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.
Many infestations of nonnative plants are too extensive or dense to permit selective herbicide applications, and instead require broadcast methods. Herbicides with appropriate selectivity can be used to minimize damage when native species are tolerant. Broadcast applications can be discontinued in pockets of nontarget native plants, where selective methods are more appropriate. In special plant habitats, small desirable plants can be protected by plastic covers during broadcast treatment. Broadcast sprays of herbicides without soil activity can be applied to evergreen or early greening invasives when native plants are dormant. Many equipment types are available for mounting broadcast application systems suitable for the situation.
Utility Skid and Trailer-Mounted Sprayers
Complete spray systems are available mounted on utility skids for hauling in truck beds and as trailers for towing behind many types of equipment. Sprayers for treating invasives often have a tank with 100- to 250-gallon capacity and require 100- to 200-foot hose reels attached to a handgun. A variety of handguns and nozzles allow applicators to adjust spray volume, distance, and pattern. Sprayer pumps are usually powered by 2-stroke gasoline engines that require availability of adequate fuel and oil onsite. Truck- and trailer-mounted sprayers are parked at a convenient location, from where the applicator walks with a sprayer handgun into the infestation. The chief benefit of mounted sprayers is their capacity for holding and applying high volumes of herbicide-water mixtures. But their benefit is checked by such limitations as accessibility to the infestation, hose length and weight, and provisioning of water in the field. Of mounted sprayers, the skid steer-mounted sprayer is best for getting into difficult terrain and stands.
 |
Basic Spraying Systems
Basic spraying systems for broadcast treatments have the following components: (1) tank, (2) pump, (3) strainer, (4) pressure regulator, (5) pressure gauge, (6) off and on valve, and (7) nozzle(s). Additional off and on valves are placed at convenient locations and additional strainers to protect components from undue wear. The spray tank should be equipped with an agitation system, or spray ingredients can be mixed in a separate mixing tank. For extended field operations, the system must include an additional water-supply tank equipped with a pump or gravity dispensing device.
All-Terrain Vehicle and Recreational-Type Vehicle Mounted Sprayers
ATV sprayers are best for selective applications in sensitive areas. Newly designed sprayers can hold 16, 24, or 40 gallons with optional front tank add-ons for many ATV models. Models have boom and/or boomless nozzles for broadcast application and a hose with spray gun for spot treatments. Recreational-type vehicles (RTVs) or Gators are larger than ATVs and carry a larger amount of herbicide mixture, with a capacity of up to 150 gallons. RTVs are a better option than ATVs for spraying rights-of-way and larger swaths of herbaceous plants, because the wide turn radius of RTVs makes them unsuitable for narrow areas. ATVs, with a tighter turn radius, are suited for repeated back-and-forth narrow swaths.
 |
 |
 |
Tractor-Mounted Sprayers
Spray systems can be mounted on farm tractors, four-wheel drive tractors, skidders, forwarders, and crawler tractors. Tractormounted sprayers are useful for large prairie and forest restorations as well as right-of-way projects. Interchangeable attachments allow the operator to use the tractor for herbicide application as well as for many other attachments such as seed drills. Tractor-mounted tanks have a capacity of 200 to 600 gallons of spray solution per tank, supporting a much larger workload than other ground equipment. Tractors have an assortment of implements that can be used not only for spraying for invasive plant control, but disking and seeding for restoration as well.
Spray nozzle systems for tractors are usually boomless, which means the spray streams are projected from the tractor. There are several boomless nozzle systems that range greatly in price and in control of spray pattern and droplet size.
The following is a list of boomless nozzle systems ranging from cheapest (with the most variable pattern and droplet control) to most expensive (with the most precise pattern and droplet control):
- 5880 Boom Jet® is a traditional, rugged, and inexpensive system. It consists of a cluster of five spray tips mounted on a circular head. Nozzles can be changed to match needs. Producing a very non-uniform spray pattern and range of droplet sizes, it is useful for treating shrubby invasives when an elevated mounting can gain spray height above the canopy.
- The Boom Buster Nozzle is an elongated off center nozzle of stainless steel with a gaping orifice opening from the end and running along the lower side. A nylon diffuser blade is positioned in the end of the orifice where a “hard edge” is formed for long-distance ejection of the spray solution. By mounting one or two nozzles perpendicular to the direction of tractor travel, the broad spray fans are directed to the side and behind the spray vehicle.
- Boominator® Spray Nozzle is a circular machined stainless steel nozzle designed for left or right mounting. This configuration extends side reach and provides a wide spray pattern with approximately 15 degrees kickback under the nozzle for coverage immediately behind the tractor.
- The Radiarc® Sprayer is a controlled droplet application system that produces droplets of uniform size. It uses direct electric power with rheostat adjustments to oscillate, in opposite directions, 2 circular heads of 11 tips each. It combines spray pressure (about 40 pounds per square inch) and centrifugal force to produce uniform droplets of large diameter for minimal drift. The 22 tips are evenly spaced around half the circular heads, producing semicircles of radiating spray that merge through oscillation behind and to the sides of the tractor. Spray pattern versatility is provided by a range of spray tip sizes. The system provides uniform pattern and droplet size, and can be elevated mounted where necessary to gain treatment height.
 |
 | |
 |
 |
 |
 |
 |
 |
Tractor-Mounted Wetblade and Cut-Spray Mower Applicators
Wetblade and cut-spray mowers are similar to “bush hogs” except herbicide is applied during or immediately after the cutting operation. One tractor-powered system dispenses herbicide onto the lower blade surface that wipes it onto the stems at the time of cutting. Control is inconsistent with this technology. Another system features an after-compartment behind the cutting deck that sprays herbicide onto the cut stems. The task of mowing and applying herbicides takes place in two specialized chambers. In the first chamber (the mower deck), the brush encounters a set of 6-inch blades capable of cutting stems 2 to 3 inches in diameter. The mowed debris is removed from the mowing chamber through a side discharge, not allowing the cut biomass to pass through the herbicide application chamber. Behind the mowing chamber is an enclosed herbicide chamber where the cut stubble encounters two treatment phases—a row of nozzles spray herbicide directly onto and through the stubble, not on the ground. Any herbicide that passes by the stubble is caught by an applicator consisting of scrapers, brushes, and chains; the applicator wipes herbicide onto the stubble in the second application stage. These systems assure precise herbicide application to the mowed area and prevent spray drift.
Wetblade mower systems also can deliver some biocontrol agents. Under certain conditions, this capability can integrate biological with mechanical control of invasives. Wetblade devices also can be added to normal brush saws for simultaneous cutting and treating of stumps.
Backpack Mist Blowers
Broadcast applications can be made with a gasolinepowered backpack mist blower. A wind turbine creates fine droplets that penetrate into shrubby stands and onto the foliage, but these droplets readily drift with wind and fog. As a safeguard to nontarget plants, foliar-active herbicides are usually recommended. These applications are only suitable for internal lands with dense infestations where drift of the mist-spray drops will be intercepted by target foliage and not move to nontarget plants or lands. Wind is critical for controlling this application. Wind must be minimal and moving away from a lane or spot of application into the target foliage. Applications must cease when gusts begin to occur. Privets have been treated successfully with this method in winter using a glyphosate herbicide when the hardwood overstory was mainly without leaves.
 |
Tractor-Mounted Weed Wick
Applicators consist of a wick or rope soaked with herbicide from a reservoir fed by a manual-use handle or electrical pump. The wetted wick wipes herbicide over the leaves and stems of herbaceous invasive plants as it passes over them. Rope-wick and canvas-wick applicators have been used for decades in crop management, especially to control Johnsongrass [Sorghum halepense (L.) Pers.] with glyphosate herbicides. Longitudinal rope-wick applicators are robust and provide a long contact time between wicks and individual plants. Both the backs and sides of plants are treated. Canvas-wick and transverse rope-wick applicators are less expensive but are easily damaged in rough terrain and only apply herbicide to the back side of the plants with short contact time.
Roadside Sprayers
Roadside sprayers are an array of specially designed and constructed sprayers for treating linear roadsides at relatively high speeds and with minimal wind drift. These spray systems are mounted on trucks and have 500- to 3,000-gallon spray and mixing tanks. Herbicide metering systems regulate herbicide dispersal rates in synch with truck speed. Integrated boomless nozzle systems consist of multiple nozzle arrays for treating different sections of road rights-of-way. Where this method is approved by State departments of transportation or county commissioners, roadside sprayers are effective against invasive plants on the outer edge of rights-of-way.
 |
Aerial Sprayers
Helicopter sprayers can apply herbicides on large or remote sites of extensive plant infestations. The helicopter blades can be folded for transport while mobile tanks with landing pads on top can permit operations from woods roads and openings. Helicopter applications to kudzu [Pueraria montana (Lour.) Merr.] infestations have been common and successful. More recently, dormant season helicopter applications of glyphosate have controlled Chinese privet growing in the shrub layer of hardwood forests absent of leaves. With GPS technology, helicopter applicators are extremely precise in treating target areas with preprogram swaths. They are highly maneuverable and apply sprays at much slower speeds than fixed-wing aircraft. Spray tanks vary in size from 90 to 230 gallons. Many types and sizes of nozzles are used, including control droplet and invert emulsion systems that minimize or eliminate spray drift. Contract aerial applicators are available in every part of the southern region.
Fixed-wing aircraft sprayers have spray booms mounted below the lower wing. With payload capabilities and airspeeds both greater than that of helicopters, fixed-wing aircraft sprayers have been effective in controlling brush and weeds in large areas since the 1950s. Spray tank capacities vary from 400 to 800 gallons. GPS/GIS systems are used for precision applications. Fixed-wing planes are not suited for spraying highly irregular-shaped sites or mountainous areas and require a nearby airport. Many herbicides are not labeled for application by fixed-wing aircraft.
Large fixed-wing aircraft applicators include specially modified C–130H aircraft and Modular Aerial Spray Systems (MASS). MASS are designed for specially modified C–130 aircraft that spray biting insects such as mosquitoes, sand fleas, and filth flies. The systems also control vegetation growth on military bombing ranges. Although such services are available nationwide, there are few management areas sizeable enough to utilize such a service in the Eastern United States. As an example, one project conducted by the 910th Airlift Wing, U.S. Air Force Reserve, in Youngstown, OH, sprayed 2,880,662 acres, or 4,501 square miles—an area equivalent to the State of Connecticut. Fourteen thousand gallons of pesticides were used, and the missions comprised 191.4 hours of total flying time with 46.5 hours of actual “spray-on” time flying at 150 feet aboveground level. Future use on military reservations and extensive invasive plant infested lands is possible, since the system has been perfected.
 |
