Plant problems

Why Are My Acerola Leaves Curling?

Q: Why are my acerola leaves curling?

Acerola (Malpighia emarginata or Malpighia glabra), also called Barbados cherry or West Indian cherry, leaves curl most commonly in the UK because of mealybug infestation, low humidity, scale insects, or cold temperatures. Acerola is a tropical shrub from the Caribbean and tropical Americas and must be grown in a heated UK greenhouse; it requires minimum temperatures of 10 to 12°C at all times and grows best above 18°C. Mealybug (Planococcus citri and related species) is the most common pest of acerola under glass in the UK, appearing as white, cottony clusters in the leaf axils, at the stem joints, and on the young growing tips; affected leaves curl and distort as the insects drain sap from the developing tissue. Low humidity in a heated UK glasshouse in winter causes the small, glossy leaves to dry and curl at the margins. Scale insects (soft scale and brown scale) cluster on the stems and leaf undersides, producing honeydew and sooty mould. Cold temperatures below 10°C cause the leaves to pale, curl, and drop.

Q: What is acerola and why is it grown in the UK?

Acerola (Malpighia emarginata and Malpighia glabra) is a tropical shrub or small tree from the Caribbean, Central America, and northern South America, widely cultivated throughout tropical regions for its small, bright red, cherry-like fruit. Its extraordinary claim to fame is its vitamin C content: acerola is consistently recorded as one of the highest natural sources of vitamin C of any known plant, with fresh fruit containing between 1,000 and 1,700 mg of ascorbic acid per 100g, compared to about 53 mg per 100g in orange juice. This extraordinary concentration has made acerola commercially important as a natural vitamin C ingredient in supplements, fortified foods, and cosmetics; the fruit is powdered, juiced, or processed into extract and sold as a natural, food-derived vitamin C source. In the UK it is grown primarily as a heated greenhouse curiosity and functional health plant; the fruit is produced in clusters of 3 to 4, ripening to bright red and lasting only 3 to 5 days before deteriorating, which is why commercial fresh acerola is almost never seen in UK shops (the fruit must be frozen or processed immediately after harvest). The plant is an attractive greenhouse specimen with glossy leaves and small pink flowers produced in multiple flushes throughout the year in warm conditions.

Q: What does acerola taste like?

Acerola (Malpighia emarginata) has a sweet, tart, cherry-like flavour with a slightly astringent aftertaste and a very high acid content that gives it a characteristic sharpness. The fruit resembles a small, slightly flattened cherry (about 1 to 3 cm diameter); the skin is thin and fragile, the flesh is pale orange-yellow, soft, juicy, and surrounds three small seeds. The flavour is pleasant fresh when fully ripe, with the tartness well balanced by sweetness; underripe fruit is more astringent and sour. The very high vitamin C content does not affect the flavour noticeably. Acerola is widely eaten fresh throughout the Caribbean and tropical Americas and used in juices, smoothies, jams, and ice creams. In Brazil, acerola juice (suco de acerola) is a popular everyday drink sold from street stalls and supermarkets; the frozen pulp is exported to the UK as a smoothie ingredient. The powdered freeze-dried fruit is sold in UK health food shops as a natural vitamin C supplement. UK greenhouse growers who succeed in fruiting acerola report that the fresh berries eaten straight from the plant in summer are a revelation compared to any supplement form.

Q: How do I control mealybug on acerola?

Mealybug is the most troublesome pest of acerola in UK greenhouse conditions and requires persistent, multi-method control. Mealybug colonies appear as white, cottony wax clusters in the leaf axils, at the growing tips, and in any crevice in the stem structure; the insects are mobile and able to spread from plant to plant on contact. To control: dab individual mealybug colonies with a cotton bud soaked in methylated spirits to kill adults on contact; this is effective for small, localised infestations. Apply insecticidal soap or neem oil spray to all plant surfaces, focusing on the leaf axils and growing tips where mealybug hides; repeat every 5 to 7 days for 3 to 4 weeks. Introduce Cryptolaemus montrouzieri (the mealybug destroyer, a predatory ladybird beetle) or Leptomastix dactylopii (a parasitoid wasp) for biological control in the warm greenhouse environment where these predators thrive; these are the most effective long-term controls. Inspect the plant thoroughly at least weekly; mealybug populations rebuild rapidly if control is interrupted, particularly in the warm conditions acerola requires. Isolate newly acquired plants for at least 4 weeks before introducing them to the greenhouse, as mealybug is easily introduced on purchased plants.

Acerola (Malpighia emarginata), also called Barbados cherry or West Indian cherry, is a tropical shrub from the Caribbean with extraordinary vitamin C content: one of the highest of any known plant, at 1,000 to 1,700 mg per 100g of fresh fruit. Grown in UK heated greenhouses as an attractive functional plant with glossy leaves and clusters of small pink flowers, it must be kept above 10°C and protected from the dry air of a heated glasshouse in winter. When the small, glossy leaves curl, mealybug on the growing tips or low humidity are the most likely causes.

Mealybug

Mealybug is the most persistent and damaging pest of acerola in UK greenhouse conditions. The white, cottony colonies appear in the leaf axils, at the growing tips, and in stem crevices; they extract sap and produce copious sticky honeydew that supports sooty mould. When mealybug colonises the young, expanding leaves, the affected tissue curls and distorts as it develops; this distortion persists even after the insects are controlled. Heavy infestations cause leaf yellowing, premature drop, and significant weakening of the plant. Mealybug on acerola can be difficult to eradicate completely because the plant's bushy growth and the insects' ability to hide in crevices allow colonies to persist in sheltered pockets even after apparent control.

What to do

Dab colonies with methylated spirits on a cotton bud to kill adults. Apply insecticidal soap or neem oil spray thoroughly to all plant surfaces every 5 to 7 days for 3 to 4 weeks. Introduce Cryptolaemus montrouzieri or Leptomastix dactylopii for biological control. Inspect at least weekly; populations rebuild rapidly. Isolate new plants for 4 weeks before introducing them to the greenhouse.

Low humidity

Acerola is from the humid Caribbean and coastal tropics and requires moderate to high humidity to maintain healthy foliage. In the dry air of a UK heated greenhouse in winter (when heating significantly reduces relative humidity), the small, glossy leaves develop brown margins and curl inward. Low humidity also greatly increases susceptibility to red spider mite. A digital hygrometer in the greenhouse to monitor humidity levels is a worthwhile investment; acerola does well at 50 to 65% relative humidity.

What to do

Place the pot on a wide gravel tray filled with water. Mist the foliage in the morning. Run a humidifier during the warmest part of the day in winter. Damp down the greenhouse floor and staging regularly. Group acerola with other tropical plants to create a localised humid microclimate.

Scale insects

Soft scale (Coccus hesperidum) and brown scale (Parthenolecanium corni) can affect acerola in UK greenhouse conditions, clustering on the stems and leaf undersides and producing honeydew and sooty mould. Infested leaves yellow and curl. Scale is less immediately dramatic than mealybug on acerola but can build to significant numbers over a winter without active monitoring.

What to do

Scrub scale off stems with a toothbrush and insecticidal soap. Apply insecticidal soap or neem oil spray to all plant surfaces, repeating every 10 days. Introduce Metaphycus helvolus for biological control of soft scale. Inspect stems and leaf undersides at least monthly.

Cold damage

Acerola has no meaningful cold tolerance and is damaged by temperatures below 10°C; below 5°C, significant leaf damage and drop occur, and temperatures near freezing will kill the plant. In a UK heated greenhouse, the main risk is an overnight temperature failure in winter. Cold-damaged acerola leaves turn pale, curl, and drop; the plant will recover and produce new growth if the roots and main stem were not fatally chilled.

What to do

Maintain temperatures above 12°C at all times. Use a minimum thermometer to monitor overnight temperatures. In the event of a heating failure in winter, move acerola to the warmest part of the greenhouse and cover with horticultural fleece. Remove cold-damaged leaves and reduce watering until new growth appears.

Frequently asked questions

Why are my acerola leaves curling?

Acerola (Malpighia emarginata) leaves curl most commonly in the UK because of mealybug infestation, low humidity, scale insects, or cold temperatures. Mealybug appears as white cottony clusters in the leaf axils and growing tips; affected leaves curl and distort. Low humidity in a heated UK glasshouse in winter causes the leaf margins to dry and curl. Scale insects cluster on stems and leaf undersides. Cold temperatures below 10°C cause the leaves to pale, curl, and drop.

What is acerola and why is it grown in the UK?

Acerola (Malpighia emarginata) is a tropical shrub from the Caribbean with one of the highest natural vitamin C contents of any known plant (1,000 to 1,700 mg per 100g of fresh fruit). Grown in UK heated greenhouses as a functional health plant and attractive specimen with glossy leaves and pink flowers. The fruit deteriorates within 3 to 5 days of harvest; it is commercially powdered, juiced, or extracted for use in supplements and fortified foods. Fresh acerola is almost never seen in UK shops.

What does acerola taste like?

Acerola has a sweet, tart, cherry-like flavour with a slight astringency and high acid content. The small, bright red, cherry-like fruit is fragile and soft when ripe, with pale orange-yellow juicy flesh surrounding three small seeds. In Brazil, acerola juice is a popular everyday drink. The powdered freeze-dried fruit is sold in UK health food shops as a natural vitamin C supplement. Fresh berries from a UK greenhouse plant eaten in summer are considered significantly superior to any supplement form.

How do I control mealybug on acerola?

Dab colonies with a cotton bud soaked in methylated spirits to kill adults on contact. Apply insecticidal soap or neem oil spray to all plant surfaces every 5 to 7 days for 3 to 4 weeks, focusing on the leaf axils and growing tips. Introduce Cryptolaemus montrouzieri (mealybug destroyer) or Leptomastix dactylopii (parasitoid wasp) for biological control. Inspect at least weekly; populations rebuild rapidly in warm conditions. Isolate new plants for 4 weeks before introducing them to the greenhouse.