Garden diseases - Pear rust

A pear rust infestation is easy to spot
Image: JGade/Shutterstock

If you notice bright orange “rust” spots on your pear tree leaves during the summer and into the beginning of autumn, the chances are you’re dealing with pear rust, a fungal infection that spread to the UK from mainland Europe. Fortunately, its effects are mostly cosmetic, but like any infection, if it gets a real hold on your trees, it will weaken them over time. Here’s how to recognise and deal with Pear rust.

What is pear rust?

Fruiting bodies of pear rust fungi live on the underside of the leaf
Image: Kazakov Maksim/Shutterstock

Pear rust spots are the result of the fungal infection, gymnosporangium sabinae. The spots are bright orange and as they mature, the underside of the leaf develops a bulky growth from which protrude tiny “fingers” – it’s from these that the fungus spreads its spores.

The disease doesn't spread via other pear trees but instead jumps to neighbouring junipers which develop swellings on the stems which then develop into orange horny outgrowths. The junipers harbour the fungus during the winter until the following spring when it hops back to your pear trees.

What to do about pear rust

Pruning out the affected material is the only way to limit the spread of pear rust
Image: Anakumka/Shutterstock

Because there are no fungicides recommended for trees producing fruit you intend to eat, your only option should you notice pear rust, is to prune out affected material. Dispose of it by burning or putting out with the rubbish rather than composting which doesn’t kill the spores. Bear in mind that if you’re dealing with a severe infection, you may do the tree more harm than good by removing all affected material.

One way to reduce the chances of infection is to remove junipers from the area surrounding your pear trees – it’s worth a try, but remember, fungal spores can travel quite a distance on the wind so this is not guaranteed to work.

Overall, though pear rust looks rather dramatic, it doesn’t seem to pose a huge problem – severely affected trees will be less vigorous and produce fewer pears, but acting promptly to prevent and deal with the problem should prevent this. 

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