Anthracnose (Colletotrichum gloeosporioides)

This fungal disease is primarily a post-harvest problem when fruit is at maturity stage. Infection takes place when fruit is still very young and the fungus stays dormant till the fruit ripens. The disease appears as depressed spots on the fruit and the spots are manifested as a rot, which can penetrate deep into the flesh. In wet weather, the spots may be covered with mass of slimy, salmon pink fungal spore mass. The disease may develop very rapidly in storage if conditions in storage are humid and warm.

The anthracnose fungus lives saprophytically on twigs, rotten fallen fruits and dead or dying infected leaves. The fungus is spread by water splash.

Avocado root rot (Phytophthora cinnamomi)

This disease can attack trees of any size and age. Leaves of infected trees are small, usually pale or yellow green, are often wilted and fall prematurely giving the tree sparse appearance. In advanced stages of the disease, branches die-back and fruit remains small and crop yield drastically reduced. Feeder roots get blackened, decayed and died. Infected trees die prematurely. The disease is prone in areas subject to flooding and in poorly drained soils. The fungus can be spread or introduced to new areas by use of infected seeds, infested soil, irrigation water containing spores of the fungus and infected seedlings. The host range of the fungus includes Acacia, Camellia, Casuarina, Cypress, Eucalyptus and Grevillea.

Cercospora fruit spot (Pseudocercospora purpurea)

The disease is primarily a problem to quality of fruits. The severity of infection varies from season to season and can cause losses of up to 60%. The lesions appear as small light-yellow spots on fruits and leaves. They later become reddish brown and eventually become hard and crack. Mature fruits are resistant. The disease development is favoured by humid conditions and high temperatures. The fungus is essentially spread by water splash and its spores are also wind-borne.

Bugs (Coconut bugs, Helopeltis bugs, stink bugs)

Adult coconut bugs (Pseudotheraptus wayi) are brown in colour and 10 to 15 mm long. Nymphs are red brown to green brown in colour and have long antenna. The adults and nymphs of the coconut bug feed on young and mature avocado fruit. Bug feeding causes necrotic bruise-like depressions. A hard lump develops, which can be easily removed when the fruit is peeled.

Helopeltis bugs also known as tea mosquito or mired bug are slender, delicate bugs, about 7- 10 mm long and have long legs and antenna. The females are red and the males are brown to yellowish red. The bugs prefer to feed on young plant tissue piercing the shoots, stems, leaves peduncles, petioles and fruits. Their feeding causes brown necrotic patches. Attacked leaves present angular lesion, which often drop out leaving holes as it attacked by biting insects. Feeding on young shoots causes dieback of the shoots. Feeding on fruits causes first a dark water-soaked mark around the feeding puncture, turning into a lesion with a light brown centre and black edge. The fruit may exude sap that forms a whitish deposit as it dries.

Stink bugs are shield-shaped bugs variable in size (6 to 15 mm long) and colour (green to brown or reddish brown). They emit a characteristic unpleasant odour when disturbed. They usually feed on the developing fruit. The feeding punctures cause local necrosis resulting in fruit spotting, and deformation.

False codling moth (Cryptophlebia leucotreta)

The false codling moth is small (wingspan of 16-20 mm), dark brown to grey in colour. The moths are active at night. Female moths lay single eggs mostly on the fruit. After emerging from the egg, the young caterpillar tunnels into the fruit and the fruit sap thus liberated forms a typical white crystalline excrescence on the surface of the fruit. When moths lay eggs on young fruits the caterpillars usually die and thus large caterpillars are seldom found.

However, the caterpillars are able to develop if fruits are approaching maturity when infested. The young caterpillar is creamy-white with a dark brownish head. With age the body turns pinkish red. The fully-grown caterpillar is 15 to 20 mm in length. When mature the caterpillar leaves the fruit and pupates in the soil or beneath surface debris.

Fruit flies

Avocados, especially thin-skinned varieties might be attacked by various species of fruit flies. Some fruit flies lay eggs under the skin of the fruit that is just beginning to ripen, but others attack young and old fruit. When the fruit reaches about the size of a golf ball a sting lesion appears as a slight puncture mark surrounded by a white exudate. As the fruit develops the lesion becomes dry and turn into distinct star-shaped crack on the skin surface.

Scab (Sphaceloma perseae)

The fungus readily infects young, succulent tissues of leaves, twigs and fruits. Lesions appear as small dark spots, slightly raised, oval to elongated. These spots join up, giving a corky appearance to the surface of the fruits, impairing the appearance but not the internal quality of the fruit. Fruits are only susceptible when young until about half size development. The fungus requires moist conditions for sporulation and infection.

Scales

Scales are small, stationary brown greenish insects occasionally found sucking sap from avocado leaves. Soft scales such as Coccus spp. excrete large amount of honeydew, which lead to the development of sooty mould on leaves, branches and fruit. Honeydew attracts ants, which while feeding on the honeydew protect scales from natural enemies.

Armoured scales such as the coconut scale (Aspidiotus destructor) may encrust young twigs, leaves and fruit. They do not produce honeydew. Scales are usually not a problem in avocado orchards; however, damage can be serious on young tress and small twigs may be killed. Although the presence of scales on the skin of fruit does not cause internal damage, it may lead to rejection of fruit, especially if grown for export.

Spider mites (Oligonychus spp.)

Attack by spider mites (Oligonychus spp.) produce circular necrotic spots covered by dense webbing. As mite populations increase feeding causes leaf drop. These mites are more damaging to 'Haas' variety; 'Fuerte' variety is less affected.

Feeding by broad mites (Polyphagotarsonemus latus) causes leaf distortion. These tiny mites (0.1-0.2 mm long) cannot be seen with the naked eye, and are even difficult to detect with a hand lens. An attack by the broad mites can be detected by the symptoms of damage. Their feeding produces discolouration, necrosis and deformation of tissues.

Thrips (e.g. the black tea thrips Heliothrips haemorrhoidalis and the red banded thrips Selenothrips rubrocinctus)

Thrips are small, slender insects (1-2 mm long) with two pairs of fringed wings. Adult thrips attacking avocado are dark brown or black, and the immature stages are yellow in colour. The red-banded thrips can be distinguished by a bright red band across the abdomen of immature thrips.

Thrips are sometimes troublesome pests in avocado. They may cause damage to the leaves and fruit. Affected parts become whitish or silvery and are usually covered by dark-coloured droppings.

On fruit, feeding begins near the calyx, gradually producing a scar that can cover the whole fruit. Attacked fruits develop a leathery brown skin. Feeding is most common on young fruit; economic damage generally occurs on fruit up to 2 cm in length (2-3 weeks after fruit set). Older fruit with thicker skin is less susceptible to attack.