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Spray Update
2014 Fall Cankerworm Aerial Suppression Program
On May 5th, the Mosquito and Forest Pest Management Branch completed a program to suppress fall cankerworm populations.  Treatment was accomplished by aerial spraying.  The treatment area was selected based on defoliation surveys conducted last spring and fall cankerworm surveys done this winter.  These surveys indicated that populations are high and defoliation of trees will be severe. 
The program is voluntary and is designed to prevent widespread defoliation and mortality of affected trees. Open fields and open areas with a few scattered trees will not be treated. 
To view a detailed Map that outlines the proposed spray boundaries, click here.  For additional features such as zooming and aerial photography, visit County Mapper XM.
The following information should answer many of your questions. 
WHAT IS THE FALL CANKERWORM? The fall cankerworm  is a serious defoliator of forest and shade trees. This pest, while in the larval stage, damages trees by feeding on the leaves. Trees can be killed by two to three years of defoliation depending on the overall health of the tree.
HOW IS SPRAYING DONE? The treatment will be conducted aerially using a helicopter with Tail #N6344D.  The helicopter will fly very low and loudly over treatment sites and surrounding areas. It will remain in the area until the completion of the day’s spray plans and as long as weather conditions remain favorable. Spraying may last into the late morning or afternoon.
WHEN WILL MY SPRAY BLOCK BE SPRAYED? Treatment depends on weather, leaf development, and egg hatch.  The projected start date for spray is May 5th.  It may take 1-3 days to complete the spray, depending on weather.  Spray will commence around 7am.  You may also check for spray schedules by calling the PWC–INFO line: (703)792-4636, press 4, and then press 1. Treatment usually begins shortly after dawn and continues throughout the day on a daily basis as long as weather conditions permit. Your property may be in the spray block and partially in the buffer zone. This does not mean that any of your property will be treated twice.
WHAT INSECTICIDE WILL BE USED IN SPRAYING? The spray block will be treated with Bacillus thuringiensis kurstaki (Btk),  which is an insecticide registered for use against fall cankerworm by the U.S. Environmental Protection Agency. Btk is a naturally occurring bacterium that causes fall cankerworm caterpillars to stop feeding so they starve to death.  To learn more about Btk, click here and here.
WHAT PRECAUTIONS SHOULD I TAKE? The helicopter will be flying low and will be loud.  Please bring in any pets.  Individuals with severe allergies may wish to stay indoors during spray application and for 30 minutes after the helicopter leaves the area.  Children waiting at bus stops should not be concerned as no spray will be scheduled during pick up hours. 
HOW CAN I GET MORE INFORMATION? You may call our office at (703) 792-6279 or send an email to


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