Controlling nut scale (Eulecanium tiliae) and mussel scale (Lepidosaphes ulmi) insects on apple trees requires careful timing and application, given the limited control measures available to growers, delegates were told at last week's Bulmers Orchard & Machinery Day.
"You can see trees dying from it," said Agrii fruit agronomist Brian McCarthy. "Fifteen years ago you would use a tar wash to mop up these kinds of pests. Now they are a serious problem and the treatments you have are pretty limited."
He suggested applying Calypso when the immature insects emerge from their scaly shells in summer - for which "you have to examine your trees daily to see if the underside changes from an oatmeal colour to salmon-orange", he explained.
"One treatment should clean it up. But it's better to apply just before pink bud, when the adults are feeding and vulnerable."
Envidor and Insegar can serve as alternative treatments, particularly on varieties such as Michelin that are vulnerable to scorching from Calypso, he added.
As for alternative controls, a naturally occurring Beauveria-like fungus is thought to kill some of the insects and "could be developed in the future", said McCarthy.
An as yet unidentified parasitic insect also appears to predate the pests, but so far it is known only from the exit hole that it leaves in the dead scale insect's shell, he added. However, any deployable treatment of this sort is some way off.
"The chemicals work well as long as the timing and application is correct, so make sure that your sprayer is set correctly to cover the full height of the tree and consider using sensitive paper to check," McCarthy urged.
Bulmers area farms manager Ben Moss said: "Nut scale has affected tree growth here this year in our Dabinett orchard. We have yet to see how it affects fruit size or next year's fruiting."
Penrhos Farm Orchard & Machinery Day
Bulmers hosted the pan-industry Orchard & Machinery Day at its Penrhos Farm in Monmouthshire - its largest site in terms of trees, with more than 95,000 planted over 140ha.
Some blocks of established trees have been regrafted with different varieties. "They are more work but it's an opportunity to take advantage of an established root system," said area farms manager Ben Moss. He put the cost of professional regrafting at £2 a tree.