Ask the head gardener: My fruit trees have leaf curl – what can I do?

Telegraph

09-05-2025

Dear Tom,
We have two apple trees and a pear tree, but over the last few years we have been plagued with leaf curl, which has restricted our crop of fruit. Each winter we have pruned them and we've also given them a thorough winter wash, soaking the trees. They are pruned into a goblet shape and are well mulched, but to no avail. Is there anything we can do now to stop this happening again in the future?
– Suzanne
Dear Suzanne,
It sounds as if you're doing everything humanly possible, Suzanne, to make these fruit trees grow successfully, but the fact that you've been experiencing leaf curl over several years and across both your apple trees and your pear tree is quite the conundrum. It's very difficult to say definitively why your fruit trees have curling leaves over successive years, but there are several reasons that we can explore.
Probably the easiest answer, but equally the most frustrating, is to blame the weather. Stress caused by temperature, drought or even wind can cause leaves to curl on fruit trees. We've obviously experienced a very warm and dry spell, which may have caused some stress to your trees. You are training them into a goblet shape, so they are regularly pruned, and therefore you're creating lots of wounds all over the tree, adding to that stress level through water loss. However, the damage has been reoccurring over a number of years, which makes me think that this reason isn't in fact valid, because we had a particularly wet summer last year, so if the trees experienced the same level of leaf curl, there must be something else going on.
A plant's response to an insect attack will be a curling of the foliage, especially the young leaves. Although there might not be any aphids present on the young shoots, if they have visited the tree previously and caused some damage, that will still cause those leaves to curl. Aphids and leaf-curling midges are two common pests that will attack fruit trees. When it comes to dealing with these pests, an oil-based spray such as SB Plant Invigorator applied on the shoot tips on a weekly basis throughout the growing season can keep their numbers at bay.
As fruit trees become larger, this isn't always the most practical option, and it can be a costly one too. Encouraging lots of predators into your garden – for example, by introducing bird boxes to encourage nesting blue tits, as well as lots of habitats for predatory insects – may help to create more of a diverse ecosystem where predators can help control some of these pest numbers, if indeed that is the issue.
Similarly, fungal attacks such as apple scab and powdery mildew can cause leaf curl on fruit trees. Powdery mildew will present itself as a white powder-like substance on the surface of the leaves, while apple scab tends to produce dark patches on the foliage. Fungicides are available from garden centres, but the practicalities of spraying on a larger tree can be very difficult. Targeting the very shoot tips on a weekly basis may help to control the issue if this response is due to a fungal attack.
A final piece of advice that I can offer is that it may be down to a nutrient deficiency, which may explain the reason why all of the fruit trees are suffering, if they are planted in a similar area in the garden. If this damage is caused by a lack of nutrients, then the fact that you're mulching on an annual basis is certainly helping and probably reducing the severity of the problem. One of the most practical solutions would be to apply a handful of Vitax Q4 (a general fertiliser) once a month, around the base of your tree, concentrating on where the feeder roots are growing, rather than at the base of the trunk.
Apply this fertiliser at a rate of a handful per square metre from March through until June. Switch to sulphate of potash from June through to September. Good plant health and a diverse ecosystem in the garden, including lots of predators, is what we should strive for. Plants aren't so different from us: if we're feeling a little rundown, we're more susceptible to colds and flu. Keep your plants in good health so that their immune system is buoyant, and they too can help fight off any pests or fungal diseases, as both insects and fungal issues tend to be more prevalent on weaker plants.