Swathes of woodland will be sprayed in a bid to eradicate a toxic caterpillar which can cause eye problems and breathing difficulties.
The Forestry Commission will use helicopters to spray a pesticide over one part of England where the oak processionary caterpillar has made its home.
The insects, which usually emerge from eggs in May, are covered in thousands of tiny hairs which release an irritating substance called thaumetopoein.
The hairs are blown about by the wind and cause painful skin rashes in humans and animals.
They can also lead to eye and throat problems in more extreme cases.
Stewart Snape, of the Forestry Commission, said: "Most oak processionary moth treatment is done by spraying individual trees from the ground, but it's much more difficult to find and treat the pest in a woodland environment than in trees in a park or street, with a significant risk that some will be missed.
"The most effective way to treat the woodland is to spray it from a helicopter using an ultra-low-volume spray system. Helicopters can fly lower and slower than fixed-wing aircraft, and therefore target the spray very accurately.
"In addition, the downdraft from a helicopter's rotor helps to achieve much better penetration of the foliage than fixed-wing aircraft or ground spraying can achieve."
The Forestry Commission will use Bacillus thuringiensis - a bacterial agent which occurs naturally in soil - to eliminate the caterpillars from two forests near Pangbourne, Berkshire.
People living nearby have been told the pesticide poses no risk to human or animal health, and experts will monitor birds, bats, moths and butterflies to ensure it does not affect other wildlife species.
The caterpillars invaded Britain in 2006 when young oak trees were imported from mainland Europe.
They have been found in Berkshire, London and as far afield as Leeds and Sheffield, although there is no evidence of any breeding populations outside of the South East.
Dozens of nests were found in Berkshire in 2011, although that number had been reduced to three by last year.