Leaf-curl diseases caused by species of Taphrina fungi often have little long-term impact on plant health but the damage is unsightly and can lead to customer rejection.
Peach leaf curl, caused by Taphrina deformans, is the best known and most widely studied, being of widespread economic significance in peach fruit-producing regions of the world. For growers of ornamental trees, it is a disease limited to peaches, nectarines and sometimes almonds and apricots, but it can be destructive and disfiguring when it does occur.
Taphrina deformans infection disturbs the morphology of the host, leading to distorted leaves and stems. Leaf puckering and blistering can be confused with damage caused by mites and aphids. Some species of the fungus are responsible for witches’ brooms on trees.
Other species of Taphrina affect a range of ornamental and fruiting species in the UK and Ireland. Taphrina caerulescens is a leaf-curl disease of native oaks and although widespread outbreaks on red oak species have been reported, the disease is considered to be rare.
Chemical control is based on copper fungicides applied in early spring and before bud break to target the overwintered spores, but some peach varieties are sensitive to copper. Once the symptoms become apparent at bud burst, it is often too late to spray. Trees grown or kept under protection are rarely affected.
How to recognise it
Initial symptoms occur in early spring, when leaves pucker, curl, blister and thicken. Shoots may also become deformed. As the disease advances, the leaves become lighter in colour or yellow and then red or purple. A few weeks later, a white or greyish velvety bloom develops on the upper surfaces of the deformed leaves as the spore sacs emerge. Infected foliage turns brown and starts to fall, which can leave the tree almost bare.
This leaf loss weakens the tree, especially if it is subject to recurring attacks. Trees will produce a second flush of foliage in early summer, which can escape infection if weather is dry.
The disease will sometimes infect flowers and fruit. Flowers shrivel prematurely and drop, while fruit becomes covered in blistered patches. Taphrina pruni causes the disease known as "pocket plums" — distorted and shrivelled fruit bearing no stones.
In cherries, Taphrina minor induces symptoms that are similar to peach leaf curl.
On oaks, Taphrina caerulescens causes pink/purple leaf blisters, which turn brown. It is rare but can be found on native species in the North and the South West, where weather can be mild and damp.
Taphrina aurea produces bright-yellow blisters on the leaves of poplar, while Taphrina ulmi causes green blisters that turn brown on elm. Taphrina bullata infects pears, resulting in brown leaf blisters that look similar to those produced by pear leaf blister mite.
On alders, Taphrina tosquinetii leads to severe shoot and leaf distortion, while Taphrina sadebeckii causes yellow leaf blisters.
New infections are initiated by spores that overwinter lodged in tree bark and on bud scales. The spores that are blown or carried by rain into the buds germinate in cool, wet weather in early spring to infect emerging leaves.
The fungal mycelium spreads between the leaf epidermis and cuticle, secreting growth-regulating chemicals, which cause the plants’ cells to divide abnormally.
The mycelium produces large numbers of spore-containing sacs, which push up through the leaf surface. The spores are discharged in late spring and summer, and are spread by air currents and water splash. Disease development stops in warm, dry weather.
Treatment: biological control
Some growers have had moderate success using a bacterially-loaded compost tea formulation. Repeated applications throughout the year can help to maintain a good covering of beneficial micro-organisms on leaf and stem surfaces providing a competitive environment with pathogens.
Treatment: cultural control
• Commercially, there is no cost-effective cultural control.
• For valuable specimen trees, picking off and burning visibly infected leaves before the bloom of spores develops will reduce infection the following year.
• Breeding of varieties resistant to the disease is continually being investigated.
Treatment: chemical control
Active ingredient Bacillus subtilis strain QST 713
Formulation Serenade ASO* (Bayer)
Action(s) Protectant action. Product can be mixed with copper-based fungicides. Research has shown that Bacillus subtilis has an effect on bacterial infections and may also have an effect on Taphrina spp.
Active ingredient Copper oxychloride
FRAC code M1
Formulation Cuprokylt* (Certis)
Action(s) Protectant action on outdoor ornamentals* with on-label use for a range of edible crops. Avoid rain before and after application for maximum effect. Avoid run-off.
Fully updated by Dove Associates
Use plant protection products safely. Always read the label and product information before use.
* Extension of Authorisation (EAMU) required for use in protected and outdoor ornamental plant production. Download your hard copy from https://secure.pesticides.gov.uk/offlabels/search.asp. An EAMU is applied at grower risk.
Dove Associates shall in no event be liable for the loss or damage to any crops or biological control agents caused by the use of products mentioned.