Category: Diseases

Hawthorn-juniper Rust

Posted by shane - January 6, 2015 - Diseases

This is a very common disease of hawthorns and juniper shrubs.  The disease requires two hosts to complete its life cycle, and the symptoms look very different on the two host species.  In the spring, the hawthorn leaves emerge and appear healthy.  Soon after flowering, the rust spots start appearing on the leaves and the […]

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Fire Blight

Posted by shane - January 25, 2011 - Diseases, Insects, Diseases & Other Problems

Fire blight is very common on the Prairies.  Some years are worse than others.  In Calgary and Red Deer, in 2009, it was particularly severe.  Epidemics occur during warm, humid weather, with relative humidity above 60%.  The bacteria responsible for the disease can multiply at temperatures between 15-32C, but do so most readily between 27-29C.  Outbreaks can follow severe storms, […]

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Black Knot Fungus

Posted by shane - January 25, 2011 - Diseases, Insects, Diseases & Other Problems

 Black knot is one of the most commonly encountered diseases among ornamental plantings.  I see it most often on mayday and ‘Schubert’ chokecherry trees.  Besides poor planting techniques and poor plant quality, black knot is the most common cause of plant death among those species. Easily recognizable, black knot starts as swellings on the twigs in […]

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