The surprising secrets of pears and junipers

A genus-jumping, horny orange fungus plagues a pear tree; dealing with the creepy-crawlies that love fruit just as much as we do

Pear tree rust fungusJennifer has a 'Conference' pear tree growing on a wall in her garden and it is, for the most part, a fine-looking tree, but it's been having problems.

Three years ago the leaves started showing small orange spots which developed horn-like growths on the underside of the leaf.

This is the pear rust fungus, Gymnosporangium sabinae, and it is becoming more common through out the UK. Since the fruit is grown to be eaten, there are currently no fungicides available so we'll need to try and interrupt the life cycle of the fungus.

The RHS doesn't recommend removing affected leaves while they are still on the tree, or the tree may be weakened by being unable to photosynthesise sufficiently, so I've been attending to rigorous plant hygiene and clearing away every single fallen leaf I see. There are still some orange-spotted leaves, but they are much reduced from previous years. 

Orange spot fungus has two hosts, a deciduous one for the period when the tree is in leaf and an evergreen one for winter. The spring and summer host is the pear tree and its winter host is juniper. There is a large Juniperus horizontalis in the garden next door, so it makes sense to examine it and see if there are any stem infections or horn-like outgrowths. If there are, then good hygiene is once again important and those stems should be removed. 

Distorted pear fruitWhat next for this pear tree? This year, for the first time, we noticed that the young fruits were turning black and falling off. What promised to be a good crop is now reduced to a mere dozen fruits. Disheartening but not insurmountable.

The culprit here is a tiny insect, the pear midge (Contarinia pyrivora) which lays its eggs in the pear blossom shortly before opening. Here the larvae form and destroy the developing fruit, which then falls, allowing the larvae to burrow down the pupate in the soil below the tree. If not dealt with, the cycle will continue every year. 

Gently does it

The tree could have been sprayed with a suitable pesticide just before the blossoms opened, but they weren't, so I need to do something else to interrupt the cycle. Once again, I turn to good plant hygiene, removing every deformed pear from the tree and picking up any that have dropped. Working a hoe around the base of the tree should help to disturb any larvae which have made their way into the soil and so prevent their development. 

Non-chemical control takes longer than just spraying, but I do not accept that speed always equals efficiency. By taking the time to clear away damaged fruit and leaves, beneficial insects are not harmed by spraying, the soil is tended and I am able to spot other issues before they cause a problem

'Other issues' are often seen in the form of weeds that may establish themselves while no one is looking. I know someone who swears by cutting back sage with a hedge trimmer, thinking the speed of the job is paramount, but this misses the vast number of rosebay willowherb and thistle seeds that germinate under the plants every year. The hedge trimmer doesn't touch them but, when pruning by hand, they can be spotted and removed at the same time as cutting back the sage. Working by hand may take longer, but in the long term I find it preferable to rushing the job and missing other concerns

Please note, the contents of this blog reflect the views of its author, which are not necessarily those of the RHS

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