Advice

European pear rust

Plants affected

Principally pear (Pyrus communis), although there are some records on other Pyrus species. Also Juniperus sabinae and other species in the subgenus Sabina.

Symptoms

On pears, orange spots appear on the upper leaf surface - corresponding to brown growths underneath, and sometimes they also appear on young stems or fruit.

On junipers there are spindle-shaped swellings on the stems, producing a mass of orange spores in the spring.

Cause

The disease is caused by the rust fungus Gymnosporangium sabinae (= G. fuscum), which requires two hosts, pear and juniper, to complete its life cycle. Spores produced from the fungal growths on pears are airborne and infect junipers; spores produced from the fungus-induced swellings on juniper stems are airborne up to 6km and then re-infect pears.

Control

In the UK, this disease was formerly rare, but in recent years has become more frequent and severe. In commercial orchards it is suppressed by fungicides used to control other fungal diseases. For gardeners there are no specifically approved fungicides, but those labelled for pear scab and powdery mildew will similarly give incidental control.

Removal of nearby juniper (or pruning out infected branches) may have some effect in breaking the life cycle, but infection of pears by wind-blown spores from junipers some distance away will still be a risk.