Pear Rust is an increasingly common fungal disease in pear trees. This disease can significantly slow the growth of a pear tree, and the tree will also give less fruits. Pear Rust is a fungus that cannot stay the whole year on the pear: in winter the tree has no leaves and the fungus is only present there. In winter, the fungus needs a Juniper to overwinter. After the winter the fungus makes spores, which are spread through the air. The spores fall on the pear tree, causing the fungal disease.
Pear Rust is very easy to recognize. The disease begins with deep orange spots on the leaf, often with a brown core. These spots are often oval shaped, but not perfectly round. Later under the leaf, a large orange hump is formed on the same place as the spot, later even with light brown to white projections. From there, the fungus spores are spread.
The best way to combat this disease is to remove the Junipers that transmit this disease. If all the Junipers in the area (this can be several hundred meters away) are removed, damaged leaves should be removed and the tree must be plucked bare in winter. If it is not possible to remove the Junipers, the disease can still be kept in check. The most effective method to do this is with a combination of the removal of degraded leaves before the disease further infects the tree, and spraying with a pesticide. The problem with this is that the treatment has to be repeated constantly: for example, spraying has to be done five times a year, depending on the severity of the disease. However the fungus will continue to hide in the Juniper and can just come back.