When bright orange-red spots appear on the leaves of your pear in summer, pear rust is almost always at work. It looks dramatic, but its greatest weakness makes it well manageable: it absolutely needs a second host.
This article is the detail edition to the overview in Recognising fruit tree diseases. Understand the host alternation behind it and you hold the key to getting rid of the rust for good, without spraying once.
How to recognise pear rust
The damage picture is unmistakable. From early summer, bright orange-red, roundish spots appear on the upper leaf side and grow larger over time. At the same spot, warty then grid-like brown outgrowths form on the leaf underside, from which the fungus releases its spores. This grid structure gave the disease its name.
In heavy attack the trees drop leaves and are weakened over the years. The fruit itself is usually not affected. Strikingly, the attack often appears only on one side of the garden, namely where the second host stands nearby.
The trick with the host alternation
Pear rust is a host-alternator. It cannot multiply on the pear alone but absolutely needs a juniper for it, above all the savin (Juniperus sabina) and some ornamental junipers. On the juniper it overwinters and in spring forms conspicuous orange, gelatinous outgrowths.
In spring the spores blow from the juniper to the pear, where they trigger the orange-red spots. In late summer the journey goes back to the juniper. From pear to pear, by contrast, the fungus cannot spread. And that is exactly your point of attack: without juniper in the surroundings, the cycle is broken.
What really helps
Remove the juniper
The only truly effective measure. Remove the savin or susceptible ornamental juniper from your garden. If it stands at the neighbour's, a friendly chat helps, because the savin is also toxic and easy to replace.
Remove affected leaves
Gather heavily affected leaves and dispose of them in the residual waste. That reduces the infection pressure but does not replace removing the juniper.
Keep the crown airy
An airy tree dries quickly and copes better with an attack. How to prune correctly is in Summer pruning of fruit trees.
Strengthen the tree
A well-supplied, vigorous pear tree shrugs off a light rust attack. Aim for a sunny site and a moderate, balanced feeding.
No juniper, no rust. Whoever removes the savin nearby breaks the cycle at the root.
The core rule against pear rust
Frequently asked questions
How do I reliably recognise pear rust?
By bright orange-red spots on the upper leaf side from early summer and the grid-like, brown spore structures on the underside. The fruit is usually not affected. The damage picture is so typical that confusion is hardly possible.
Why must I remove the juniper?
Because the fungus must alternate between pear and juniper. Without the second host it cannot complete its cycle. Removing the savin or susceptible ornamental junipers in the surroundings is therefore the only lastingly effective measure.
What if the juniper is at the neighbour's?
Then only the conversation helps. Many do not know their savin is the cause. As it is toxic and easily replaced, neighbours are often willing to swap it. The spores rarely fly far into the distance.
Can I still eat pears from the affected tree?
Yes. Pear rust sits on the leaves; the fruit generally stays unaffected and edible. Only with very heavy, years-long attack does the harvest suffer, because the tree is weakened overall.
Are there resistant pear varieties?
Some varieties are attacked less strongly than others, but fully resistant ones hardly exist. The lever therefore lies not with the variety but with removing the second host. An often-confused neighbour is fire blight, which works quite differently.
