Why do my pear leaves have bright orange spots?

This rust has two hosts and cannot complete its cycle without both. It overwinters in juniper stems, releases spores in spring that infect pears, produces the orange leaf spots through summer, and then sends spores back to juniper in autumn. Its spread through UK gardens over the past twenty years tracks the popularity of juniper in planting schemes, and its control is unusually dependent on what your neighbours grow.

Step by step

1. Confirm it is rust and not something else.Bright orange to red spots, a few millimetres across, on the upper surface of pear leaves from about June. Later, brown or greyish warty outgrowths appear on the corresponding spot on the underside. Occasionally the fruit and young shoots are affected too.
2. Look for junipers.Check your own garden and, discreetly, the ones nearby. Infected juniper shows swollen, cracked stems that ooze a bright orange jelly in wet spring weather. That is the source.
3. Remove infected juniper stems if the plant is yours.Cut out swollen and cankered stems well below the damage, or remove the plant entirely if it is heavily affected. This is the only measure that reduces the source of infection.
4. Pick off badly affected pear leaves.Worth doing on a small or trained tree with light infection. On a large tree with hundreds of affected leaves it is not practical and not necessary.
5. Rake up and remove fallen pear leaves in autumn.Standard orchard hygiene. It helps a little with rust and considerably with scab, so it is worth doing anyway.
6. Keep the tree growing well.A vigorous well-fed, well-watered tree tolerates rust with little effect on cropping. Feeding potash in late winter, mulching and watering in drought all matter more than any treatment.
7. Accept it if the source is out of reach.If the junipers are in a neighbouring garden or a nearby landscape planting, the tree will get rust every year. In most gardens it remains cosmetic.
8. Consider replacement only if the tree is badly weakened.Repeated heavy infection over many years with early leaf fall and poor growth is a real problem. It is uncommon, and it is worth ruling out drought, canker and scab before blaming rust.

Tips

• There is no resistant pear variety that reliably escapes it, so replanting a different pear will not solve it.
• If you are choosing new shrubs and have a pear, avoiding juniper is a sensible, cheap precaution.
• The orange spots look alarming and are genuinely striking. Cropping is usually unaffected in a garden tree with moderate infection.
• Rust on the fruit itself is uncommon; where it happens, the fruit is edible but blemished.

Common mistakes

• Stripping most of the leaves off an infected tree — You remove the leaf area the tree needs to ripen its crop and build reserves, which does more harm than the rust does.
• Spraying repeatedly for a cosmetic problem — Garden fungicides are of limited effect against rust on a large tree, and the disease rarely justifies the effort. Fix the juniper source instead if you can.
• Assuming it will spread to apples — European pear rust is specific to pear and juniper. Apples are unaffected.

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