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12 October 1999
What is Decis Forte (deltamethrin)?
Decis Forte is the trade name of an insecticide known as deltamethrin, which is a third
generation synthetic pyrethroid insecticide approved for use in New Zealand and in many
other countries including USA, UK, Europe and Australia.
Is it safe?
Despite its widespread use, there have been no reports of deltamethrin causing
significant problems. Accidental exposure to the concentrated product at very high levels,
has been occasionally reported to cause skin numbness or tingling but no known long term
effects. No such reports have been recorded from exposure to the diluted spray mix.
What is deltamethrin normally used for?
This insecticide has been widely used by horticulturalists (particularly on vegetable
crops) for about fifteen years. It is commonly used to treat a range of vegetable crops,
as well as ornamentals, for caterpillars and other insect pests.
It is also a component in certain animal remedies, such as pour-ons used to treat sheep
for lice and ticks, and as a flea control.
Why are you using this particular insecticide?
It was important to find an insecticide which would be effective on this pest, whilst
trying to minimise the possible adverse effects. Decis Forte is as safe to humans and
animals as any of the other effective sprays which could be used, but has the advantage of
being able to be used at extremely low dose rates.
In addition the Pesticides Board has already evaluated the environmental and food
safety of deltamethrin for insect pest control in a number of vegetable crops.
How will the insecticide be applied?
Decis Forte comes in the form of an emulsifiable concentrate, which is diluted with
water before use. In the Mt Wellington situation, this will be applied from the ground to
host trees on the infested properties as well as surfaces of buildings and other equipment
Will this spray kill the moth?
Decis Forte is very effective against caterpillars, but less so during other stages of
the moth's lifecycle (i.e. eggs, pupae, and adult). However, as caterpillars emerge
from their eggs and moths from the pupae, the insects may also be affected. Decis Forte
kills insects by direct contact action and as a stomach poison when treated plants
There may need to be a follow-up treatment to catch any new caterpillars that hatch
after the first treatment. Sprays, such as Bacillus thuringiensis (Bt) and
tebufenozide (Mimic), with different modes of action may still be considered for use
against painted apple moth in the future.
Will you be evacuating the properties while the spraying is done?
MAF does not consider it necessary to evacuate the site as such. However, every effort
will be made to spray at times to minimise people's exposure and cause least
disruption to those working on infested sites (i.e., at weekends and/or early in the
morning) so as to give the spray the greatest chance of working undisturbed.
As a general rule, we are recommending that people should not enter the treated areas
until sprayed surfaces are fully dry (about 3 hours) without wearing shoes and long
sleeved overalls/shirt and trousers, and if there is a need to handle the sprayed trees,
then gloves should also be worn for the first 24 hours.
Deltamethrin applicators will be specifically instructed to ensure fish ponds are not
subject to spray drift.
Why is MAF changing from chlorpyrifos to deltamethrin?
Deltamethrin remains active and therefore effective for longer than chlorpyrifos. MAF
had previously stated that it would investigate the use of alternative sprays which might
be more effective or appropriate.