Pineapple diseases and pests: how to spot and control rot and mealybug

In the red soil of Madhupur in Tangail, the 2021 pineapple season closed on a good note. In mid-September the Department of Agricultural Extension (DAE) said pineapple had been grown on 7,186 hectares in the district, with a production target of 266,768 tonnes; growers told The Financial Express that the weather had given them a good yield and a fair price. Yet growers there, as in Srimangal and the Hill Tracts, lose fruit every year to rot, insects and the long road to market.

This guide, first published by The Agro News in October 2021 for farmers and students of agricultural science, explains the main diseases and the main pest of pineapple in Bangladesh: the rot of fruit and leaves, stem and root rot, and the mealybug with the wilt it spreads. It shows how to recognise each problem, what the Bangladesh Agricultural Research Institute (BARI) and university extension services advise, and how to cut losses after harvest; for any chemical, the product and dose come from the upazila agriculture officer.

Pineapple is one of the most important commercial fruits in the world. In Bangladesh it has been called "Swarnakumari" for its beauty, and it is valued for its fragrance and its sweet-sour taste. BARI's Krishi Projukti Hatboi (Handbook on Agro-Technology), ninth edition, published in January 2020, puts the national crop at about 14,400 hectares and total production at about 212,000 tonnes, with an average yield of 14 to 15 tonnes per hectare.

According to the same handbook, pineapple is grown widely in Sylhet, Moulvibazar, Chattogram, the Chittagong Hill Tracts and Tangail, and also in Dhaka, Narsingdi, Cumilla and Dinajpur. In Moulvibazar, Srimangal and the Madhupur area of Tangail it is an important cash crop. The fruit is a good source of vitamins A, B and C, BARI notes.

In Rangamati, the DAE's deputy director told The Business Standard in February 2021 that 55,850 tonnes of pineapple had been produced on 2,130 hectares in ten upazilas of the district the season before, and that early cultivation had spread to 730 hectares.

Madhupur's pineapple has its own history. Cultivation there is traced to 1942, when Mizi Dayamai Sangma, a member of the Garo community, brought 750 pineapple saplings from Meghalaya in India and planted them in Idilpur village.

BARI's handbook describes four varieties in Bangladesh. Honey Queen has yellow flesh when ripe, pointed and raised eyes, spiny leaves and an average weight of about 1 kg; BARI calls it the sweetest pineapple, yielding 25 to 30 tonnes per hectare, grown mostly in Sylhet, Chattogram and the Hill Tracts, and fit for export.

Giant Kew, known locally as kalendar, ranks first in both area and production. The ripe fruit is greenish with pale yellow flesh, broad flat eyes and an average weight of about 2 kg; the leaves are nearly spineless and the taste is sweet and sour. BARI gives a yield of 30 to 40 tonnes per hectare and says it is grown most in Sylhet, Moulvibazar and Tangail. Ghorashal, reddish with creamy white flesh, is limited to Dhaka and Narsingdi, and Jaldhupi is described as suitable for processing.

The type of planting material also affects the crop. In a BARI trial at the Fruit Research Station in Jaintiapur, Sylhet, run from November 1986 to August 1988 and published in the Bangladesh Journal of Agricultural Research in 1992, plants grown from slips yielded only 6.60 tonnes per hectare, against 22.29 tonnes from crowns and 20.39 tonnes from shoot suckers. A disease or pest carried on suckers, slips or crowns moves straight into the new field, which is why most of the measures below begin with healthy planting material.

The first problem affects both fruit and plant. Water-soaked spots appear on the fruit, then turn yellow and later dark brown and blackish. The tissue of the affected part softens and rots, and an infected ripe fruit gives off a characteristic smell. If the leaves are infected, the whole plant can turn black and rot.

India's National Horticulture Board describes the same pattern under leaf and fruit rot caused by the fungus known today as Ceratocystis paradoxa, also called Thielaviopsis paradoxa. It notes that the fungus rots the base or butt of planting material that is not dried and is packed with little air, that it can enter older plants through wounds made at the collar during weeding, and that in severe cases the whole plant may turn dark and rot within two or three days.

The same fungus causes the black rot or soft rot of harvested fruit. According to the Pineapple Research Station of Kerala Agricultural University (2012), it enters mainly through the broken fruit stalk, bruises and cracks, is most active in warm, wet weather and develops three to four days after harvest. It is the major post-harvest disease of fresh pineapple, worst when fruit travels far without refrigeration.

The control measures are these:

• Keep the orchard clean, and remove rotten fruit, pineapple refuse and rejected fruit from in and around the field and the packing place.
• Use suckers from healthy plants as planting material, and never collect suckers from an infested area (National Horticulture Board).
• Before planting, dry the suckers in mild sunlight. Kerala Agricultural University advises storing planting material in a single layer with the cut butts exposed to the sun, and says that curing the base in this way greatly reduces losses. Do not leave a portion of fruit attached to a crown that will be planted.
• Handle fruit carefully at harvest so that it is not bruised or scuffed, and set aside sunburnt or damaged fruit, whose small skin cracks are readily infected.
• Clean and disinfect the baskets, crates and the packing shed before the harvest is packed. Kerala Agricultural University advises treating the shed with a recommended disinfectant once a week.
• Treat the cut stalk end of harvested fruit promptly: the university advises dipping the base of the fruit in a recommended fungicide within five hours of harvest, especially in warm, wet weather. Ask the upazila agriculture officer which product is approved and at what strength.

Stem rot, the second disease, is caused by Phytophthora parasitica. In the field, the leaves first turn yellow and then brown, the base of the stem and the roots turn black and begin to rot, and in the end the whole plant dies.

The University of Hawai'i's College of Tropical Agriculture and Human Resources (CTAHR) explains the cause in its 2015 publication "Heart and Root Rots of Pineapple". Phytophthora and Pythium are water moulds, fungus-like organisms that live in the soil, and Phytophthora parasitica is among the most common species on pineapple. They thrive in wet soil: swimming spores move through soil water to the roots, spores in soil on tools, footwear and tyres or splashed by rain reach the crown, and resting spores survive in the soil for years.

CTAHR describes two forms. In heart rot, the white tissue at the base of the youngest leaves goes soft and rotten, the infected leaves pull out easily, and in susceptible varieties the rot can move up the stalk and rot the fruit. In root rot the plant grows slowly, the leaves turn yellow, brown or reddish purple and later curl and die, and a plant with dead roots comes away easily when the crown is tugged. Kerala Agricultural University adds that three- to four-month-old crown plantings are the most susceptible.

Both diseases are worst in high rainfall and in poorly drained soil, so drainage is the first defence. The control measures are these:

• Keep the orchard clean and tidy, and remove plants that have rotted rather than leaving them in the field.
• Make sure water does not collect in the orchard. BARI's handbook advises levelling the land so that rainwater stands nowhere, making beds 15 cm above the ground and 1 metre wide with drains of 40 to 50 cm between them, and cutting drains during the rainy season so that water does not stand at the base of the plants.
• Avoid planting too deep and keep soil out of the heart of the plant at planting, as Kerala Agricultural University advises.
• Clean tools and containers carrying soil from another field, and do not move soil from an infested patch to a clean one (CTAHR).
• Choose healthy planting material from a disease-free field. CTAHR notes that no pineapple variety yet has good resistance to these water moulds; the hybrid MD-2 shows the most resistance when conditions favour the plant, but not when they favour the disease.
• Dipping planting material in a fungicide before planting is the usual chemical step, especially where disease has been a problem, CTAHR says. The choice of product and dose should come from the upazila agriculture officer, because authorities differ: India's National Horticulture Board, for example, warns that copper fungicides can scorch pineapple leaves.

The main insect pest named in the guide is the mealybug, known in Bengali as chhatra poka. It sucks sap from the leaves, stem and fruit and leaves wounds. If it attacks the roots or the joint of stem and root, the plant wilts; infested fruit rots; and a virus that enters at the feeding site causes pineapple wilt.

The species chiefly involved is the pink pineapple mealybug, Dysmicoccus brevipes. CTAHR's Crop Knowledge Master describes the adult female as plump, convex and pinkish, living at the base of the plant on the lower stem, the butts and exposed roots. It causes two forms of wilt: a quick wilt after a short period of feeding by a large colony, which turns the leaves yellow or red, and a slow wilt after larger colonies develop, in which the leaf tips brown and the outer leaves droop. The wilt usually spreads from the field edge inwards.

Kerala Agricultural University (2012) describes mealybug wilt as a virus disease spread by mealybugs. The first sign is a slight reddening of the leaves about halfway up the plant; the leaves then turn pink, lose their stiffness, roll down at the margins, and the leaf tips die. Young plants show symptoms two to three months after the insects feed, older plants up to 12 months later. The disease is probably introduced on planting material that does not yet show it.

Ants collect the honeydew mealybugs produce, protect them from predators and move them between plants. CTAHR names the big-headed ant, Pheidole megacephala, as the main ant tending the mealybug in Hawai'i, and notes that natural enemies such as the mealybug ladybird Cryptolaemus montrouzieri give little control while ants guard the colonies. Without ants, it says, mealybug populations stay small.

The control measures are these:

• Take suckers only from wilt-free fields. Kerala Agricultural University advises that a field where more than 10 percent of plants show wilt should not be used as a source of planting material.
• Pull out and destroy wilted plants by hand while fewer than 3 percent of plants are affected, the university advises; above that level it recommends insecticide treatment against both the mealybugs and the ants.
• Keep field edges free of weeds and rubbish, which shelter ants and mealybugs, and control the ants that tend them.
• After harvest, clear the field: the original guide advises burning the dry leaves and debris, and CTAHR likewise advises turning over previously infested fields and removing and burning all crop residue.
• If an insecticide is needed, ask the upazila agriculture officer which product is approved for pineapple in Bangladesh and at what dose, and follow the label and its waiting period before harvest.

The guide also notes that much of the damage happens after the fruit ripens: in storage, processing, transport and marketing. BARI's handbook explains why. Most of the country's pineapple is harvested between June and August, the same months as mango, jackfruit, litchi, guava and jamun, so prices fall, and much fruit rots when it cannot be moved on rainy days.

BARI says 60 to 65 percent of the season's pineapple is sold within the country and only 5 to 7 percent is processed into jam, jelly, squash and juice, while for lack of proper transport and storage about 20 to 40 percent is wasted. With better transport, packaging and temperature control, its Postharvest Technology Division found, pineapple can be kept fresh for three to four weeks.

• Pack mature, fresh fruit of even size in rows in wooden or large plastic crates so that it is not bruised. BARI says a crate of 60 by 36 by 32 cm holds 20 to 25 pineapples, and a five-ply carton 12 to 15.
• For long distances, use refrigerated trucks or reefer vans that hold the fruit at 18 to 20 degrees Celsius.
• For longer storage, BARI found that two Giant Kew fruits kept in a 1 percent perforated polypropylene bag of 34 microns in a cool room at 11 degrees Celsius and about 88 percent humidity stayed fresh for up to four weeks.

Spreading the harvest also reduces losses. BARI's handbook describes hormone treatment to bring plants into flower at a chosen time, and in Rangamati growers using Ethrel told The Business Standard in February 2021 that they harvested early and that wholesalers paid Tk 8 to 9 a fruit, against Tk 4 to 5 in the peak season. The Financial Express reported in September 2021 that some Madhupur growers were alleged to use excessive chemicals for ripening and colour, and DAE officials said they were urging growers not to.

Since many of these problems start with the planting material and the soil, prevention starts at planting. BARI gives mid-Ashwin to mid-Agrahayan (October to November) as the right time to plant pineapple, and mid-Magh to mid-Falgun (February) where irrigation is available. Loam and sandy loam soils suit it best.

BARI advises planting two rows on each 1-metre bed, with 50 cm between rows and 30 to 40 cm between plants. The field should be kept weed-free. Flowers usually appear from mid-Magh to mid-Chaitra (February to March), 15 to 16 months after planting, and the fruit ripens from mid-Jaistha to mid-Bhadra (June to August).

A farmer who sees rot, wilt or mealybug colonies should take a sample or a clear photograph to the upazila agriculture office of the DAE or to the nearest BARI research station. Plants with heart rot can be saved only if treated soon after symptoms appear, Kerala Agricultural University notes.

The officer can confirm the problem, say whether a chemical is needed at all, and name the product registered for pineapple in Bangladesh with its dose and the waiting period before harvest.

Photo: Snsadat55 / Wikimedia Commons (CC BY-SA 4.0)

Sources: The Agro News, Bangladesh Agricultural Research Institute (Krishi Projukti Hatboi, 9th edition, 2020), Bangladesh Journal of Agricultural Research, University of Hawai'i CTAHR, Kerala Agricultural University, National Horticulture Board of India, The Financial Express, The Business Standard, Banglapedia, Wikipedia