United Kingdom

Our two lilac trees have flourished for 30 years and more, but suddenly this year the blooms on one tree were dramatically down: three instead of the usual fifty or more. We had noticed that, from spring onwards, fat pigeons had suddenly taken to perching precariously on the branches and twigs and eating the leaves, a phenomenon we had never seen before. Could there have been an unusual infestation of tasty mites on the leaves? Nothing was visible to explain the strange behaviour.

What might be the explanation, and what action should we take to ensure it doesn't happen again next year?

• 6 Sep, 2015