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Pineapple wilt disease (380)

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Photo 1. Pink, inwardly curling leaves of pineapple with pineapple mealybug wilt disease.

Photo 2. Plants showing pink, rolled, leaves typical of pineapple mealybug wilt disease. The 'wilt' symptoms are due to root decay, caused by virus infection.

Photo 3. The two stunted plants in the foreground are showing symptoms of pineapple mealybug wilt disease.

Photo 4. Many plants with severe symptoms of pineapple mealybug wilt disease.

Common Name

Pineapple wilt

Scientific Name

Mealybug wilt of pineapple

Distribution

Worldwide; in all the major pineapple growing areas: Asia, Africa, South, North and Central America, the Caribbean, Oceania. In has been recorded from Australia, Cook Islands, Fiji. Plants from American Samoa and Samoa found to be infected for two pineapple mealybug wilt-associated viruses (PMWaVs) when maintained in the USDA-ARS National Clonal Germplasm Repository, Hilo, Hawaii.

Hosts

Pineapple and Pseudoananus. The latter is commonly called the false pineapple, not grown commercially (https://commons.wikimedia.org/wiki/File:Pseudoananas_sagenarius_(8400437895).jpg).

Symptoms & Life Cycle

Impact

Pineapple wilt occurs worldwide, is important, although often variable in plantations. This is because the disease depends on the presence of the virus(es), the number of mealybugs present, the length of time they feed, and the presence of ants. Trials in Hawaii showed that if pineapple wilt occurs during the first 3 months of the plant crop, average fruit weight is reduced by 55% compared to plants that remain virus free.

Detection & inspection

Look for early symptoms - reddening of leaves about halfway up the plant. Look for a change of colour from red to pink, a downward roll of the leaves and dieback of the tip as the leaves collapse. Look for Dysmicoccus mealybugs which spread the wilt disease.

Management

Management of pineapple wilt is difficult. It depends on at least four factors: i) clean (virus-free) planting material; ii) removal of weeds; iii) mealybug control; and iv) plant density.

NATURAL ENEMIES
There are a large number of predators and parasitoids of Dysmicoccus brevipes, including ladybird beetles, particularly Cryptolaemus species (see Fact Sheet no. 395), and wasps (encyrtids). In many countries, biological control is effective when ants (Pheidole, Iridomyrmex and Solenopsis) are controlled (see Fact Sheet nos. 361, 362&363).

QUARANTINE
Importation of pineapple plants for planting from countries where pineapple wilt occurs should not be permitted unless they are kept under observation in closed post-entry quarantine and tested for pineapple viruses (ampeloviruses and badnaviruses, in the Closteroviridae and Caulimoviridae families, respectively). For fresh fruit, an import risk analysis should be considered where countries are vulnerable to this serious disease, its mealybug vectors and associated ants. Conditions invariably require fresh pineapples to be de-crowned, from registered commercial plantations, fumigated pre-shipment, and inspected on arrival.   CULTURAL CONTROL
The control measures recommended below are for the control of the mealybug, and also for the control of Pineapple mealybug wilt-associated virus(es) that they are thought to spread.

Before planting:

• Use plants that have been treated to free them from virus (hot water or tissue culture) or selected from fields where the incidence of pineapple wilt is low:
  • Use plants grown from axillary or apical buds in tissue culture, and tested for the presence of Pineapple mealybug wilt-associated virus(es); OR
  • Hot water treatment. Place crowns or slips in water at 50°C for 30 mins. This has been used as a treatment to produce planting material free from Pineapple mealybug wilt-associated virus(es); OR
  • Use planting material from wilt-free areas or from fields where there is less than 10% of plants with pineapple wilt. Remove and destroy diseased plants before taking planting material. Additionally, do not take planting material from plants i) adjacent to those with pineapple wilt, or ii) that have recovered from symptoms.
  • Do not plant new pineapple crops next to those where pineapple wilt occurs. Never plant pineapples on land where the disease was present previously. If crops are heavily infested, remove and burn them, and plough the land, leaving it fallow until all the debris has been plough in or has decomposed.
• Cultivate the soil to destroy colonies of the big-headed ant (Pheidole); nests are near the soil surface, and re-invasion from surrounding areas is slow.
• Decide on plant density. Different bed configurations are used: single, two, or four rows and then a gap. Note, the higher the density (i.e., four adjacent rows before a gap) the easier it is for mealybugs to spread by leaf to leaf contact.

During growth:

• Remove plants with symptoms of pineapple wilt as soon as they are seen and burn them.
• Keep borders free from weeds that may harbour mealybugs and ants.

After harvest:

• Collect and burn all plant residues and, if practical, plough the land.

CHEMICAL CONTROL

• Dip crowns or slips in white oil or horticultural oil to rid the planting material of mealybugs.
• Use ant bait traps that are approved for use in pineapple to allow predators and parasitoids the opportunity to control the mealybugs naturally.
• If more than 3% of the plants have pineapple wilt (or mealybugs are common), use insecticides to control mealybugs and ants. Use diazinon or synthetic pyrethroids. (Note, diazinon is no longer registered in the EU; it is registered for use on pineapples in Australia).

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