The fruit on my pear trees is swelling then turning black and shriveling, can you provide a reason and a cure please?

Your pears have been attacked by pear midge.

The midge lays eggs in the flower buds as they start to show white petals and the grubs feed inside the embryo fruit.

The young pears seem to grow quite well for a while then they begin to swell, then turn black and shrivel as you mention.

Next year, control by spraying with a suitable insecticide as the first white petals appear

Remove and burn any fruitlets that appear to be infested.

Follow the same treatment the following year also,and hopefully that should put an end to the infestation.

When is the right time to summer prune cordon pear trees?

Late July, early August is the right time to summer prune trained pear trees.

Cut back side shoots that are growing directly from the main stem, to within three leaves of the basal cluster of leaves.

Shorten the new shoots arising from older spurs to one leaf above the basal rosette.

My pears have started to rot whilst still on the tree, is there any way to prevent this?

The rotting is brown rot fungus, resulting from fruit damage.

The damage is generally caused by bird pecking, or wasps feeding.

The cure is somewhat difficult, particularly on large trees where the fruit is not readily accessible.  

With a small tree, the fruits could be enclosed in ventilated plastic bags or the feet, cut from old tights.

 Proprietary wasp traps can be hung in the trees to try to divert their attention away from the fruit.

Pick off any fruits showing infection and dispose of them.

We had a poor flower set on our pears this year and most of those that did set, became rounded, then turned black and rotted, whilst only thumb­nail size.

What action can we take to avoid this happening again?

Pear midge was responsible for the damage to the pears, and the poor set was probably due to adverse weather at flowering time, and a lack of pollinators.

Control them by spraying the tree at bud stage with a suitable insecticide.

If the pear tree is growing in bare soil, and not in grass, cultivating lightly around the tree may expose the over wintering larvae which in turn may be eaten by birds.