Miller, James H.; Manning, Steven T.; Enloe, Stephen F. 2010. A management guide for invasive plants in southern forests. Gen. Tech. Rep. SRS–131. Asheville, NC: U.S. Department of Agriculture Forest Service, Southern Research Station. 120 p.
Although treating extensive infestations may require broadcast treatments of herbicide sprays or pellets by helicopter or tractor-mounted application systems, the best approach is usually selective applications to target nonnative plants while avoiding or minimizing application to desirable plants. The selective methods described below are directed foliar sprays and wipes, basal sprays and wipes, stem injection, cut-treat, basal sprays, and soil spots.
Directed Foliar Sprays and Wipes
Directed foliar sprays are herbicide-water-adjuvant solutions aimed at target plant foliage to wet all leaves, applied by either low- or high-volume sprayers. Herbicide application by directed foliar spray is one of the most cost-effective methods for treating many types of herbaceous and woody invasive plant species. With this method, herbicide mixtures are applied to the foliage and especially the growing tips of woody plants, or to completely cover herbaceous plants. Foliar sprays can be applied whenever leaves are present but, for woody plant control, are usually most effective from midsummer to late fall. Winter and spring applications are also effective in controlling specific species and are often required to prevent seed formation.
Selective treatment is possible because the applicator can direct the spray towards target plants and away from desirable plants. The addition of a spray shield to the end of the wand confines spray to the target. Another safeguard is to only use foliar-active herbicides, because directed sprays of soil-active herbicides can damage or kill surrounding plants when their roots are within the treatment zone. Never use herbicides with soil activity to treat invasive plants under desirable trees or shrubs that are susceptible to the herbicide. If nontarget foliage is accidently sprayed, clip off the foliage to prevent uptake.
Low-volume foliar sprays using spray tips and spraying pressures of 20 to 30 pounds per square inch can ensure productivity and limit drift to surrounding plants. Plants up to 6 feet tall can be treated with this equipment, while the addition of a commercially available wand extension can slightly increase height capabilities. To treat plants up to about 18 feet tall, use higher spray pressures with a straight-stream or narrow flat-fan tip. Wind must be minimal (less than 2 miles per hour) and used by the applicator to facilitate upper crown coverage. A handgun with a rollover valve can replace the spray wand and accommodates two tips, such as a flat fan for close spraying and a narrow flat fan or adjustable cone nozzle for tall plant spraying. This setup greatly extends applicator capabilities and productivity when invasive infestations vary in height. Sturdy metal wands can replace plastic ones for more precise applications. Small booms with multiple nozzles can replace the single-nozzle wand for better productivity and efficiency in treating large areas of low-growing invasives. Directed foliar sprays can be applied in higher volumes by using spray wands attached by hoses to vehicle-mounted spraying systems that have much larger herbicide tank capacities. The high-volume directed foliar spray is the most efficient approach to large infestations of multiple invasive species where there are few nontarget plants.
Handheld weed wicks and rollers apply ultra-low volumes by wiping the herbicide mix onto the target leaf surfaces or bark; the herbicide mixture is contained in the handle. A few commercial models are manufactured in Australia and New Zealand, but devices also can be handmade from PVC tubing, fittings, and a sealed on sponge or rope wick and fitted to the wand of a backpack sprayer. Most wick systems have limited use and durability in forest and field situations, but are useful when the applicator needs to avoid applying herbicide to rare or protected plants. Similar to a weed wick applicator, a rolling sponge head is another drift-free tool option that allows application directly to targeted species.
The THINVERT Application System uses a series of special spray nozzles to apply thin invert emulsion spray solutions (thin mayonnaiselike consistency) to greatly reduce drift and evaporation of spray particles on the plant surface. The nozzles and a combination of special oil soluble herbicide (triclopyr) and emulsifying agent have been developed and sold by Arborchem Products Company (717–766–6661, www.arborchem.com). This system combines the unique spray nozzle and spray carrier into a coordinated unit for aerial or ground applications to roadsides, rangeland, cropland, industrial sites, forests, and landscape areas. Thinvert sprays can be applied to foliage as well as stems or cut-stumps where absolutely no drift can be tolerated, such as immediately adjacent to neighboring croplands and special rare plant habitats.
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Basal Sprays and Wipes
Basal sprays are herbicide-oil-penetrant mixtures sprayed on the lower portion of woody shrub, vine, and tree stems. The sprays are usually applied with a backpack sprayer or wick applicator. Basal sprays are best where most trees are less than 8 inches diameter breast height (d.b.h.), but can be used on much larger trees of susceptible species. Application is to smooth juvenile bark by thoroughly wetting the lower 12 to 20 inches of the trunk, up to 36 inches on larger trees to the groundline including the root-collar area and any exposed roots. Smaller trees and shrubs are controlled with less coverage. Avoid spray contact with desirable trees or heavy use within their root zone.
The herbicide must be an oil-soluble formulation, such as Garlon 4 and Stalker, and mixed with a special basal oil product, penetrating oil, diesel fuel, fuel oil, mineral oil, vegetable oil with a penetrant, or blends of these ingredients. Appropriate oils will be specified on the label. Some oils may be prohibited for application in riparian areas and wetlands. Use an adjustable cone nozzle with a coarse spray. For less off-target spray on smaller trees, use an even flat-fan nozzle with a fairly narrow angle and low volume (such as a 4002E, oriented crosswise to the wand for a spray that lands in a vertical band on the stem).
Some herbicides, such as Pathfinder II and Vine-X (triclopyr herbicides), are sold ready to use with these oils. Vine-X is sold in an applicator bottle with a brush tip suitable for gardeners and homeowners.
A modified method, streamlined basal sprays, is effective for many woody species up to 2 inches in groundline diameter and susceptible species up to 6 inches in diameter, such as privets. Equipment for this treatment is a backpack sprayer with a spray gun and a low-flow straight-stream or narrow-angle spray tip. To prevent waste, maintain pressure below 30 pounds per square inch with a pressure regulator. At this pressure, an effective reach of 9 feet is possible while bark splash is minimized. For treating stems less than 2 inches in diameter, apply the stream of spray up and down single stems for about 6 to 8 inches or apply across multiple stems in 2- to 3-inch-wide bands. This multiple-band treatment also can be effective on larger stems. Direct the spray stream to smooth juvenile bark about 4 to 18 inches from the ground and below branches. Stems that are thick barked or near 3 inches in diameter require treatment on all sides.
The most effective time period in most of the South for a basal spray and streamline is June through September, while winter treatments are easier when leaves do not block access and spray. Fall, winter, and late spring applications are often not as effective, though the period from February 15 to April 1 has shown acceptable results. After treating with a basal spray, wait at least 6 months before cutting dead trees, because herbicide activity within plant roots can continue for an extended period.
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Stem Injection
Stem injection (including hack-and-squirt) involves herbicide concentrate or herbicidewater mixtures applied into downward incision cuts spaced around woody stems. Cuts are made by an ax, hatchet, machete, brush ax, cane knife, or a variety of cutting tools and even cordless drills. Tree injection is a selective method of controlling larger trees, shrubs, and vines (greater than 2 inches in d.b.h.) with minimum damage to surrounding plants. Stem injection is the fastest and most cost-effective method for nonnative trees and large shrubs. Injection treatments are sometimes not as effective in controlling multiple-stemmed species compared to the faster basal bark treatments, but may be easier in remote or rough terrain where a backpack sprayer might be impractical or cumbersome. Stem injection is physically demanding for the applicator, who must repeatedly and accurately strike target trees with a sharp tool before delivering the herbicide into the cut. For best results, sharpen tools frequently.
Incisions must be deep enough to penetrate the bark and inner bark, slightly into the wood. Do not make multiple cuts directly above or below each other because this will inhibit movement of the herbicide within the stem. A complete girdle or frill of the stem is not needed or desirable. Space the injection cuts 1 to 1.5 inches apart edge to edge (or per label instructions) around the circumference of each trunk individually or within a clump at a convenient height. Use a handheld, chemical-resistant 1- to 2-quart spray bottle to apply 0.5 to 2 mL of concentrated herbicide or dilutions (prescribed on the label) into the cut. The amount will depend on the size of cut and how much the cut can hold without the herbicide running onto the bark. Apply herbicide to each cut until the exposed area is thoroughly wet. The herbicide should remain in the injection cut to avoid wasting herbicide and to prevent damage of surrounding plants. All injected herbicides can reach untreated plants by root grafts between like species, and uptake of root exudates by all species results in nontarget damage. Herbicides with soil activity can damage nearby plants when washed from incisions into the soil by unexpected rainfall soon after application. Avoid injection treatments if rainfall is predicted within 48 hours.
Special tree injectors are available that combine the cutting operation with automated herbicide delivery. For injecting some herbicides (amine formulations), the Hypo- Hatchet® Tree injector (Forestry Suppliers Inc., 800–647–5368, www.forestry-suppliers. com) consists of a steel hatchet connected to a herbicide container (worn on belt) by tubing. The injector delivers a set amount of herbicide into the cut. Daily cleaning and lubrication of the impact piston is required maintenance, along with periodic replacement of rubber o-rings and seals. Check all hoses and fittings before use for leaks and make appropriate repairs to prevent accidental exposure of herbicide to the applicator. When working with the Hypo-Hatchet in dense infestations, be mindful of the supply tubing, which might become tangled and easily disconnected.
Another injector is the EZ-Ject®, which consists of a steel lance that holds 400 shells of glyphosate or imazapyr herbicides (ArborSystems, 888–395–6732, www.ezject. com). The head of the lance is placed against the base of the target woody plant, and a manual thrust jams the shell through the bark into the inner bark. As with other injection methods, these shells are spaced around each stem. The EZ-Ject is the most efficient and effective injection option for treating multi-stemmed, low-branching shrubs like privets, silverthorn (Elaeagnus pungens Thunb.), and bush honeysuckles (Lonicera spp.), as well as large entangled vines like oriental bittersweet (Celastrus orbiculatus Thunb.). Shell jamming has been reported as a problem when using the EZ-Ject to treat extensive infestations. Removing the herbicide shells when not in use, proper use, and daily maintenance can help prevent jamming.
Tree injection can be applied at most times throughout the year, but December to the middle of January seems to be least effective in the Midsouth. Prolonged cold temperatures can freeze herbicide in the cut, resulting in poor absorption. Heavy spring sapflow can wash herbicide from incision cuts, resulting in poor control and soil transfer to nontarget plants. Prolonged and severe drought is also an ineffective period.
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Cut-Treat
Cut-treat involves applying herbicide concentrates, herbicide-water or herbicide-penetrant mixtures to the outer circumference of freshly cut stumps or the entire top surface of cut stems. Applications are made with a spray bottle, backpack sprayer, wick, or paint brush. Freshly cut stems and stumps of trees, woody vines, shrubs, canes, and bamboo stems can be treated with herbicide mixtures to prevent resprouting and to kill roots. It is critical that the cut is made as low as possible to the ground, and that the stem is treated immediately after the cut is made. Invasives not treated with herbicides after cutting invariably resprout and intensify their infestation. Cutting is usually by chainsaw or brush saw but can be made by handsaws and cutting blades.
To minimize deactivation of the herbicide in the cut-treat method, remove sawdust from stumps before treatment. For stumps over 3 inches in diameter, completely wet the outer edge with the herbicide or herbicide mixture. Make certain that the solution thoroughly covers the wood next to the bark of the stump. Completely wet the tops of smaller stumps and all cut stems in a clump. Apply a basal spray mixture of herbicide, oil, and penetrant to stumps that have gone untreated for over 2 hours. Make certain to wet stump sides and root collar to further prevent sprouting.
The most effective time for the cut-treat method has not been determined for all invasive species, while summer and fall have shown to provide good control. One-year research results show that spring cut-treat with Garlon 4 on large Chinese privet is completely effective. Although winter treatments are slightly less effective than growing season applications, the absence of foliage on some cut stems and branches produces some offsetting gains in application efficiency.
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Hand Sprayers for Injection and Cut-Treat
Most commercial hand sprayers are for occasional weekend household use. If you require a model for heavier duty and continuous daily operations, consider a sprayer with chemical-resistant Viton seals and a manual handpump. A good hand sprayer also will have an adjustable mist nozzle and a large filling opening. Models with a pump compression design are good for cutting and treating, while trigger-action pumps are better suited for stem injection or soil spot treatments. A full-grip valve will prevent fingertip fatigue with prolonged daily use of finger trigger valves.
Handsaws or Cutting Blades
Chainsaws
A chainsaw with a 12- to 14-inch bar is best for felling most woody invasive plants since they are light weight and suited for cutting multiple stems in clumps. Professional tree saws are usually the lightest on the market and the tool of choice among contractors.
Brush Saws
Brush saws are large gasoline-powered weed eaters with a circular saw blade for cutting woody stems. While many large and expensive brush clearing saws are on the market, the high-end professional model is the preference of contractors for large projects. Special chainsaw-like tooth blades around a disc are the most efficient for cutting invasive plants and can be sharpened in the field throughout the life of the blade.
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Soil Spots
Spots of soil-active herbicides (mainly Velpar L and Hyvar X-L) are applied as spaced metered amounts around target woody stems or in a grid pattern for treating many stems in an area. Spots are usually applied with a utility spray bottle (herbicide-resistant seals preferred) or with operator-timed pulses from a hand sprayer or backpack sprayer equipped with a straight-stream nozzle. This method requires attention to preparing exact amounts and making prescribed spacings in strict accordance with specifications on herbicide labels or label supplements. It is effective only on specific nonnative plant species and usually only in spring and early summer. Any desirable plant with roots in the spot area can be killed or injured, making this appropriate only for dense infestations of a single invasive species such as tallowtree [Triadica sebifera (L.) Small], bamboos (Phyllostachys spp. and Bambusa spp.), and Brazilian peppertree (Schinus terebinthifoliu Raddi). Loblolly pine (Pinus taeda L.) is tolerant to Velpar L, and, thus, can be released from susceptible invasive shrubs and trees.
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Under Development: Pneumatic Applicator for Herbicide
Ballistic Technology
New equipment options under development for invasive plant management include paintball guns with herbicide-filled ammunition for basal applications. Researchers at the University of Hawaii are studying how paintball guns might help selectively control a variety of species in hard-to-reach areas. From the ground or helicopter, sharpshooters can apply herbicides in a very selective manner with this tool.
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