I had a 4 year old peach tree in a large pot suddenly in late spring the leaves began to droop. On taking it out of the pot I found a number of small white grubs on the roots. Has anyone any ideas as to what they were and how to prevent a recurrence of the problem?

Did these grubs have orange heads and were they culed up like the letter'C'? If so then they were/are vine weevil grubs. On none edible crops you can use Vine Weevil Killer as a drench, but on edible crops it is a bit of a problem. So first of all, wash the roots bare and repot in clean fresh, none peat based compost. They prefer peat. Then make yourself a plastic lid for the soil (I use the black plastic which is commonly sold for covering soil. Put some small holes in it to allow water through and cover the soil, right up to the stem of the plant. Then cover the whole of it with at least 2 inches of gravel/grit. The adults like to lay their eggs on the soil next to the stem of a plant, so if they cannot reach the soil they tend to go elsewhere.