Tortrix control

[monkeybusiness]

A new customer has asked me to try and sort out her fruit trees (Apple, Damson, Malus) which are being decimated by Tortrix caterpillars for the 3rd year running (I haven't seen the trees previously - I am taking her word for it with regards the historical problem). She reckons that this year's infestation is the worst yet - all emerging blossom and leaves on the group of trees is being instantly destroyed by thousands of caterpillars, and she has had no fruit for the last 2 years.

Aside from letting nature take its course through bird feeding etc, what other course of action is available. My thoughts run with spraying with a pesticide, but what is currently available that will be effective here? The physical pesticide application is not a problem, I just could do with some help/advice on what to use.

Cheers!