Fruit trees under threat

n The Royal Horticultural Society (RHS) has released its annual disease ranking, revealing the most prevalent problems for gardeners in 2022.

The top ten list shows an increase in diseases of fruit trees, nine of the top eleven have the potential to impact fruit crop, cause leaf defoliation and even plant death. These diseases are largely linked to the extreme weather conditions we are seeing under climate change, including periods of drought, high temperatures and heavy rainfall which cause plants to become stressed and therefore more susceptible to problems. An uptick in planting of fruit trees in gardens in recent years, including heritage varieties that could be more prone to disease, is also thought to be a factor. There were a high number of enquiries about brown rot of fruit, apple and pear scab and silver leaf, which most often kills Prunus fruit trees. These pathogens can ruin fruit and cause blossom to wilt in spring. Damage to fruit can be a particular concern for gardeners, as it affects their crop and many diseases cause very visible problems.

The list continues to be topped by honey fungus, which has taken the number one spot every year since the list was first published in 1995. The fungus has a large host range of more than 140 garden plants, particularly large woody ones, and results in dramatic symptoms, including death, cracked and bleeding bark and failure to flower. Stress is known to leave plants more susceptible to honey fungus.

To minimise plant disease this year, gardeners are advised to ensure the right plant is in the right place, and should consider good plant care and hygiene, including mulching plants now while the soil is moist, ready to trap water in case of another dry summer, and pruning any dead or diseased material at the right time of year. For apple and pear trees this can be done in winter while they are still dormant, while Prunus should be pruned in summer when silver leaf is less prevalent.

Liz Beal, RHS Plant Pathologist, said, “The prolonged drought last summer followed by a wet and mild autumn provided the perfect conditions for fungi to spread, so it is unsurprising that we have seen an increase in many diseases, particularly in fruit trees which can be very susceptible to rot and other fungi. Gardeners can help combat many of the most common diseases in our ranking by practising good hygiene, keeping tools clean and removing diseased plant material from their gardens. Providing the preferred conditions for the plants in your garden can also help ensure plants do not become stressed and less able to fight off infection.

“The RHS is also calling on gardeners to remain vigilant to new plant problems. For example, blueberry rust could become more of a concern as an increasing number of gardeners try out crops that were previously the preserve of warmer climates.”

The RHS Plant Health team uses the disease ranking to inform their research and advice. Ongoing research projects at RHS Garden Wisley’s Hilltop: Home of Gardening Science include investigating the efficacy of silicon as a treatment for rose black spot, the prevalence of honey fungus spread by spores versus underground mycelium to help inform management and whether Phytophthora root rot is still present in previously cleared areas. RHS members get free access to the charity’s one-to-one Gardening Advice Service, available by phone or email. Find out more about becoming a member at: www.rhs.org.uk/join

RHS advice pages are available for everyone, for further information, visit: www.rhs.org.uk/advice

The top diseases for 2022 are:

1. Honey fungus

2. Phytophthora root rot

3. Powdery mildew on Prunus (cherry laurel)

4. Rose black spot

5. Peach leaf curl

6. Brown rot of fruit

7. Silver leaf

9. Apple and pear scab

= Pear rust

= Apple and pear canker

= Bacterial leaf spot and canker of Prunus (fruit trees)