Why Are My Cassava Leaves Curling?

Red spider mite

Red spider mite (Tetranychus urticae) is the most common pest of cassava grown indoors in the UK. It thrives in warm, dry conditions such as a heated greenhouse, conservatory, or warm living room, and multiplies rapidly in summer. The mites colonise the undersides of the leaves, producing a fine, silky webbing and causing pale, yellowish stippling on the upper leaf surface as they feed by puncturing individual cells. As the infestation progresses, the leaves become pale and washed-out, curl downward, and eventually drop. The webbing can be extensive on heavily infested plants.

What to do

• Introduce the biological control predator Phytoseiulus persimilis as soon as spider mite is detected: the predator reproduces fastest relative to the pest at higher temperatures, making it ideal for warm indoor cassava conditions. Increase humidity by misting the foliage and placing the pot on a gravel tray with water. Remove heavily infested leaves. For severe infestations before biological control can be established, treat with a plant-safe miticide spray.

Cassava mosaic virus

Cassava mosaic disease is caused by a complex of geminiviruses spread primarily by the silverleaf whitefly (Bemisia tabaci). Infected cassava plants show a distinctive yellow-green mosaic pattern on the leaves, with puckering, distortion, and curling of the leaf blade. Affected growing tips are often severely stunted and produce deformed, spoon-shaped leaves. Plants do not recover from cassava mosaic virus. The silverleaf whitefly can persist in heated UK glasshouses year-round and is more common in commercial horticultural settings than in home gardens.

What to do

• Remove and destroy infected plants immediately. Control whitefly populations with yellow sticky traps, biological control (Encarsia formosa parasitoid wasp), or insecticidal soap. Source new cassava plants or cuttings only from healthy, known-clean plants. Do not propagate from infected stem cuttings.

Cold and low light

Cassava requires sustained temperatures above 18°C and high light levels to grow well. In UK homes and conservatories, cool temperatures in autumn and winter cause the leaves to yellow, droop, and eventually curl and drop as the plant shuts down vegetative growth. Insufficient light (below a south-facing window) causes the internodes to elongate and the leaves to become pale and limp. Cassava grown in poorly lit positions develops weak, elongated stems and the leaves curl inward as the plant attempts to maximise light capture.

What to do

• Grow cassava in the warmest, sunniest position available: a heated greenhouse, a conservatory with south-facing aspect, or directly in a south-facing window. Maintain temperatures above 15°C at all times and above 20°C for active growth. In winter, reduce watering significantly and accept some leaf loss; the plant will recover in spring as temperatures and light levels rise. Supplement with a grow light if natural light is insufficient.

Whitefly

Both the glasshouse whitefly (Trialeurodes vaporariorum) and the silverleaf whitefly (Bemisia tabaci) can infest cassava grown under glass in the UK. Whitefly feed by sucking sap from the leaf undersides, producing honeydew and causing the leaves to yellow, pale, and curl at the margins as the cell damage accumulates. Silverleaf whitefly is particularly damaging as it transmits cassava mosaic viruses; glasshouse whitefly does not transmit these viruses but can still cause significant feeding damage.

What to do

• Place yellow sticky traps near cassava plants to monitor and trap adult whiteflies. Use the biological control Encarsia formosa (a parasitoid wasp) for ongoing control in heated glasshouses; introduce early in the season before populations build. For severe infestations, treat with insecticidal soap or a pyrethrum-based spray, applied to the leaf undersides where the insects feed and lay eggs.

Frequently asked questions

Why are my cassava leaves curling?

Cassava (Manihot esculenta) leaves curl most commonly because of red spider mite, cassava mosaic virus (spread by whitefly), or cold and low light in UK indoor conditions. Cassava is a tropical shrub from South America that requires sustained warmth (above 18°C) and high light to thrive; in UK homes and greenhouses, it frequently suffers environmental leaf curl from cool temperatures, draught, and insufficient light during the winter months. Red spider mite (Tetranychus urticae) colonises the undersides of leaves in warm, dry greenhouse or conservatory conditions, producing fine webbing and pale, stippled leaf surfaces; as the infestation advances, the leaves yellow, curl, and drop. Cassava mosaic virus (CMV, spread by the silverleaf whitefly Bemisia tabaci) causes a distinctive yellow-green mosaic on the leaves alongside leaf puckering, curling, and distortion; infected plants do not recover and should be removed to prevent whitefly-mediated spread.

Can I grow cassava in the UK?

Cassava (Manihot esculenta) can be grown in the UK as a conservatory or heated greenhouse plant, or as a temporary outdoor plant in the warmest summer months in the most sheltered, sun-warmed UK gardens. It requires full sun, sustained warmth above 18°C, high humidity, and a long frost-free growing season of at least 8 to 10 months to produce harvestable roots; this is difficult to achieve in the UK without supplementary heating and artificial lighting in winter. Cassava grown as a UK container plant is primarily an ornamental curiosity rather than a practical food crop; the distinctive, deeply lobed leaves are attractive in their own right. Outdoor cassava in the UK is limited to the warmest spots in southern England and should be planted in late May after the risk of frost has passed and brought back under glass before the first autumn frost. Roots may develop on large, well-established outdoor plants in a warm summer, but yields are much lower than in tropical production.

What is cassava mosaic virus?

Cassava mosaic disease (CMD) is a complex of diseases caused by cassava mosaic viruses (CMVs), a group of geminiviruses in the family Geminiviridae. It is the most economically damaging disease of cassava in Africa and parts of Asia, causing yield losses of 20 to 100% in susceptible varieties. The virus is transmitted primarily by the silverleaf whitefly (Bemisia tabaci) and also through infected planting material (stem cuttings). Infected plants show a yellow-green mosaic pattern on the leaves, distortion and puckering of the leaf blade, leaf curling, and stunted growth. There is no cure for infected plants; in UK cultivation, the risk of cassava mosaic virus is low because the silverleaf whitefly is not established outdoors in the UK, but it can be present in heated glasshouses and conservatories where the whitefly persists year-round. If you source cassava stem cuttings for propagation, source them from healthy, known-clean plants.

Is cassava safe to eat raw?

No, raw cassava (Manihot esculenta) is not safe to eat. Both the roots and leaves of cassava contain cyanogenic glucosides (primarily linamarin and lotaustralin) that release hydrogen cyanide (prussic acid) when the plant tissue is damaged and the glucosides come into contact with naturally occurring enzymes. Bitter varieties of cassava have higher levels of these compounds and are particularly dangerous raw. Thorough cooking (boiling, roasting, or frying) destroys the cyanogenic compounds and makes cassava safe to eat; the cooking water should be discarded. Traditional cassava processing methods (grating, pressing, and drying) also reduce cyanide levels effectively. Cassava flour and tapioca (made from cassava starch) are fully safe products that have been properly processed. Sweet varieties of cassava (which have lower cyanide levels) can be made safe by peeling and boiling alone, but bitter varieties require more extensive processing.