Scout your Bradford pears now for European pear rust

European pear rust has been found in southeastern Michigan this 2014 season.

European pear rust on Bradford pear. All photos Jan Byrne, MSU

European pear rust on Bradford pear. All photos Jan Byrne, MSU

First detected in Farmington, Michigan, in 2008, European pear rust (Gymnosporangium sabinae) has been detected on Bradford pear (Pyrus calleryana) in southeast Michigan this 2014 season. The most severely affected cultivar is the Cleveland pear, which has a narrower growth habit than other pear cultivars. This compact growth habit reduces air circulation and creates a favorable environment for the growth of fungal diseases, such as European pear rust.

European pear rust can infect species of the pear and juniper genera, Pyrus and Juniperus. European pear rust on juniper has not been recorded in Michigan, but is fairly common in Europe. On pear species, the fungus has distinctive orange sporulation on the leaves occurring in the summer and early fall. On juniper, the fungus causes cankers on the stem, which produce an orange gelatinous substance in the spring.

If European pear rust is detected in your nursery or landscape, prune out infected branches or remove the entire tree, depending on the severity of infection. Because the rust often overwinters on junipers, which provides a source of inoculum for the pear trees in the spring, try to inspect nearby junipers for cankers prior to the winter. Michigan State University Extension advises separating pear and juniper species in the nursery to prevent cross-contamination if the disease has been found. 

European pear rust

The above-average precipitation throughout the state during June 2014 is conducive for fungal diseases, such as European pear rust. For example, the Commerce Township Enviro-weather station in southeast Michigan recorded 3.57 inches of rain throughout June, which is slightly above the average of 3.06 inches. On the west side of the state, the Sparta Enviro-weather station received 8.3 inches of rain during June, which is exceedingly high compared to an average of 3.17 inches. Nursery growers or landscape professionals should be scouting all types of plants for fungal diseases now.

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