses a small amount of herbicide mix and is effective throughout the year as long as the ground is not frozen. It works best during late winter/early spring and in summer. The base of the tree must be free of snow, ice, or water on the bark from recent rainfall, though precipitation following application is inconsequential. Late winter/early spring (February 15 -April 15, Mid-Atlantic) is generally the most productive time, since vegetation near the base of the trees is usually absent or leafless. Late spring and early summer applications (April 15-June 1 in the mid-Atlantic), when plant fluids are moving upwards to support new growth, are usually not as effective. Application during the summer (June 1-September 15) works very well as long as vegetation is not a hindrance, and allows lower concentrations of herbicide to be used. Fall to mid-winter applications (October-January) may be less effective and temperatures below 45ºF will restrict the use of triclopyr.

Mix up a solution of 20% (as low as 10% in summer depending on objectives) concentration of oil-soluble triclopyr product (e.g., Garlon® 4) in 80% oil (mineral oil, or special vegetable oils). A dye added to the mixture will help keep track of treated plants. Some applicators add a pine oil-based additive (e.g., Cide-Kick® II) at the rate of 10%, which helps penetrate the bark and eliminate unpleasant odor. Some companies market diluents based on mineral or vegetable oils specifically designed for basal bark application, which should be considered for use in sensitive areas. Another option is to use a pre-mixed, ready-to-use triclopyr product designed for basal bark (and cut stump) application (e.g., Pathfinder® II). Using a handheld or backpack sprayer, apply the mixture in a 12-inch wide band around the entire circumference of the tree base with no “skips.” The basal bark method is generally used for trees that are less than 6 inches in diameter, though slightly larger stems may also be treated effectively by thoroughly treating bark up to 24 inches in height. Follow-up foliar application (see above) to basal sprouts and root suckers may be necessary, depending on the species.

Cut Stem Method: This method is useful in areas where the trees need to be removed from the site and will be cut as part of the process. While situations exist that dictate this method over the others given above, felling trees is usually less effective in killing the root system, slower, more labor intensive, and more hazardous to personnel than other methods. This method is likely to be most successful during the growing season, with diminishing success through the early fall. Dormant season applications may prevent resprouting from the stump itself, but will do little to inhibit root suckering. However, at any time of year, if the tree must be cut it is better to treat the stump than not.

Cut trees near ground level and immediately apply a 25% solution of glyphosate mixed with water or 20% Garlon® 4 plus 80% oil dilutant, to the whole cut stump surface and the sides to the ground line. As with basal bark, a dye added to the mix will help keep track of treated plants. The mixture may be painted on with a paint brush or sprayed on using a spray bottle or backpack sprayer. Application of herbicide to the cut stumps must be conducted immediately after cutting, within 5-15 minutes of the cut with water soluble formulations, longer with oil mixtures, to ensure uptake of the chemical before the plant seals the cut area off.

Foliar: Because this method involves applying herbicide mix to foliage (leaves), it should be considered for small dense infestations or for large infestations where the risk to non-target species is minimal. Foliar treatment can be very effective but requires use of larger volumes of herbicide mixture and increases the risk of non-target impacts. Limitations of the method are the seasonal time frame and the need to transport a larger, more dilute mixture. It is typically more effective in summer and late season when plants are shifting resources downward to roots.

For most plants, use a 2% rate of glyphosate mixed with water and a small amount (0.5%, or as per label) of a non-ionic surfactant (except for Roundup®, which contains a surfactant) to help the spray spread over and penetrate the leaves. A 1.5% rate (4 lb./gal.) triclopyr (Garlon® 4) can also be used in this way. The mixture should be applied to leaves and green stems, including sprouts and suckers, until thoroughly wet but not to the point of runoff. Use a low pressure and coarse spray pattern to reduce spray-drift damage to non-target species. To avoid drift, applications should be made 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.

Foliar application can be done almost anytime as long as air temperature is above about 65°F (and no higher than 85°F for triclopyr) to ensure absorption of the herbicide. To allow ample drying, 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.

Hack-and-squirt or injection. This method can be very effective and is useful when target trees are mixed in with desirable trees. it requires using a hand axe to make downward-angled cuts into the sapwood around the tree trunk and squirting about a teaspoon of concentrated herbicide into the cut.

Manual
Young seedlings may be pulled or dug up, preferably when soil is moist. Care should be taken to remove the entire plant including the roots whenever possible to avoid the possibility of regrowth through sprouting.

Mechanical
Cutting can work for many trees unless they are likely to resprout. It will need to be done continuously until the plants are no longer found.

CALLERY PEAR

See General Guidance.

NORWAY MAPLE

See General Guidance.

PAPER MULBERRY

See General Guidance.

PRINCESS TREE

See General Guidance.

SILK TREE

See General Guidance.

TREE OF HEAVEN

See General Guidance.

Elimination of tree of heaven requires diligence, due to its abundant seed production, high seed germination rate, and vegetative reproduction. Followup monitoring and treatment when needed should be an integral part of any serious ailanthus management program. Regardless of method selected, treated areas should be rechecked one or more times a year and any new suckers or seedlings treated (cut, sprayed or pulled) as soon as possible, especially before they are able to rebuild root reserves. Establishing a thick cover of trees (non-invasive and preferably native) or grass sod will help shade out and discourage establishment of ailanthus seedlings. Targeting large female trees for control will help reduce spread of ailanthus by seed.

Biological
Several fungal pathogens are being investigated as potential agents for biological control for tree-of-heaven. Two of these, Verticillium dahliae and Fusarium oxysporum, have been isolated from dead and dying tree of heaven in New York and in southern and western Virginia. Another fungal pathogen, Verticillium albo-atrum, was recently confirmed using inoculations in the lab and on canopy field trees to be the cause of Ailanthus wilt disease that killed more than 8,000 trees in south-central Pennsylvania since 2002. Research and testing are on-going and none are available at this time.

Chemical
The most effective method of ailanthus control is through the use of herbicides, which may be applied as a foliar (to the leaves), basal bark, cut stump, or hack and squirt treatment. While it is relatively easy to kill the above ground portion of tree of heaven, you need to kill or seriously damage the root system to prevent or limit stump sprouting and root suckering. Always be extremely careful with herbicide applications in the vicinity of valuable ornamental shrubs and trees.

Foliar application. See General Guidance. Foliar sprays applied when trees are in full leaf are very effective, and should be the method of choice where ailanthus size and distribution allow effective spray coverage of all foliage without unacceptable contact with nearby desirable vegetation or applicator. Where it growing in association with other exotic weed species, as is often the case, foliar spray allows treatment of the entire area at one time. Use either glyphosate or triclopyr mixed with water and a small amount (0.5%, or as per label) of a non-ionic surfactant (except for Roundup®, which already contains a surfactant) which will help spread the mix and penetrate the leaves. Apply the mixture to leaves and green stems, including sprouts and suckers, until thoroughly wet but not to the point of runoff. For backpack sprayer applications, 2% glyphosate (e.g., Roundup, Accord) applied June 15 to Sep. 15 has worked well in the mid-Atlantic region. For higher volume applications using a truck-mounted sprayer, concentration can be reduced to 1 or 1.5%. Other herbicides which have shown to be effective as foliar treatment of Ailanthus include imazapyr (e.g., Arsenal®, Chopper®), and metsulfuron methyl (e.g., Escort®), but these products are not discussed further here.

Basal bark method. This method works best during late winter/early spring and in summer. The base of the tree stem must be free of snow, ice, or water on the bark from recent rainfall, though precipitation following application is inconsequential. Late winter/early spring (February 15 -April 15, Mid-Atlantic) is generally the most productive time, since vegetation near the base of the trees is usually absent or leafless. Late spring and early summer applications (April 15-June 1, Mid-Atlantic), when plant fluids are moving upwards to support new growth, are questionable. Application during the summer (June 1-September 15, Mid-Atlantic) works very well as long as vegetation is not a hindrance, and allows lower concentrations of herbicide to be used. Fall to mid-winter applications (October-January) have given poor results. Mix up a solution of 20% (as low as 10% in summer depending on objectives) concentration of oil-soluble triclopyr product (e.g., Garlon® 4) in 80% oil (mineral oil, or other recommended vegetable oils but not diesel or other fuels that can pollute groundwater). With these diluents some applicators add a pine oil based additive (e.g., Cide-Kick® II) at the rate of 10%, which helps penetrate the bark and eliminate any unpleasant odor. Some companies market diluents based on mineral or vegetable oils specifically designed for basal bark application, which should be considered for use in sensitive areas. Using a handheld or backpack type sprayer, apply the mixture in a 12 in. wide band around the entire circumference of the tree base with no “skips”. The basal bark method is generally used for trees that are less than 6 inches in diameter, though slightly larger stems may also be treated effectively by thoroughly treating bark up to 24 in. in height. Follow-up foliar herbicide application (see above) to basal sprouts and root suckers may be necessary. Another herbicide which has been shown to be effective for basal bark control of ailanthus is imazapyr (e.g., Chopper®, Stalker®). This is sometimes used in a combination with triclopyr at a concentration of 15% Garlon® 4 and 5% Stalker® in 80% oil dilutant.

Hack-and-squirt or injection. This method is very effective and minimizes sprouting and suckering when applied during the summer. Root suckering will be an increasing problem in the fall, winter and spring. The method requires first making downward-angled cuts into the sapwood around the tree trunk at a comfortable height, using a hand ax. With spray bottle or wand in the other hand, a straight (100%) concentration of a water-soluble triclopyr product (e.g., Garlon® 3A) is applied into the cuts within a minute or two of cutting, applying 1-2 milliliters into each cut (typically 1-2 squirts of a trigger squirt bottle) so that the bottom of the cut is covered, but liquid doesn’t run out of it. Generally, you would make about 1 hack cut for each inch of diameter plus one (i.e., for a 10 in. diameter tree, make about 11 cuts). Space the cuts so that about 1-2 in. of uncut living tissue remains between them. A continuous line of cuts around the trunk would likely cause the tree to go into emergency response mode and react by producing basal sprouts and root suckers. For this reason, girdling or frilling (girdling followed by herbicide) is not recommended for Ailanthus unless long term follow-up treatment is possible. This method can be used with trees of any size, though it is most productive with stems over 2 in. in diameter. This method is relatively easy for one person to do, with hatchet in one hand and spray bottle in the other, but should be done with a buddy nearby in case of an accident. Monitor the treatment area and be prepared to follow-up with a foliar application the next year to control any basal sprouts or root suckers that might emerge. Glyphosate products have sometimes been recommended for control of ailanthus using this method, but field trials have shown consistently poor long-term control of basal sprouts and root suckers at any time of year.

Cut stump. See General Guidance. Use this method when trees need to be removed from the site and will be cut as part of the process, Effectiveness is likely to be better during the growing season, with diminishing success through the early fall. Dormant season applications may prevent resprouting from the stump itself, but will do little to inhibit root suckering. However, at any time of year, if the tree must be cut it is better to treat the stump than not. Application of herbicide to the cut stumps must be conducted immediately after cutting, within 5-15 minutes of the cut with water soluble formulations, longer with oil mixtures, to ensure uptake of the chemical before the plant seals the cut area off. The mixture may be painted on with a paint brush or sprayed on using a spray bottle or backpack sprayer. A mixture of 20% Garlon® 4 plus 80% oil dilutant, as for basal bark spraying (above), may be used. In this case the whole stump surface and sides to the ground line would be sprayed. Be prepared to follow-up with a foliar application the next year to control any stump sprouts or root suckers which emerge. Other herbicides which have been shown to be effective in stump treatment of ailanthus are the same as those listed above for hack and squirt or injection but are not covered in this book.

Manual
Young seedlings may be pulled or dug up, preferably when soil is moist. Care must be taken to remove the entire plant including all roots and fragments, as these will almost certainly regrow. Root suckers appear similar to seedlings, but would be connected to a pre-existing lateral root, and would be nearly impossible to remove effectively.

Mechanical
Cutting alone is usually counter-productive because ailanthus responds by producing large numbers of stump sprouts and root suckers. However, for small infestations, repeated cutting of sprouts over time can exhaust the plants reserves and may be successful if continued for many years or where heavy shade exists. If possible, the initial cutting should be in early summer in order to impact the tree when its root reserves are lowest. Cutting large seed producing female trees would at least temporarily reduce spread by this method.

WHITE MULBERRY

See General Guidance.

 

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Last updated:11-Nov-2010