Nematodes (Meloidogyne javanica and Pratylenchus brachyurus)

Root-knot nematodes (Meloidogyne javanica) cause distinct swellings (galls/knots) on the roots. The root lesion nematodes (Pratylenchus brachyurus) develop brown lesions (spots) on the roots, which may girdle the roots and cause their premature death.

The pineapple mealybug (Dysmicoccus brevipes)

The mealybugs are oval, pink in colour, up to 3 mm long, covered with a whitish waxy secretion, which develops into waxy filaments around the body. This mealybug is the most serious pest of pineapples, because it is a vector of the Mealybug or Pineapple Wilt Virus. The mealybug is common on the roots of pineapple and large colonies develop on the stems just above ground level.

The mealybugs may spread upwards to feed in the floral cavities, on both small and mature fruit, and on the crown leaves. Heavy infestations are conspicuous because of the white waxy adults, which often occur at the growing points, around the stem nodes, on the undersides of leaves, on the fruit and on the roots.

Feeding on leaves causes yellowing and drying up of the leaf-tips, which progresses towards the base of the leaves. Feeding in the blossom cavities causes wounds, which sometimes become contaminated by fungal spores resulting in a disorder called black spot. Feeding on roots is associated with the rotting of roots and subsequent wilting of the plant. "Smooth Cayenne" crowns used as planting material are frequently infested with mealybugs, and therefore new plantations usually become infested from the time of planting.

The bigheaded ant, Pheidole megacephala, is commonly associated with mealybug colonies. They do not attack the mealybugs but feed on the honeydew excreted by the mealybugs, preventing the formation of thick honeydew coats where crawlers (young mealybugs) may get entangled. Moreover, while feeding on honeydew, the ants interfere with the mealybug natural enemies. Thus, mealybug colonies thrive in presence of ants. Mealybug infestations may also be spread into new plantings by ants carrying the young mealybugs from one plant to another in their jaws.

Thrips (Thrips tabaci and Frankliniella schultzei )

Thrips are small (1.5 mm long), slender, brown insects with pale yellow hind wings that appear as a yellow line down the back of the body when the insect is at rest. Adult thrips have characteristic wings; the transparent wings have a fringe of hairs around the outside edge standing out in the same plane as the wing.

The onion thrips (Thrips tabaci) and the blossom or cotton bud thrips (Frankliniella schultzei) are considered important pests of pineapples because they are vectors of the yellow spot virus, which have been shown to be identical to the tomato spotted wilt virus. The blossom thrips feeds mainly on flowers and its feeding results in the development of "dead-eye" in the fruit. Thrips feeding on the crown of fruits results in concentric ring patterns developing on crown leaves.

Pineapple top and root rot (Phytophtora cinnamomi and P. nicotianae var. parasitica)

Top rot initially manifests in a colour change of heart leaves from green to yellow or light-brown with a red tinge. The leaf edges curve back and leaves are easily pulled out from the plant. Internally, the stem and leaf bases become soft, rotten and have an unpleasant smell. The growing point of the stem has a cheese-like appearance. Root rot causes similar symptoms like top rot. However, the outer leaves become limp and dieback from the tips. By this stage, the root system has rotten and plants can be easily pulled from the ground. Rot rot often extends through the stem to cause top rot. Fruits from diseased plants are normally small and are not marketable. Both P. cinnamomi and P. nicotianae var. parasitica are soil inhabitants and require water for spore production and infection. These fungi prefer wet soil conditions.

White leaf spot (Ceratocystis paradoxa, Thielaviopsis paradoxa)

The fungus Ceratocystis paradoxa causes white leaf spot, black rot, base or but rot and soft rot or water blisters. White leaf spots are yellow to brown and several centimetres long. Later they dry to become papery and straw coloured.

Base or but rot of pineapple is a common disease of crowns, slips and suckers used for establishing new plantings. Rot of planting material occurs when they are not dried and are packed with little aeration. The fungus also destroys older plants by entering through wounds caused in the collar region while weeding or other field operations. In severe conditions the entire plant may turn dark and rot within 2 or 3 days.

Black rot is a post-harvest disease occurring only on injured pineapple fruit. Only freshly cut or injured tissue is infected, and a soft black rot with dark coloured mycelium develops. Water blisters consist of a soft, watery rot of the fruit flesh with overlying skin glassy, water-soaked and brittle. Eventually, the skin, flesh and core disintegrate and the fruit dries out, leaving an empty fruit carcass containing a few, black vascular fibres. The fungus enters the fruit through wounds and the crevices between individual fruits.

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.

Yellow spot virus

The yellow spot virus has been shown to be identical to the tomato spotted wilt virus. It infects over a 100 species of plants including peppers, tomato, tobacco, eggplant, potato, broad bean, spinach, chicory and peas. A number of wild plants, including some common weeds such as the black jack (Bidens pilosa), Emilia sonchifolia and Datura stramonium, are also host of this virus.
Thrips are vectors of this virus. When host plants of the virus are grown near to pineapple plants, the incidence of the yellow spot virus is considerably enhanced due to thrips migrating into the pineapple field. Wind carries thrips long distances and thus also plays an important role in the transmission of the virus. One of the symptoms in the fruit is a blackened, dry cavity in the side of the fruit due to one or more "eyes" having died. This is known as "dead eye". Infection of very young fruit results in an irregular arrangement of fruitlets as some fail to develop. Attacked fruits may also fail to develop a crown. Thrips feeding on the crown of fruits results in concentric ring patterns developing on crown leaves. These spots enlarge and the infection spreads into the fruit itself, by which time the crown will often have dried out. The flesh of fruits thus infected will be discoloured and necrotic below the butt of the crown. The whole fruit may eventually become affected.