It was meant to protect wildlife in Berkshire but there are now fears it's having the opposite effect. Last month, the Forestry Commission sprayed insecticide from a helicopter over Sulham Woods in Pangbourne.
It was meant to kill a toxic caterpillar - the Oak Processionary Moth - but environmental groups say the chemicals have killed too many other insects and it's driving birds, bats and other wildlife away.
Earlier, ITV Meridian's Sangeeta Bhabra spoke to Vanessa Amaral-Rogers from the conservation charity Bug Life and asked her what damage she thinks the aerial spray has done.
In a statement the Forestry Commission "We fully share Buglife's concerns, which is why we have worked with Natural England and others to ensure that the treatment has the leastpossible effect on other wildlife.
"It is too soon to draw conclusions, and our five-year monitoring programme at Herridge's Copse will give us a more accurate picture of the long-term effects.
"The consequences for Britain's woodland wildlife, and for people living around oak trees, of NOT tackling Oak processionary moth would be much more serious."