Detailed Information on Aerial Spraying
Btk for Gypsy Moth
Eradication in
British Columbia
|
 |
|
|
The aerial application of Btk has been determined to be the safest and most effective
method of eradicating populations of gypsy moth in forested, semi-rural and urban areas.
Gypsy moth larvae feed throughout the canopy of trees. To kill the caterpillars, Btk must
be applied to foliage (needles and leaves) and then be eaten by gypsy moth larvae. Trees
come in many shapes and sizes and are located in all types of locations and terrain. Some
of these locations may be very difficult to access from the ground. Aerial application of
Btk is the most effective and cost-efficient method of applying Btk over a large area and
reach foliage located in poorly accessible locations. Furthermore, and most importantly,
over 30 years of aerial application on human populations have revealed no short or
long-term adverse effects to human or environmental health. Btk (including the
formulation Foray 48B that is applied to eradicate gypsy moth in B.C.) is an extremely
safe biological insecticide.
Click here for a description of the advantages
and disadvantages of aerial spraying
 |
Btk is applied as a commercial formulation called Foray 48B (Valent
Biosciences Inc.). For more information on Btk, go the Btk Facts
page. Undiluted Foray 48B is transferred directly from its shipping container into the
holding tanks of the spray aircraft. Aircraft then fly to the site and apply the
insecticide.
The actual dispersal of the Foray 48B is done by a sophisticated arrangement of nozzles
(the figure above shows the nozzles on the trailing edge of the aircraft's wing) that
break the liquid product into the desired droplet size. Droplet size is critical to
maximize the coverage and spread of the product through the canopies of trees. The
aircraft go through a rigorous calibration process using the product before being applied
on the target area. This calibration ensures that the target area receives the desired
droplet size and dispersal pattern.
The aircraft will fly low over the spray zone at an average altitude of 100 feet (30 m)
(Aztecs) to 200 feet (60 m) (DC-6B's) above ground. This height allows the best dispersal
of the droplets and minimizes drift. Aircraft noise during the early morning application
window will be noticeable but the disturbance should be limited to a short time. Each
application per spray zone should be complete within about one and a half hours from
sunrise to about 7:30 a.m. Three applications are
planned for each zone. Each spray will be spaced approximately 7 to 10 days apart although this
interval may vary depending on insect development rates and weather conditions.
Carrying out a successful aerial spraying operation is dependent on several things. A
brief description of some of the most important factors and activities is provided to help
explain how an aerial spray operation is conducted.
|
|
|
|
Aerial application of Btk can be done using various types of fixed wing aircraft or
helicopters. The selection of aircraft depends on the size of the application area,
application window, budgets and terrain. The objective is to use aircraft that apply the
insecticide in the safest and most efficient manner.
Fixed wing aircraft are used when there are large, continuous areas that may be sprayed
with the minimum number of turns. Helicopters are useful for treating discrete or isolated
patches of host material. Fixed wing treatment is less costly than by helicopter.
Aircraft used for spraying can vary considerably in size and configuration ranging from
four engine DC-6Bs to single engine crop dusting aircraft. There is also a similar range
for helicopters. It is up to the project management team to select the right type of
machine for each situation. For example, the 1999 aerial spray project utilized two
types of fixed wing aircraft to conduct the spraying. The larger areas
were sprayed by two DC-6Bs. The remaining smaller areas were treated using a smaller twin
engine Piper Aztec. In all spray areas, aircraft and public safety
are paramount therefore all aircraft are multi-engined.
Monitoring of the spray operation will be done by project team members from both the
ground and the air. Airborne observers will be using small twin-engine aircraft or
helicopters. These personnel relay on-site information back to the project team leaders
and the pilots to ensure that the spray is carried out as planned.
|
|
|
Preparatory Activities Leading Up to the Spray
The Project Team is well-aware of the concerns an aerial spray operation can create
over urban areas and is committed to providing as much information as possible to the
public on the timing and location of all spray activities. Notices of spraying will be
given no more than 24 hours before a spray is planned through radio, television and
newspaper announcements. In addition, an up-to-date web page and listserver
notices will be maintained on the
Ministry of Forests and Range's Gypsy Moth web site to provide the most current information.
|
|
|
|
The weather is the most crucial factor in determining if a spray will occur on a
particular day. Successful control of gypsy moth using Btk requires at least
1 hour
without precipitation to allow the insecticide to adequately dry and stick to foliage that
will be consumed by the caterpillars. If it does rain during this period, some of the Btk
will be harmlessly washed away into the soil out of reach of the gypsy moth.
Wind speed is also a critical factor to the actual delivery of the spray from aircraft.
The morning is usually the most calm period of the day, however, spraying can be done with
some wind. Application is halted when sustained wind speeds exceed 10 km/hr to prevent
unnecessary drift of the Btk. Specific weather conditions are required to allow the
delivery of the insecticide at the desired concentration.
Monitoring of weather will be done using the Environment Canada weather network
supplemented by ground weather stations to give site-specific weather data.
Because of the uncertainty of weather, planned aerial spraying for any particular day
may be cancelled at the last minute.
|
|
|
|
Aircraft apply insecticides in a series of parallel swaths over a spray zone. A swath for
a DC-6B is 720 feet (221 m) while the Piper Aztec has a swath width of 110 feet (34 m).
Well before spraying actually occurs, the route and pattern taken by the spray aircraft
will be determined to ensure that the shortest time is spent over the spray zones. Optimal
patterns will be designed to minimize the number of times the aircraft has to turn. Each
turn wastes time in re-orienting the aircraft as it lines up for its run through the zone.
Safety considerations also play a large role in determining the aircraft's flight
pattern. For example, the very large 1999 Victoria spray block (illustrated above) was split into
four sections with each aircraft spraying one section on one day with an unsprayed block
between them to keep the two aircraft safely separated. The following day (or the next
suitable day), they treated the unsprayed sections, again maintaining a significant
distance between the two aircraft at all times.
|
|
|
|
Spray aircraft use sophisticated Global Positioning System-based navigational aids to
pin-point their precise location. Before these tools were available, the exact location of
spray boundaries had to be set out using helium filled balloons to visually guide the
pilot. These balloons were set up before day-break by ground crews working at each spray
zone. Balloons are no longer used. The GPS
system also provides a record of the exact time and location the aircraft were over the
spray area and also records the precise moment when the spray equipment was on or off. |
|
|
|
Even though spray equipment onboard the aircraft are calibrated well before the time of
spraying, ground monitoring of spray pattern and deposits are done to ensure that the Btk
was delivered to the target foliage at the desired concentration and distribution. Deposit
monitoring is also done to insure that the application does not drift beyond the spray
boundaries. Even application is critical to the performance of most herbicides and
insecticides, including Btk. Uneven application results in under-dosing and poor control
of the target pest in some areas and over-dosing and wasted pesticide in other areas.
Spray deposit monitoring is done using special white coated
KromeKoteŽ cards that are laid out just prior to the spray. Droplets that land on the card's surface are readily
counted. Project specialists can then determine if the spray was carried out as planned.
The majority of droplets will range in diameter from 110 to 125 microns (one
micron=.001 mm) and will have settled to the ground and onto target vegetation about 10
minutes after application.
Gypsy
Moth Homepage > Management Options
> Description of the Eradication Strategy
> monitoring > Selecting
a Treatment > Aerial Spraying with Btk >
Detailed Information on Aerial Spraying > Ground
Spraying > Alternative Treatments
> public involvement
Contact Tim Ebata
if you have comments on the presentation of this information.
BC Ministry of Forests and Range
Forest Practices Branch
P.O. Box 9513 Stn. Prov. Gov.
Victoria, BC
V8W 9C2
Section phone: (250) 387-8739
Section fax: (250) 387-2136
|
|
