Tuesday 18 September 2012

New Rust in Town

                                 photo TCC

For the Bradford pear the 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 the North Eastern United States . While it has been present in Southern Ontario since 2007 and  is a common disease in the Pacific North East 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 out breaks could result in die back and mortality. The winter host, the juniper, is much less severely affected. The disease over winters as a gall on the juniper erupting in the spring with bright orange gelatinous fruiting structures called telia. These structures produce spores that are blow in the wind to the nearest pear. Under ideal conditions these can travel up to four miles.  The effect on landscape trees is dramatic. After the initial infection causing reddish orange blotches on the leaves the leaves turn brown they will fall from the tree throughout the growing season. On fruit trees it will damage 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 this 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 new found 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.

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