Sightings of larvae have already been observed in Kew Gardens and Richmond Park in west London, according to the London Tree Officers Association.
Explaining the approach, Forestry Commission representative said: "We have identified that the most effective use of finite public resources is to concentrate on containing or limiting the spread by looking for and destroying OPM around the perimeter of the outbreak area, in the Control Zone, while we look to our partners to contribute within the Core Zone."
The Core Zone comprises all of the London Boroughs of Richmond Upon Thames and Hammersmith & Fulham, and parts of the London Boroughs of Ealing, Hounslow, Kingston Upon Thames, Merton and Wandsworth, where the commission encourages tree owners and managers to employ best practice to control numbers and minimise public nuisance.
He added: "We have no current plans to treat trees in Pangbourne, Berkshire, after no nests or caterpillars were found there for two consecutive years. However, three adult moths were caught in pheromone traps last year, indicating a continuing presence, so we will continue to monitor the area this year."
Meanwhile a report from Butterfly Conservation, bringing together several studies of sites sprayed with the biological control Bacillus thuringiensis (Bt), has concluded that this has "a significant impact" on non-target moths and butterflies, even a year after spraying.
However it conceded that eveidence for impact on species which feed on moths and their larvae, such as birds and bats, "is less strong".