Greater controls are needed on tree imports to stop new diseases devastating the UK's woods, Kew arboretum head Tony Kirkham has said.
Ash dieback was brought in on German imports to a UK nursery that went out by mail order to 90 gardeners (HW, 8 June). Kirkham insisted that such movement must end: "We have to stop trees going straight into the landscape - that's the key to biosecurity.
"I bring in trees from Germany but they are grown on in a nursery for a year and any problems can be sorted out there. We have to introduce something like that."
He added: "The key is in not letting them in. Prevention is better than control, but you have to have everything ready so you can sort it if necessary."
Kirkham said this year's rain has led to an improvement in tree health despite the influx of foreign pests and diseases.
"We've had so many dry springs and summers that everyone has forgotten what a rainy year is like. In the past 10 years, we have struggled for tree growth. This year is fantastic for growing trees. I love rain because it takes off a lot of the pressure. Our trees are healthier and growth has been phenomenal."
However, he cautioned: "We need some summer heat otherwise lush growth might suffer in early frosts. And I expect second flushes too."
Oaks, cedars and sweet chestnuts are among the trees that have suffered from summer branch drop because of too much growth, he added.
Meanwhile, horse chestnut leaf miner was later this year because of the colder April and oak processionary moth (OPM) had been "knocked back" for the same reason, said Kirkham.
The Food & Environment Research Agency is using the lessons learnt from OPM outbreaks on Asian longhorn beetle, found living in the UK for the first time, he added.
Tree pest alert
Tony Kirkham lists five to watch:
- Emerald ash borer
- Asian longhorn beetle
- Pine processionary moth
- Citrus longhorn beetle
- Bronze birch borer