This week at the allotment I noticed the Pear Tree had bright orange spots on the leaves. I had never seen anything like it before so I took a couple of affected leaves home and did some research.
The best website by far for researching garden pests and plant diseases is The Royal Horticultural Society; you can always trust their advice.
What I found out is that my Pear has European Pear Rust which is a fungal disease affecting Pears and Junipers.
The bright orange spots on the leaves are caused by a rust fungus called Gymnosporangium sabinae and tend to appear on the upper surface of the leaves during summer and into early autumn.
What surprised me most about this disease is that you need both pear and juniper for the disease to appear and as far as I am aware there are no junipers at the allotment. However, I am going to have a good look around just to make sure then I will treat both plants.
The rust feeds off the cells of the pear tree whilst it is in leaf but as it cannot survive on dead or dormant plants it will pass the spores on to the perennial juniper, passing back to the pear when it is once again in leaf.
On the pear the bright orange spots on the leaves progress to brown growths on the lower surface of the leaf, the fruit is usually not affected but the stems can get affected causing perennial cankers.
On the junipers the rust causes orange, horn-like swellings on the branches and stems during spring.
The best way to control Pear Rust is to remove the infected pear leaves as soon as you see the bright orange spots; this will reduce the number of spores produced on the pear. If you do see any cankers on the stems of the pear prunes these out too.
To break the cycle you should remove all infections from the stems of the juniper or cut out affected stems; better still move the juniper away from the pear tree or remove it altogether.
It is important not to compost the infected leaved or stems as you could spread the infection around.
For chemical control you can use the fungicide difenoconazole which is widely available as Westland Plant Rescue Fungus Control concentrate.