Pear rust, also known as pear trellis rust, is a fungus spread by wind-blown spores. Both juniper and pear trees suffer from this fungal disease, and they spread it rampantly to each other when the two types of trees are planted close to one another. Pear rust is most common in Europe, on southern Vancouver Island, in one county in California and in one area of Washington State. Rust is difficult to stop, especially if your neighborhood has a lot of junipers and pear trees planted close enough to each other that the spores can spread through the air. There are some preventive measures you can take, however, to stop pear rust.
Determine whether pear rust is indeed your culprit. You should see orange spots covering the leaves in early summer, changing to fuzzy growth in autumn. In mid-summer, the orange spots will develop black spots, and then the spores will produce structures that erupt from the leaves' lower surfaces.
Plant juniper trees as far away from your pear trees as possible. Make sure the junipers and pear trees are at least 100 feet apart, as this will prevent the spread of rust from the junipers to the pears. The rust fungus will over-winter on juniper trees.
Remove the nearby infected junipers in early spring to contain the spread of the fungus and damage to your pear trees. Be sure to remove from your yard all parts of the tree that you've cut down.
Pick off the infected leaves on your pear tree in the spring and early summer every year. This will help to prevent spreading the disease to your neighbors' junipers.
Prune any infected pear trees frequently, cutting out any growths at the base of the twigs. These growths on severely infected pear trees are an unstoppable source of infection in the tree.