I’m happy to say that the main pear tree is looking very healthy. I have been religiously removing leaves at the first sign of the mite, and it has kept it under control. It also has an incredible crop of pears growing – too many for the poor tree, in fact.
One thing I didn’t know was that it is also advised to rub off about half of the flowering buds, before they get a chance to develop fruit at all. The reason for this is that apples and pears can become biennial, with a heavy crop one year, and nothing the following. By thinning out the flowering buds, it encourages the tree to produce new buds for the following year.
Perversely, the dwarf pear I got because the main tree was so unhealthy is now the poorly one. Not the same problem as before, and it doesn’t look as serious as the mite, so I think it is just a case of needing some TLC.