Hi, why do the fruit on my nectarine tree shrivel up like prunes before ripening?

Hi Shirley 

This sounds like brown rot, which is a fungal problem.  

Brown rot overwinters in the bark of the tree and wet weather at the time of flowering helps spread the fungus. It is too late now to do anything, other than picking off infected fruit and cleaning up any fallen leaves to stop the spread of the disease. Remove overwintering fungal spores then burn or dispose of in the rubbish.

Spray with a suitable fungicide in late winter early spring before and during bud burst. We suggest checking with your local DIY and Garden Centre for a suitable spray. Make sure the tree is pruned with an open canopy to improve air circulation and reduce conditions fungi love to multiply in. 

Thanks, Tui Team.