This year has been active for pear rust development. This disease (Gymnosporangium spp.) requires two host to complete its life cycle — a pear and a juniper. There are several related species of this disease that also cause Cedar Apple Rust, Pear Trellis Rust, Cedar Quince Rust, and others. As you can see in the photo below, orange growth occurs on the leaves and fruit. Later in the summer spores are released and blown by wind to the nearest juniper host. On junipers the disease appears as a gelatinous mass on the branches that eventually hardens to a brownish colored gall.
Photo courtesy of Allan Whitehead, MSU-ES
What to do about this disease? Sanitation is very important. Clean up all infected leaves, fruit, and other plant parts and dispose of them away from the orchard area. Prune out infected tissue on both pears and junipers. Some pears and junipers are resistant to this disease, so choose those varieties if considering a new planting. The only sure way to eliminate the disease is to get rid of one of the hosts — either the pear or the juniper. Approved fungicides may help, but it will be a constant battle and timing of application will be critically important.
Some good links on rust diseases that show more photos and suggestions on control: