Plant problems

Why Are My Loganberry Leaves Curling?

Q: Why are my loganberry leaves curling?

Loganberry (Rubus loganobaccus, a hybrid of blackberry and raspberry) leaves curl most commonly in the UK because of aphid infestation, cane spot (Elsinoe veneta), raspberry leaf and bud mite (Phyllocoptes gracilis), or spur blight (Didymella applanata). The raspberry aphid (Amphorophora idaei) colonises the growing tips of loganberry canes in spring, causing the young leaves to curl, crinkle, and cup downward. Cane spot (Elsinoe veneta) is a fungal disease of loganberry and related hybrids; it causes small, purple-edged spots on the canes and leaves, and when it infects the cane near a node, it can cause the shoot tip above to curl and wilt. Raspberry leaf and bud mite causes an irregular, crinkled, puckered distortion of the youngest leaves, most visible on the shoot tips in spring. Spur blight causes dark lesions at the nodes that girdle the cane and cause the shoot tip above to droop and curl.

Q: What is the history of the loganberry?

Loganberry (Rubus loganobaccus) was first noted in the garden of James Harvey Logan, a lawyer and amateur horticulturist, in Santa Cruz, California, around 1880. Logan was attempting to cross local wild blackberries to produce a superior fruit; the loganberry appeared as an unexpected seedling, possibly a spontaneous natural hybrid between a blackberry (Rubus ursinus) and a red raspberry (Rubus idaeus). Logan propagated and distributed the plant, which was introduced to the UK in the 1890s and became popular in UK kitchen gardens and allotments through the early twentieth century, valued for jam-making and bottling. The flavour of loganberry is distinctly sour-sweet and intensely flavoured, more tart than either of its parents and too acidic for many people to enjoy fresh; it makes outstanding jam, juice, and wine. Loganberry has now been largely replaced in UK gardens by tayberry (1979) and other modern hybrids that are sweeter, larger-fruited, and more productive, but it retains a devoted following among those who value its intense, complex flavour. Thornless loganberry varieties exist and are easier to manage in a small garden.

Q: What does loganberry taste like?

Loganberry (Rubus loganobaccus) has an intensely flavoured, tart, sour-sweet taste that is considerably more acidic than either blackberry or raspberry. The large, dark red, cylindrical berries have a strong, complex flavour with notes of both parents, but with a pronounced sharpness that makes them too sour for many people to eat fresh in quantity; they are best appreciated in cooking, where the acidity drives an outstanding jam, jelly, juice, or wine. Loganberry jam has a deep crimson colour and a rich, complex flavour considered by many to be superior to raspberry or blackberry jam. The berries ripen in July and August and drop from the plant readily when fully ripe; they do not store well and should be processed quickly after picking. Fresh loganberries are eaten with sugar and cream in the same way as raspberries; the tartness pairs well with sweetened cream. Loganberry wine and loganberry gin are considered speciality products by small UK producers.

Loganberry (Rubus loganobaccus) is a hybrid of blackberry and raspberry first noted in the California garden of James Harvey Logan around 1880 and introduced to UK gardens in the 1890s. It produces large, dark red, cylindrical berries with an intensely tart, sour-sweet flavour outstanding for jam, juice, and wine. Though largely replaced by tayberry in modern UK gardens, it retains a devoted following for its complex flavour. As a close relative of raspberry, it shares the same pest and disease spectrum, with the added susceptibility to cane spot that makes it more demanding than tayberry to manage.

Aphids

The raspberry aphid (Amphorophora idaei) is the most common cause of leaf curl on loganberry canes in spring. Colonies establish on the undersides of the young leaves at the growing tips from April onward, causing them to curl and cup downward; heavily infested tips become distorted and stunted. The raspberry aphid is also a vector of raspberry mosaic virus complex, a group of viruses that cause pale mottling, leaf distortion, and reduced cropping; early aphid control is therefore important not just for the immediate plant health but for preventing long-term viral infection of the planting.

What to do

Check growing tips weekly from April. Pinch off and destroy the most infested tips. Apply insecticidal soap or neem oil spray to the shoot tips and leaf undersides every 7 days. Encourage natural predators. Avoid high-nitrogen feeding in spring, which produces the soft growth aphids prefer. Replace any plants showing persistent mottling or distortion that does not resolve with aphid control; these may have acquired a viral infection.

Cane spot

Cane spot (Elsinoe veneta) is the fungal disease most specifically associated with loganberry in UK gardens; loganberry is significantly more susceptible than tayberry or blackberry. The disease appears in spring and early summer as small, circular, purplish-red spots on the young canes and leaves; the spots develop silvery-white centres and, in severe cases, split and crack the cane. When lesions girdle a node, the shoot tip above wilts and curls over, resembling drought stress. Cane spot spreads by splash-dispersed spores in wet weather and is most severe after a wet spring and summer.

What to do

Remove and destroy all infected canes at ground level after harvest. Improve air circulation by thinning to 8 to 10 canes per plant. Avoid overhead watering that wets the canes. Apply a copper-based fungicide spray in early spring as new canes emerge, and repeat every 14 days during wet weather. If cane spot is recurrent and severe, consider replacing with a tayberry, which has significantly better resistance.

Raspberry leaf and bud mite

Raspberry leaf and bud mite (Phyllocoptes gracilis) affects loganberry as well as raspberry and tayberry. The invisible microscopic mites overwinter under bud scales and move to developing leaves in spring, causing an irregular, puckered, crinkled distortion of the leaf surface, most visible on the youngest leaves at the shoot tips; affected leaves have a characteristic fan-like crumpling with pale yellowish mottling. The symptom is distinct from aphid curl (which cups the leaves downward) and from cane spot (which causes spots and tip wilt). No chemical control is available to home gardeners; heavily affected plants should be removed.

What to do

Remove and destroy heavily affected shoot tips. If most of the plant shows symptoms, remove and replace with certified mite-free stock. Do not propagate from affected plants. Buying certified, mite-tested stock is the most effective prevention.

Spur blight

Spur blight (Didymella applanata) causes dark brown or purple lesions to develop around the nodes on the current season's loganberry canes, particularly in the lower half of the cane. As the lesion expands it girdles the node, killing the lateral shoots (spurs) and causing them to wilt and curl. Severely affected canes produce poor crops the following year; in a bad year spur blight can reduce yields dramatically. Spur blight spreads by splash-dispersed spores in wet conditions and overwinters on infected canes.

What to do

Cut out and destroy all infected canes at ground level after fruiting. Do not compost infected material. Apply a copper-based fungicide in early spring. Improve air circulation by thinning canes. Avoid overhead watering. Grow loganberry on a well-spaced trellis or wire system to keep the canes off the soil and allow rapid drying after rain.

Frequently asked questions

Why are my loganberry leaves curling?

Loganberry (Rubus loganobaccus) leaves curl most commonly in the UK because of aphid infestation, cane spot (Elsinoe veneta), raspberry leaf and bud mite (Phyllocoptes gracilis), or spur blight (Didymella applanata). The raspberry aphid colonises growing tips in spring, causing leaves to curl and cup downward. Cane spot causes purplish spots on the canes and leaves and can cause tip wilt and curl at affected nodes. Leaf and bud mite causes an irregular, puckered, fan-like distortion of the youngest leaves. Spur blight causes dark lesions at nodes that kill the shoots above.

What is the history of the loganberry?

Loganberry (Rubus loganobaccus) was first noted in the California garden of James Harvey Logan around 1880, appearing as a probable spontaneous hybrid between blackberry and raspberry. It was introduced to the UK in the 1890s and became popular in kitchen gardens through the early twentieth century, valued for its intense flavour in jam, juice, and wine. It has now been largely replaced in UK gardens by tayberry and other modern hybrids, but retains a following for its complex, tart flavour.

What is cane spot on loganberry?

Cane spot (Elsinoe veneta) is a fungal disease that particularly affects loganberry; it causes small purplish spots with silvery centres on the canes and leaves, and can cause tip wilt and curl when lesions girdle a node. Loganberry is significantly more susceptible than tayberry or blackberry. Control by removing infected canes, improving air circulation, and applying copper-based fungicide in early spring. Recurrent severe infection is a reason to consider replacing loganberry with tayberry.

What does loganberry taste like?

Loganberry has an intensely tart, sour-sweet flavour considerably more acidic than either blackberry or raspberry, making it too sharp for many people to eat fresh in quantity. It is outstanding for jam, jelly, juice, and wine; loganberry jam has a deep crimson colour and a rich, complex flavour. The large, dark red, cylindrical berries ripen in July and August and drop readily when ripe. Loganberry wine and loganberry gin are considered speciality products by small UK producers.