Then there is oak processionary moth, which causes allergic reactions, first found in neighbouring Richmond and "not yet here but almost certainly coming soon". There are also parakeets, which are now local to south-west London, as well as Phytophthora, squirrels, cankers and budget concerns with which to contend.
You can see very clearly that the leaf miner is ravaging the trees from Lofthouse's 12th floor office window in Morden this autumn. The shot trees are horse chestnuts and the green ones are everything else. The Cameraria ohridella may have come in on NATO vehicles from Kosovo in the 1990s but is more likely to have been imported on cars travelling back from holidays in the Balkans.
Lofthouse, who has been at Merton for 20 years, says modern mobility is to blame. He now plants only Indian Horse Chestnut, Aesculus indica, available in limited numbers, rather than planting the doomed Aesculus hippocastanum.
He points out that the only control method is to collect leaf litter and burn it but councils do not have the resources to do that, although Bushy Park has tried it successfully.
"There's not much we can do other than wait and hope a natural predator will appear and the population develops to more normal levels," he says. He praises the Forestry Commission's work on the oak processionary moth but says the pest needs a joint approach with health authorities.
Lofthouse is the new London Tree Officers Association (LTOA) chairman, having taken over from Oliver Stutter in June this year for a two-year term.
The LTOA includes representatives from almost all London's 33 boroughs. Lofthouse would like that to be 100 per cent again, as in some previous years. LTOA working parties deal with many aspects of tree work. They include projects such as the risk limitation strategy on dealing with subsidence claims by using the CAVAT tree-valuing system and the Joint Mitigation Protocol. A working party is writing a guidance note on oak processionary moth. Lofthouse says: "These things need to be punched out regularly by the LTOA."
Members have expressed interest in a note on closed-circuit television and trees, which has become an issue as tree officers receive more requests to prune to improve fields of view for cameras. Upcoming issues are how to improve tree canopy coverage in London and anything else members suggest - they know what they need.
Lofthouse says the beauty of the LTOA is that it offers arboricultural excellence and good practice guidelines as well as advice on when to do something and how to achieve it so that each tree officer does not have to make an individual response. Using the guidelines means less workload for each officer because they don't have to argue each case on their own and are "not reinventing the wheel all the time".
The former miner began as a tree gang member at Bristol City Council in 1974 before the Health & Safety at Work Act 1974 brought in use of harnesses and ropes, with which Lofthouse had experience.
His decades in council tree work have led him to conclude that, in local government, parks with no litter and mown grass are sometimes seen as more important than having alive, staked, pruned and watered trees. He says bowsers and long hoses are "basic equipment often absent from city parks".
The profile of arboriculture has risen in the past 10 years, he says, because of climate change, biodiversity and the green agenda's raised profile, but that has seldom been reflected in monetary terms.
He adds: "Arboriculture has become more professional. People are worried about professionalism and talk about it a lot, which can make them sound insecure. But it is a young profession. Twenty years ago some councils still didn't have tree officers, but those without a team are in a minority now."
He says in the early days at Bristol he would be given "half-a-dozen locations and told the trees that were scheduled to be pruned and to go and deal with it. There was no specification. You just did what you thought was needed so you might reduce and not thin or fell and not reduce. It was all on scraps of paper."
Lofthouse points out tree work is more sophisticated now, as is collaboration between industry bodies and between boroughs. "The uniqueness of the LTOA is the closeness of all these local government arboriculturists in one huge city full of trees - we share many of the same problems and we are immediate neighbours so we can do things fast," he explains.
1974-86: Tree worker, Bristol City Council
1986-89: National diploma in arboriculture and national certificate in arboriculture, Merrist Wood
1989 to date: Senior tree officer, London Borough of Merton
1999-2000: Chair, LTOA
2010-2012: Chair, LTOA.