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New Rust in Town?

By Brad Gurr Created: February 8, 2013 Last Updated: February 8, 2013
Related articles: Science » Earth & Environment
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Leaves with pear trellis rust. (Brad Gurr)

Leaves with pear trellis rust. (Brad Gurr)

For the Bradford pear, its long reign as the most trouble-free tree may have come to an end. Recent laboratory-confirmed cases of pear trellis rust (Gymnosporangium sabinae) have been located in Northeastern United States. While pear trellis rust has been present in Southern Ontario since 2007, and is a common disease in the Pacific Northeast and Europe, it has not been discovered beyond those areas.

Pears, up to this point, have been free from most pests and had only their poor structure to cause problems in the landscape. Like most rusts, pear trellis rust requires two distinct hosts at different times of the year.

The summer host, the pear, is the most disfigured by the rust and may become completely defoliated if the outbreak is severe. Repeated unchecked outbreaks could result in dieback and mortality.

The winter host, the juniper, is much less severely affected. The disease overwinters as a gall on the juniper, erupting in the spring with bright orange gelatinous fruiting structures called telia. These structures produce spores that are carried by wind to the nearest pear. Under ideal conditions, these can travel up to four miles.

The effect of pear trellis rust on landscape trees is dramatic. After the initial infection, which causes reddish-orange blotches on the leaves, the leaves turn brown and will fall from the tree throughout the growing season. On fruit trees, it will destroy a crop in short order. While the life cycle of this disease is complicated, its unsightly effect on pears is simply awful.

All pears appear to be susceptible to varying degrees. Cultural controls, like removing junipers from the area, are not realistic given the close proximity of the two hosts in a typical landscape. Even if you were able to remove your junipers, the possibility of there not being one in the area to act as a secondary host is remote.

As pear trellis rust is a newly discovered disease, treatment plans are still in the developmental stage and no fungicides are currently labeled to control this disease. One suspects that, in time, a treatment regime similar to apple rust will emerge and prove effective in controlling this newfound nemesis of pears.

Take the time to contact your ISA Certified Arborist today and have your pears accessed for the potential impact of pear trellis rust. Panic is pointless; preparation is priceless.

Brad Gurr is an ISA Certified Arborist and Plant Health Care Specialist with SavATree. For more information on this subject or any plant health care-related questions, please feel free to contact him at bgurr@savatree.com

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