Application Technology

Treatment Area Parameters

There are numerous factors involved in establishing a treatment area or even an individual ‘spray block’ within the treatment area.

Entomological factors include the type of insect, the history of the infestation, and the amount of defoliation that is predicted to occur in the area until the insect populations collapse naturally or some other intervention (spraying, cutting, fire, etc) occurs. Other issues include the ecological and economic significance of the areas to be protected, access to the forested area by the public and program staff, proximity to water bodies or other natural features etc

Once a decision has been made to protect a forest from the current defoliator pest, then a myriad of other factors must considered in the decision making process.

These factors include adherence to local regulations, the choice of insecticide, the potential need for buffer zones and/or ‘No Spray’ zones, the cost of protection, the availability of financial and other resources to conduct the protection program, access to the treatment area, choice of aircraft etc.

Adult stage Source: Dave Powell, USDA/FS,

No Spray Zones are areas not to be treated during the protection program; this may be as simple as visible water bodies or they may be established due to specific ecological concerns such as threatened and endangered lepidopteran species, the presence of organic crops within or adjacent to the treatment area, and non-host forest type within the proposed treatment area.

Buffer Zones are sometimes included as an operational requirement to reduce the potential for the insecticide to be deposited within a specific geographic area. Buffer zones will not be necessarily be ‘a pesticide free zone; their purpose is merely to provide some lateral distance from the treatment area to ‘buffer’ or reduce any potential impacts due to the treatment.

Choice of Insecticide

Insecticide choice is determined by type of insect pest, the severity and duration of the infestation, the regulatory status of the candidate insecticide (is it registered to control this insect pest?), restrictions involved with applying the insecticide, demonstrated efficacy of the product, cost and availability, ease of handling and application, and the need for technical support by the supplier and or the local distributor.

If the treatment area is publicly owned, other factors (public access, other uses, political issues) can often be an important part of the decision-making process.

In the forest environment, very few broad spectrum chemical insecticides are still registered and used. Products of choice include biological products (Bt, virus), semio-chemicals (pheromones) insect growth regulators (IGRs).

Most forest lepidopteran pests are controlled with biological insecticides such as Foray (Btk) or IGR compounds like Mimic.

Choice of Aircraft

The selection of aircraft type and number required to conduct a forest protection program is reflective of several factors:

Size, location and topography of the treatment area: Small spray blocks are most easily treated with smaller aircraft due to their slower speed and smaller payload; conversely larger aircraft can treat a larger area more quickly and can usually treat a larger area per unit time as they have a larger insecticide tank or hopper and they usually have a higher fuel capacity so that the aircraft can carry more insecticide and fuel so they do not have to reload and refuel as frequently. This allows for longer missions and more efficient use of the available time for spraying.

Timeframe Available to Conduct Treatment: Program managers need to know approximately how many days that the target insect will be available and exposed for treatment. For example, many lepidopteran larvae are hidden by foliage for the earliest part of their lifecycle, reducing the timeframe available for control with some insecticides. Some IGR’s can provide some efficacy if applied to host foliage very early, but most Btk compounds require that the pests be exposed and actively feeding on the developing foliage to obtain acceptable levels of control.

In any given treatment timeframe, there are factors which limit the number of hours available to conduct the aerial applications. Local daily weather conditions (see relevant section below), distance to and location of the treatment blocks, flight restrictions due to ground or aerial traffic congestion, access to the treatment blocks are all considerations in program design and aircraft choice

For example, aerial application to forested residential areas may be subject to local ordinances and time restrictions due to vehicular traffic, the presence of pedestrians and bystanders, etc.

If the program requires that staff be present in every treatment block for monitoring purposes, mountainous terrain with difficult vehicular access may preclude aerial treatments in the evenings or even early in the morning.

Availability of Airports or Landing Zones: Modern aerial application aircraft require safe and secure access to suitable airstrips or landing zones. Modern high speed turbine powered airplanes require hard surfaced runways, approximately 3500-400 feet in length. Service vehicles include fuel trucks, insecticide delivery and aircraft loading/refuelling trucks and handling equipment need hard surfaces and secure locations.

Helicopters can be located closer to the treatment area, but they need a suitably large and safe landing zone with good vehicular access, no dust and limited public access for safety and security purposes.

Insecticide Rate and Volume: The type of insecticide and the total volume to be applied are important factors in considering aircraft type and numbers required. Higher volume applications, such as 1.0 to 2.0 gals per acre (10-20 L/ha.) will require larger aircraft or a larger number of smaller aircraft. These insecticide formulations usually require large volumes of water for mixing and dilution, so proximity to al large supply of clean supply water is required.

More highly concentrated insecticides that can be efficiently applied at low and ultra low volumes (less than 1.0 gpa 10 L/ha) can reduce the number of aircraft required with a resultant decrease in the number of support vehicles and personnel as well as reductions in water and fuel supplies.

Cost and Availability: In general airplanes are the most cost effective method of applying an insecticide but access to a suitable hard-surfaced airport and ancillary support services are mandatory. Economies of scale often dictate that larger airplanes may be less costly that smaller ones, but that is not necessarily true. The aerial application industry is very competitive and smaller older (but equally effective) aircraft can provide very reasonable costs.

Helicopters tend to cost more per unit area treated than airplanes, but this can be offset by reduction in program staff required and ease of access to the treatment area.

One of the biggest factors in determining aircraft costs is the layout of the treatment area. A large number of small irregular shaped ‘spray blocks’ scattered over a large geographic area will escalate the costs of protection regardless of aircraft type. Situations like this may preclude the use of cost-effective larger faster turbine powered airplanes.

There are computer models which can be used to help determine insect development, application (spray) timing, aircraft choice and performance, spray block treatment configuration, as well as potential spray deposit and drift. These models should be consulted early in the planning process to help define aircraft choice and to provide advice to program managers.

Airplanes vs. Helicopters: Both types of aircraft are efficient and effective application platforms. Airplanes tend to be larger and faster, so they can provide a lower cost of application per unit area. They require a suitable airport and ancillary services. In remote areas, airplanes are often the best choice as they can ferry long distances safely and effectively. Larger treatment blocks with regular ‘straight line’ boundaries allow an airplane to be most cost effective and maximize spray deposit in the treatment area.

Helicopters are slower speed aircraft and more maneuverable, so they can treat irregularly shaped spray block more easily. They should be located adjacent to or within the treatment area, so that they can make more efficient use of the time available for spraying. Airports are not needed but good vehicle access and a suitable landing zone are required.

Helicopters do not provide better spray deposition than an airplane; once a helicopter is flying at its operational speed, the ‘hover effect’ on spray deposition is negated. Helicopters offer distinct operational advantages, but increased spray deposition is not a factor.

Experience of Program Managers: Both types of aircraft require different support and logistics. Large spray blocks in flat terrain are usually most cost effectively treated by airplanes. Mountainous terrain is often best treated by helicopters due to the size and irregular shapes of the spray blocks in the treatment areas.

Program managers may have more experience with one type of application platform and consequently they are more comfortable with that particular type of aircraft. Program logistics will be organized to reflect their experiences.

Aircraft Application and Guidance Equipment

Modern aerial application aircraft have similar spray systems consisting of an internal or external tank (or tanks), a pump, metering device, a boom and nozzles. The attached schematic covers these components.

The spray tank or hopper may be an integral part of the aircraft’s structure, such as the reservoir included in a purpose-built airplane like an Air Tractor Aircraft. Other fixed wing aircraft may have an externally mounted belly tank that may be a permanent or semi-permanent addition to the aircraft.

All helicopters are converted from other uses and adapted for aerial application. Spray tanks for helicopters may be internally mounted, such as those found in large Bell 205/212 type helicopters. There are several side or belly mount configurations commonly used in smaller helicopters such as the Bell 206, Hiller 12 E, and Aerospatiale etc. In some cases, the spray tank , complete with a power source, is slung on a long cable beneath the helicopter, thereby allowing the application equipment to be quickly attached or detached so that the aircraft may quickly return to other uses.

Spray pumps are controlled by the pilot and they may be powered electrically, hydraulically, or by a separate gasoline engine. The most common configuration, especially with airplanes, is a pump powered by the airstream. The pump is fitted with a propeller blade and is controlled by the pilot to achieve the desired output.

To ensure cleanliness of the spray system, an inline filter is mounted downstream of the pump and before the atomizers. This will ensure that no debris will plug the atomizers.

The spray booms are designed and constructed to withstand high G forces, chemically resistant, and to be easy to mount and dismount They are fabricated in a variety of different cross section profiles, some even acting as a small wing to decrease drag and increase lift.

The spray volume is controlled by a metering device which is now commonly linked to the airborne GPS (Global Positioning System) that most spraycraft rely upon for guidance. These are usually internally mounted turbines and transducers that are calibrated to provide and maintain the required volume to be applied. Modern units are linked to the aircraft’s GPS, and respond to true ground speed, increasing output as the aircraft accelerates, and decreasing output as the aircraft slows down, such as when climbing an incline. This ensures that a constant rate of application is maintained.

The spray is emitted by a series of atomizers installed on the spray boom. The nozzles provide certain characteristics to the spray and atomize the spray material into various sized droplets. Atomizers may produce droplets via hydraulic pressure through a small orifice, or by emitting the insecticide through a rotating device that atomizes the liquid into consistently sized droplets. These later devices are referred to as rotary atomizers or Controlled Droplet Atomizers (CDA’s). Over the years there have been numerous manufacturers providing various styles of CDA’s, however, for forestry purposes, the most consistent and effective spray droplet spectra have been produced by aircraft equipped with Beecomist® or Micronair® rotary atomizers.

Equipment Calibration & Characterization

Care must be taken to ensure that the correct dose and volume are applied; this information is included on the pesticide label.

Calibration ensures that the correct volume of material is emitted from the aircraft and that the correct dosage is applied to the forest. Adjustments are made to increase or decrease flow rates of the pesticide in accordance with the speed of the aircraft and the swath width produced. Swath width is the span or lateral distance that the spray material falls when released from the aircraft.

Characterization refers to adjustments made to the application equipment (nozzles etc.) in order to alter the physical characteristics of the emitted material. Changes will alter the number and size of the droplets produced, how widely it is distributed below the aircraft (swath width) and ultimately how effective your application will be.

There are several formulae used to determine aircraft output. Once it has been determined how many acres (ha.) the aircraft is covering per minute (speed X swath width/495 = acres/min) you can determine the total volume required to treat this area (as per the label) and make mechanical adjustments to apply the prescribed volume. If working in metric, an easy calibration formula is: (swath width (m) X speed (kph)/600) = ha/min.

Next, determine the output per nozzle (total volume/no. of nozzles= output per nozzle) and make adjustments accordingly to achieve the desired application volume.

Once the correct volume has been established, the nozzles may be adjusted to produce a different droplet spectrum, altering the number and size of droplets produced without changing the total volume applied.

Droplet Formation: There are several methods used to produce insecticide spray droplets. Conventional agricultural type ‘hydraulic’ nozzles force the liquid through a small orifice in the nozzle body. The number and size of droplets can be adjusted by changing pressure and flow, or by changing the tip inserted into the nozzle; it is this orifice that determines the atomization characteristics. Changing the type of orifice or its angle with respect to the aircraft’s direction of travel will alter the number and size of the droplets produced.

Other methods include the use of spinning devices that move the liquid under pressure through rotating screens which ‘chop’ the liquid into droplets, all of a similar size. Droplet number and sizes are adjusted by altering the rotation speed of the device; the faster the rotational speed, the smaller the average size of the droplets produced.

In general, insecticide sprays are ideally comprised of a large number of small droplets which allows more spray to be deposited throughout the forest canopy.

Spray Deposit: Once the insecticide has been atomized to provide the desired droplet spectrum (the total number and size of droplets produced) the larger challenge is now ensuring that the droplets produced are deposited at the target sites: the foliage of the host trees in the treatment areas.

Very large droplets are inefficient and often do not provide enough coverage through the forest canopy to ensure contact by the target pests. Smaller droplets are more efficient and provide more coverage, and better canopy penetration, but as they are smaller in diameter, and lighter in weight, they are more prone to off target movement.

Program managers and applicators must be vigilant to ensure that the proper droplet size range is produced and deposited in the target area while off target movement (spray drift) is minimized. Wind speed and direction, temperature and relative humidity are all critical factors to consider in maximizing spray deposition. Some insecticide formulations are more prone to evaporation or wash off, and may require the use of anti-evaporant additives and sticker/spreaders to optimize efficacy.

Spray Deposit Measurement & Monitoring: There are a variety of methods to confirm swath width, spray volume, droplet size and number, and deposition. Tracer dyes, water and/or oil sensitive papers, or sophisticated image analysis equipment can be used. Confirming swath width may be conducted by simply laying out a roll of adding machine tape and have the aircraft make a pass at operational height. This will also give you an initial impression of the droplet spectrum produced.

Unique to Valent BioSciences’ forestry Btk formulations is an ELISA based technology that is used to provide a qualitative assessment of foliar spray deposit. Using the ADAM (Accurate Deposit Assessment Methodology) Kit, representative foliage samples are taken from the treated areas, and processed in the field to determine if adequate deposits of Btk can be found on the foliage. This is helpful in the case of unforeseen post–spray rain events.

These methodologies are further detailed in our Forestry Technical Manual.

Pesticide Formulations

Most Btk based insecticides used in forest protection programs are often fully formulated and can be applied undiluted. In some instances, dilution with water may be required to increase the total volume applied; this does not increase the rate of the insecticide, just the total volume applied, usually in an effort to improve deposition.

Some Btk formulations are composed of a complex wettable granule that is easily miscible with water; it has a longer shelf life than water based products and it can be easily diluted with water to provide a wide range of application rates and volumes.

Formulations are designed with several criteria in mind including cost of production, ease of handling, shelf life, physical characteristics, spray deposit, efficacy as well as environmental and ecological concerns. Some of our products have been formulated to ensure acceptance for use in Certified Organic production.

Handling & Mixing

Pesticides must be stored, handled and mixed properly. Pesticide storage, even for a short term application program, must be in accordance with local regulations. Containers must be secured with access restricted to authorized program staff. Handling and pumping equipment must be checked for leaks and integrity of all connectors in advance of the program.

Most modern insecticide formulations have been developed as water soluble concentrates, produced in either a liquid or a dry granular format. Many applicators have traditionally fabricated their own equipment for measuring, pumping, mixing, and loading spray mixtures into their aircraft. In more recent times, commercial fabricators have built specialized equipment to do this safely and efficiently. Commercial equipment is often designed to meter and mix pesticide solutions quickly and safely. Most units will also rinse and render unusable small 2.5 and 5 gallon (10 and 20 litre) pesticide containers.

Care must be taken to ensure that the right amount of pesticide is mixed and that there are no leaks or spills. Operators must ensure that the proper person protective gear (goggles, gloves etc.) is worn and that all connections are secure and leak-proof.


Weather conditions must be closely monitored to ensure that the applications are made during meteorological conditions that are best suited to maximize spray deposit in the treatment area and to minimize off target movement of the spray. Foliage must not be too wet prior to application (for example, by early morning dew), otherwise the spray may be diluted and even run off the surface of the vegetation, reducing efficacy. The spray must also be applied well in advance of any rain events to ensure adequate time for the spray deposit to dry. This will vary with formulation and weather conditions at the time of spray; labels and manufacturers technical information should be consulted for product-specific recommendations.

Please consult the Forestry Technical Manual for detailed information concerning meteorological conditions and application parameters for VBC forestry products.

Post Spray Assessment

Program managers rely upon a variety of tools to help assess the success of their treatment programs. Initial post-spray assessments are focused upon a review of the DGPS flight files to ensure that the treatment area was completely and correctly flown over.

Spray cards may be reviewed and droplets counted in an effort to quantify the spray deposition within the treatment area.

Program success may be defined through measurements of defoliation, the amount of foliage saved, reduction in target insect populations attributable to the spray, and potential future population levels as predicted by a reduction in egg masses, again attributable to the treatment.

Application Safety

Aerial application programs involve exposure to pesticides and high powered aircraft, working long days with very early morning starts, fatigue and stress. Additionally, for many program employees, these forest protection programs are short term events and often little training is provided to them in terms of duties, responsibilities and management needs.

Appropriate pre-program training is required for all employees, especially with respect to personal safety and potential risks. Often forest fire management organizations offer appropriate training for program staff involved with aerial forest insect control programs.

Aviation hazards include towers, electrical or tower support wires, low level flights at high speed, irregular terrain, and possibly in close proximity to other aircraft. Pilots must be experienced and vigilant; potential flight hazards should be highlighted on all maps and mandatory reconnaissance flights over all treatment areas, prior to spraying, should be instituted.

The safety and security of a forest protection program is of paramount importance and always outweighs the benefits of good results and insecticide efficacy.