Asked January 21, 2019, 8:32 AM EST
Wayne County Michigan
You need to treat preventively each year, unless you decide to tolerate the rust on the leaves. The wetter the spring, the more rust is likely to develop.
Originally the ornamental pears were considered very disease resistant but now their diseases are showing up. Our wet spring set the stage for Pear Trellis Rust -scientific name Gymnosporangium sabinae , also known as European pear rust, and it was very common in Eastern Michigan in 2017. Fungicides are used to protect the leaves in the spring as the buds begin to swell. Repeat applications through lef expansion are necessary during wet conditions. Once leaves are developed they become less susceptible to the rust.
If our spring is drier this year you should experience less rust:
European pear rust is related to Cedar-apple rust and several other rust diseases where cedar or juniper is one host and and a member of the apple genus (Malus) such as apple, quince or hawthrone, or pear genus (Pyrus), is the other. Treatment is the same. Here is a link to Pear trellis rust management-
If you have junipers close by( within 300 feet) look for the galls. Pruning them off and discarding them or burying them helps reduce the spores in your area. Clean up fallen pear leaves and fruit and seal in bags. Trees can be thinned to help leaves dry more quickly.
Timing fungicide sprays is critical. Thorough coverage is, too. Never spray when bees are present. Always follow the label precautions, application rate and frequency- products have different rates. This link describes some effective fungicides on the last page for Pear Trellis rust management
You may want to try organic options, as noted in the above article. Or not spray anything when spring is predicted to be dry. Thanks for using our service.