Mealybug or pineapple wilt virus
Infected plants become yellowish-red to bright red at the leaf tips, this colouration spreading down the leaf with time. Soon other leaves turn colour and also show signs of wilting. However, the inner heartleaves remain normal. Severely infected plants become stunted and produce small, undergrade and immature fruits. The first effect of the disease usually appears in the roots, which stop growing, collapse and then rot; this results in leaves symptoms similar to the effect of drought. The root system collapses and rots before the first leaf symptoms appear.
The disease is probably introduced with planting material, which may not show obvious disease symptoms. Once established, it is spread by mealybugs, sedentary insects, which are moved from plant to plant by attendant ants. The mealybugs are found at the base of leaves, moving on to healthy plants once their host starts to wilt.
Warm weather favours the build-up of mealybugs and this is when most serious outbreaks of the disease occur. Plants growing vigorously as on virgin land and well-fertilised soil (especially with nitrogen fertiliser) appear to be more resistant to wilt. Adverse growing conditions increase the susceptibility of plants to wilt. Plants may recover from wilt to different degrees, depending on the extent of the wilt and the age of the plant at the time of wilting; younger plants stand a better chance of recovery. Older plants are less susceptible than younger plants, and slips and suckers less susceptible than the mother plant on which they are borne.
- Use planting material from wilt-free areas.
- Control mealybugs. For more information on mealybugs click here
- In Hawaii, heating pineapple crowns in a large water bath at 50°C for 30 minutes permitted 100% plant survival and rendered 100% of the plants free of pineapple wilt-associated-virus. Growth of the heat-treated plants is more rapid than in non-heat-treated plants. The heat-treated plants are not readily colonised by mealybugs, nor do they show mealybug wilt even after more than two years from being planted in a commercial crop with severe mealybug wilt (Ullman et al., 1993).
- Plant resistant varieties if available. Some varieties of pineapple are more resistant to the virus than others, the variety "Cayenne and 'Masmerah' being highly susceptible. 'Singapore Spanish' shows some resistance.