It has been so beautiful for years, and then last year the leaves started falling off. I have sprayed with Malathion and dormant oil, but they didn t work. It is about twenty feet tall. It has several dead limbs on it. Pyracantha tends to be plagued with spider mites, and your plant appears to have had a good case of them.
Spider mites like a hot, sunny area, the same as pyracanthas.
The damage that has been done to the leaves, is not going to go away, but new foliage should take its place in the spring. To help rejuvenate these plants, prune them back by one third before new growth begins. Prune out any dead wood. Lightly fertilize them as new growth begins. Watch for signs of damage this season.