The minute flat scarlet mite can be quite damaging, particularly if growers are not aware of its presence, and many insecticides don't control it.
"The pest was quite serious in the 1950s and then it disappeared but it has undergone a resurgence since 2005, mainly on Cox," EMR research team leader Dr Jerry Cross told the British Independent Fruit Growers Association's 22nd annual technical day.
"It's now very widespread, particularly in orchards run by growers who don't realise it's there," Cross added. "Changing production patterns could be the reason although typhs do predate it."
Speaking at the event, held at the Bewl Water conference centre near Lamberhust in Kent, he explained that the mite's feeding activity causes scale round the apple's eye and small necrotic patches on the leaves. Its eggs overwinter and hatch in April and early May, which is the time to spray for the most effective control.
But many pesticides including mitochondrial electron transport inhibitors such as Masai and Sequel are ineffective. Talstar does kill it but at a cost to beneficials. The new miticide Envidor seems to be the best choice.
Another apple and pear pest that disappeared for a long period, Mussell scale, has become well-established in recent years in areas such as Kent's lower greensand ridge. Cross said it is quite common on hawthorn — a possible source of the pest for new orchards.
He explained that crawlers emerge from beneath the scales in spring and disperse over the tree, "sometimes in enormous numbers". Some settle on the fruit causing downgrading, others on the trunks and branches and some on the leaves, although "these are doomed to die" after leaf fall.
Double-sided Sellotape wrapped round the tree trunks can be used to monitor the emergence of the crawlers, which get stuck when they try to crawl under the tape. Over the past three years, crawler emergence generally has begun in mid-April and continued for four weeks or so. In each year there was an unaccountable dip in the numbers caught part way through peak emergence.
"We found that a single spray at 90 per cent emergence gave the best results but if there's a big emergence you need two sprays - at 50 per cent and 90 per cent," said Cross. "Sticky tapes are great but who is going to use them?"
He added that the Farm Advisory Services Team had found that the winter application of winter oil plus chlorpyrifos was a good alternative to spring treatment.