I am in Toronto and have 2 pear trees that are plagued with rust. Any fruit that begins to develop soon falls off. I spray with dormant oil/sulphur. I was removing infected leaves and being very careful to not let any remain on the ground. Last year about 90% of the leaves were infected. Is there any hope or should the trees be removed? :(
I suspect that what you are seeing is Pear Trellis Rust, which is a plague that entered the province in 2007.
The Ontario Ministry of Agriculture and Rural Affairs (OMAFRA) has an excellent fact sheet on the disease, which you can find here:
Because Pear Trellis Rust alternates between pear trees (its summer host) and junipers (its winter host) this disease will almost certainly continue to cause your pear tree to lose its vigour as it is re-infected every year. As the OMAFRA fact sheet says, some people have tried the treatments used for other fungal diseases, but even if you have no junipers in your immediate area, the spores of this fungus can travel up to 6 km on the wind, so the likelihood of repeat infection is very high. I endured four years of repeat infections until I finally faced the truth and removed my own pear tree. Since your trees already have been infected several times, it is probably time to consider replacing them.