Why Are My Blackberry Leaves Curling?
Blackberry (Rubus fruticosus) is a vigorous fruiting plant that grows with little intervention in UK gardens and hedgerows, producing heavy crops of berries from midsummer through to autumn. Garden-grown blackberry varieties have been selected for thornlessness, large fruit, and improved disease resistance compared to wild bramble, but they remain susceptible to cane and leaf mite and rust. Both cause distinctive leaf symptoms: the mite produces silvery-yellow discolouration and upward leaf margin rolling, while rust produces the unmistakeable orange-yellow powdery pustules that many gardeners first encounter with surprise on the underside of otherwise healthy-looking leaves.
Cane and leaf mite
Blackberry cane and leaf mite (Phyllocoptes gracilis) is a microscopic eriophyid mite, invisible to the naked eye, that feeds on the cells of blackberry leaves. The damage it causes is distinctive: the leaf margins roll upward, and the upper surface of the leaf develops a pale, silvery, metallic, or yellowish discolouration that spreads inward from the leaf edges as the mite population grows through the season. In heavy infestations the silvery-yellow area covers most of the upper leaf surface. The mites overwinter inside buds and in the crevices of cane bark, which makes complete eradication very difficult once they have established on a plant.
What to do
- Light infestations cause cosmetic damage only and can be tolerated on an otherwise healthy plant. The blackberry crop is rarely significantly affected by moderate cane and leaf mite infestation.
- Remove and destroy heavily infested canes at the end of the fruiting season in autumn, along with any canes that are not needed for the following year's fruiting. This reduces the overwintering mite population significantly.
- A sulphur-based spray applied at bud burst in spring, before the mites emerge from their overwintering sites in the buds, reduces the season's mite population. Repeat 2 to 3 times at 10-day intervals. Sulphur is approved for organic use and is the most practical chemical control available to home gardeners.
Blackberry rust
Blackberry rust (Phragmidium violaceum) is a fungal disease that produces vivid orange-yellow or brown pustules on the underside of blackberry leaves, with corresponding yellow patches on the upper surface. The pustules are the rust's spore masses and are very distinctive once recognised. Affected leaves may curl slightly and drop prematurely. Blackberry rust is most common in wet summers and in poorly ventilated positions, and is worse on susceptible varieties.
What to do
- Remove and destroy affected leaves as soon as rust symptoms appear. Collect and destroy all fallen leaves in autumn: the rust overwinters in leaf debris and re-infects new growth in spring.
- Improve air circulation: train and tie canes properly and remove excess canes in summer so that air can move freely through the canopy.
- Copper-based fungicide sprayed at bud burst and repeated fortnightly through spring suppresses rust infection. Several applications are needed for useful control in a susceptible variety in a wet season.
- For persistent rust problems, replace with rust-resistant varieties such as 'Chester', 'Loch Tay', or 'Oregon Thornless'.
Aphids
Blackberry aphid (Amphorophora rubi) and related species colonise blackberry growing tips in spring and early summer, causing the young leaves to curl inward around the feeding colonies. Aphid infestations on blackberry are usually self-limiting: natural predators establish quickly once the aphid population builds, and the vigorous blackberry plant outgrows light infestations rapidly.
What to do
- Inspect growing tips from May. Remove small colonies by hand or with a jet of water. Insecticidal soap is effective if colonies are large. Avoid broad-spectrum insecticides that kill beneficial predators as well as aphids.
Drought
Wild blackberry is notably drought-tolerant due to its deep roots, but garden varieties growing in confined beds or trained against walls are more susceptible to drought stress. Drought causes the leaf margins to curl upward and the leaves to develop a dull, greyish-green colour. Water stress during fruit development reduces berry size and causes berries to ripen unevenly.
What to do
- Apply a thick mulch along the base of trained blackberry canes. Water during fruit development in dry summers. Blackberries on heavy soils are significantly more drought-tolerant than those on light, free-draining soils.
Frequently asked questions
Why are my blackberry leaves curling?
Blackberry leaves curl most often because of blackberry and raspberry cane and leaf mite (Phyllocoptes gracilis), blackberry rust (Phragmidium violaceum), or aphids. The cane and leaf mite is a microscopic eriophyid mite that feeds on the underside of blackberry leaves, causing the leaf margins to roll upward, and the affected areas to develop a silvery, yellowish, or rusty discolouration. Blackberry rust produces distinctive orange-yellow or brown powdery pustules on the underside of the leaves, associated with yellow patches on the upper surface; affected leaves may curl slightly. Aphids on the growing tips cause the young leaves to curl inward around the feeding colonies in spring and early summer.
What is cane and leaf mite on blackberry?
Blackberry cane and leaf mite (Phyllocoptes gracilis, also known as the raspberry leaf and bud mite) is a microscopic eriophyid mite that is too small to see with the naked eye but causes distinctive visible damage to blackberry and raspberry leaves. The mites feed by piercing the leaf cells on the underside of the leaves, causing the leaf margins to roll upward and the upper leaf surface to develop a characteristic silvery, metallic, or yellowish discolouration that spreads from the leaf margins inward as the season progresses. In heavy infestations, the silvery-yellow discolouration covers much of the upper leaf surface. The mites overwinter in the folds of buds and under scales on the canes, making them very difficult to eradicate once established. Light to moderate infestations cause cosmetic damage that does not significantly reduce the blackberry crop.
How do I identify blackberry rust?
Blackberry rust (Phragmidium violaceum) produces very distinctive symptoms that are easy to identify once you know what to look for. On the upper surface of the leaves, yellow or orange patches appear from late spring onward. On the underside of these patches, small, raised, orange-yellow or reddish-brown powdery pustules (the rust spore masses) are clearly visible, often in clusters or rings. Later in the season, the pustules may turn darker brown or black as they produce the overwintering spore stage. Affected leaves may curl slightly and yellow around the infected areas. Blackberry rust is most common in wet summers and is worse on plants in humid, poorly ventilated positions. The disease does not typically kill established plants but severely infected leaves drop prematurely, weakening the canes.
How do I get rid of blackberry rust?
Blackberry rust (Phragmidium violaceum) cannot be eradicated from an infected plant, but its severity can be reduced through cultural and chemical controls. Remove and destroy any leaves with rust symptoms as soon as they appear: do not compost them. Collect and destroy all fallen leaves in autumn, as the rust overwinters in fallen leaf debris and re-infects the plant the following spring. Improve air circulation around the canes by training and tying them properly and removing overcrowded or crossing canes. Avoid overhead watering; water at the base of the plant instead. Copper-based fungicides applied from bud burst in spring and repeated every 10 to 14 days through spring and early summer provide some suppression of rust infection. For persistent problems, replacing with rust-resistant blackberry varieties is the most effective long-term solution.