The Top Garden Diseases and How to Prevent them

The Plant Health team at RHS Science has published its annual disease ranking, revealing the top ten problems for gardeners in 2023.

While fruit trees continue to be under threat following the rise in fruit tree diseases in 2022, four new diseases not seen in the rankings before have also entered the field.

A damp spring and summer have contributed to the prevalence of some of these new diseases, with blossom wilt of fruit trees, pocket plum, tulip fire and slime flux all joining the top ten list for the first time.

Increased planting of fruit trees in recent years is thought to be another contributing factor, with many gardeners turning to heritage varieties that could be more prone it disease. Apples, pears and prunus were among the top five hosts of the diseases.

Wet weather in the spring of 2023 provided the perfect conditions for tulip fire, a fungal disease causing brown spots and twisted, withered leaves. The damp spring is also thought to be responsible for the prevalence of pocket plum, which produces inedible, elongated, hollow fruits with no stone.

The Top Ten Garden Diseases
Pocket Plum on a Prunus Domestica.

Slime flux took the tenth spot in the chart, a disease which troubles a wide variety of trees and shrubs, as well as clematis. It is thought that the bacteria responsible for slime flux colonise trees via their roots, so its prevalence may be due to the wet winter last year which resulted in waterlogged soils.

There was also a rise in reported cases of rose black spot and pear rust, both of which can be attributed to the warm and wet summer weather.

Honey fungus remained in the top spot of the 28th year running. It’s prominence is partially due to the Armillaria fungus having a large host range of over 140 garden plants, particularly large woody ones. Honey fungus causes dramatic symptoms, including cracked and bleeding bark, failure to flower and plant death.

How to Minimise Plant Disease in your Garden

Planting the right plant in the right place is a key factor in minimising disease. Other preventative measures include practising good plant care and hygiene, including mulching plants with an organic mulch, such as homemade compost or well-rotted manure while the soil is moist.

It is also important to prune and remove any dead or diseased material at the right time of year. Apple and pear trees should be pruned in the winter while they are still dormant, while prunus should be pruned in summer when silver leaf is less prevalent.

To reduce the spread of plant diseases:

The Top Ten Garden Diseases
Slime flux on a birch.
  • Wear footwear and outerwear that can easily be kept clean.
  • Clean footwear and outerwear to ensure they are visually free from soil and organic debris.
  • If you are revisiting an infected tree, plan to visit highest-risk sites last.
  • Clean your hands with sanitising gel (or soap and water) and tools (e.g. tape measure) with bacterial wipes or via a spray bottle with a bleach solution (1: 9 bleach/water) between touching trees, to prevent spreading pests and diseases between trees.
  • If taking samples, for example a leaf to examine for signs of a gall on the leaf closely later, clean and disinfect cutting tools and hands after each sample with antibacterial wipes or gel.
  • Keep any samples in sealed containers.

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