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Pests and Diseases

A general list of pests and diseases of the olive tree is provided. They are not all prevalent in all regions.

Nematodes

  • Several species of root lesion, citrus and root knot nematode can attack olive roots.
  • Nematode attack generally results in reduced vigour and possible stunting of trees.
  • Root knot nematodes cause the formation of galls or knots on the roots.
  • Testing soil samples from the proposed grove site for nematodes is recommended.
  • If root lesion, root knot or citrus nematodes are present, fumigation before planting will reduce the incidence of attack.
  • Nematodes cannot be completely eradicated over a large area and populations will rebuild.
  • Trees with healthy root systems have a better chance of resisting nematode attack.

Olive knot

  • Caused by a bacterium causing galls on twigs or branches at wounds.
  • Affects productivity by destroying twigs and branches.
  • Difficult to control, prevention of wounding is best strategy.
  • Careful pruning to remove galls is helpful.
  • Copper containing fungicides applied to wounds and scars are effective.
  • Application rates should be according to label recommendations.

Peacock Spot

  • Caused by a fungus, outbreaks are sporadic.
  • Lesions usually observed on upper leaf surface. Fruit can be attacked.
  • Small sooty splotches usually appear in winter and develop into greenish black circular spots.
  • Infection normally occurs in humid wintery conditions.
  • Most infected leaves will fall during summer.
  • Infected trees should be sprayed with copper-containing fungicide in late autumn.
  • Application rates should be according to label recommendations.

Phytophthora

  • Soil-born fungus that can cause root or collar rot.
  • Infected trees show reduced growth, have thin canopies, suffer from leaf dieback and eventually die.
  • Incidence is usually associated with poorly draining soils and prolonged periods of high soil moisture.
  • Water management is the basis for control.
  • Avoid spreading through contaminated implements and footwear.
  • Cropping history is also relevant as it is a pathogen of many crops.

Verticillium Wilt

  • Caused by a soil borne fungus
  • Leaves on branches die with the onset of warm summer weather.
  • Trees die after repeated attacks over several years.
  • Infection usually occurs in cool moist soil in late winter and spring.
  • No reliable methods of control have been developed.
  • Fumigation may be successful.
  • Pre-planting soil tests should be carried out to assess infection.
  • Cropping history is also relevant as it is a pathogen of many crops.
  • Avoid spreading through contaminated implements and footwear.

Olive Moth

  • Adult 6-8mm long, silvery grey coloured with small spots on wings.
  • Mature larvae pale brown to green with two greenish longitudinal and two yellow lateral stripes.
  • Life cycle involves several generations in a year, first feed on flowers, second feed on fruit and third on leaves.
  • Often lays eggs in prunings left in orchard.
  • Controlled by good orchard management and natural antagonists, or organic phosphate insecticides on first generation.

Olive Shoot Moth

  • Small white moth with mother of pearl glints, mature larvae dark green.
  • Active at dusk and night.
  • Bundles leaves together with silk-like threads to form cocoon.
  • Damages mainly young leaves by nibbling shoots.
  • Controlled with appropriate insecticides.

Olive Lace Bug

  • Sap-sucking insect that reduces vigour of trees.
  • Flat with lace-like wings and is no more than 2mm in length.
  • Resides on underside of leaves.
  • Causes rusty yellow spotting on top of leaves.
  • Control includes keeping trees healthy.
  • Chemical control with appropriate systemic insecticide.

Black Scale

  • Most common insect pest of Australian olives.
  • Brown black when mature, look like miniature tortoises, females have 'H' pattern on back.
  • Found on leaves and stems.
  • Cycle takes 4-8 months in southern States with 2-4 generations per year. Feed on sap of tree reducing fruit formation and causing leaf drop.
  • Predisposes tree to sooty mould which reduces photosynthesis and results in downgrading of fruit.
  • Natural predators of scale include wasps, ladybirds and lacewings.
  • Best controlled by minimising use of broad spectrum insecticides which kill scale predators.
  • Petroleum sprays can be used and are most effective against larvae, usually in late December and March/April.

Olive Scale

  • Similar to black scale but female is almost round and light to dark grey. Male is elongate, white and flat.
  • May attack fruit as well as leaves and stems.
  • Heavy infestations can cause defoliation and twig death, reducing productivity. Infested fruit becomes distorted.
  • Usually 2 generations a year.
  • Control similar to Black Scale.

Circulio Beetle (Apple Weevil)

  • Adult weevils about 9mm long, shiny, and coloured brown.
  • Shelter at base of tree during day then climb to feed on leaves at night.
  • Control includes barriers to stop beetles climbing trunk or chemical control using appropriate pyrethroid.

Cicada - infest trees and make herring-bone cuts in stems to lay eggs, causing damaged stems to die. Possible control with systemic sprays and pruning and burning infected branches.

Snails - can infest olive trees causing stress through defoliation and reduced photosynthesis. Generally in alkaline sandy soils high in calcium.

Birds - can cause considerable damage by snapping off branches, especially in young trees. Cockatoos, corellas and galahs appear to be main culprits. Control can be through planting more attractive trees around grove.

Hares - will occasionally nip off young stems and leave them on the ground. Tree guards will solve the problem.

Rabbits - may ringbark young trees. Tree guards will prevent this.

Wallabies - will sometimes eat leaves and young twigs, especially when there is a shortage of grass.

Kangaroos - will sometimes eat leaves and young twigs, especially when there is a shortage of grass. Damage not generally as severe as wallabies.

Sheep - can cause severe damage by eating bark.

Cattle - can break branches and eat lower foliage.

Horses - have been known to devour young olive trees.

 
 
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