Citrus Pests, Diseases & Disorders

CITRUS PESTS, DISEASES & DISORDERS

There are a myriad of pests, diseases and disorders, which infest Citrus in Australia.

Listed below are pests, diseases and disorders found on Citrus, on the following pages, you will find a description of some species, damage caused, monitoring and control measures.

Pests of citrus

·  Citrus aphids

·  Citrus leafminer

·  Cottony cushion scale

·  Crusader bug

·  Fuller's rose weevil

·  Identification of thrips in citrus

·  Katydid

·  Light brown apple moth in citrus

·  Long tailed mealy bug

·  Queensland fruit fly in citrus

·  Mite pests of citrus

·  Pezothrips

·  Red scale

·  Spined citrus bug

·  Thrips: Identification of thrips in citrus

Diseases of citrus

·  Armillaria root rot of citrus trees

·  Citrus blast

·  Citrus canker

·  Citrus exocortis

·  Lemon scab in citrus

·  Melanose in citrus

·  Septoria spot in citrus

·  Sooty blotch of citrus

·  Sudden death in citrus

For more information, see the Agfacts and Primefacts documents, located on the wikispace you downloaded this information from.

You may also visit the NSW Department of Primary Industries website.
Aphids

Several species of aphids are found on citrus:

·  brown citrus aphid

·  black citrus aphid

·  melon aphid

·  spiraea aphid.

Description

·  Aphids are small (about 2 mm long), soft-bodied insects with characteristic tubular extensions to the abdomen.

·  They feed on plant sap using their sucking mouthparts.

·  Aphids have complex life cycles.

·  Adults can be winged or unwinged and females can reproduce with or without mating.

·  Aphids can build up large populations within a short period of time. However, in environments undisrupted by pesticide use, aphids are normally kept at low levels by a suite of beneficial insects.

Damage

·  Feeding by aphids distorts shoots and can transmit plant viruses.

·  They produce honeydew, which encourages the growth of sooty mould.

Monitoring

·  Randomly check young shoots in early September and late October for spring flush, and February to April for summer–autumn flush.

·  Check randomly selected young shoots, and examine five to ten young leaves from each shoot for the presence of aphids, honeydew and sooty mould.

Natural enemies

·  Parasitic wasps

·  Predatory lady beetles

·  Lacewings

·  Syrphid flies

Control measures

·  Control action is needed only when 25% or more of leaf flushes are infested and when the presence of beneficial insects on infested shoots is less than 25%.

·  Appropriate actions include spraying young growth with a specific aphicide.

Cottony Cushion Scale.

Description

·  10–15 mm long.

·  The complete life cycle of cottony cushion scale takes around 2 months in summer, with at least two generations occurring per year.

·  The female cottony cushion scale produces up to 1000 eggs, which are carried in the fluted white cottony egg sac

Damage

·  The honeydew encourages the growth of sooty mould, which downgrades fruit quality and, in severe infestations, causes leaf drop, twig dieback and deterioration of tree health.

Monitoring

·  Monitoring is needed most during February–March. Check five randomly selected green twigs per tree and examine each twig for the presence of adult scales with egg sac.

·  If 5% of the green twigs checked are infested with one or more scales, then actions should be taken.

Natural enemies

·  Ladybirds

·  Lacewings

Control measures

·  Appropriate actions include spraying petroleum spray oils (PSOs), which are best applied when crawlers are most active soon after hatching (around mid to late March).

Crusader Bug

Description

·  The adults are brown and have a distinguishing yellow X-shaped cross. Juveniles do not have a cross — they have two small spots on their back.

·  Approximately 2.5 cm long.

·  Three to four generations per year.

·  Five nymphal stages.

·  Eggs are large, elongated and brown, with a rounded lid.

Damage

·  Crusader bugs feed on young plant growth, resulting in the wilting of shoots. The shoots go brown and often die back to the old wood.

·  All citrus varieties can be attacked.

Monitoring

·  Monitor once or twice during October–April by checking five randomly selected shoots on each tree.

Natural enemies

·  Assassin bugs

·  Praying mantises

·  Birds

·  Parasitic wasps

Control measures

·  If 25 or more of the shoots are infested, spot spray with a selective insecticide.

Fullers Rose Weevil

Description

·  Adult fuller's rose weevils are wingless, grey-brown, and about 8 mm long.

·  Mature larvae are legless, yellow and about 6 mm long.

·  Females produce eggs glued together in yellowish, papery masses of about 20-30 without mating.

·  Eggs are laid under fruit calyces, in bark crevices, or in microsprinklers under the tree.

·  After hatching, the larvae drop to into soil and feed on citrus roots.

·  Adults then emerge from the soil mostly between February and May. They climb trees via trunks, weeds and low-hanging foliage.

·  The adults chew leaf margins, leaving a serrated edge.

·  Foliage near the trunk or touching the ground is most likely to be damaged.

·  There are 1-2 generations per year.

·  Adults can be found all year, but peak levels are from February to May.

Monitoring

·  Fortnightly monitoring is necessary from early August to late October, and again from February to late June.

·  Trees selected for monitoring must be randomly scattered throughout the block.

·  Examine low-hanging fruits near the trunk, looking for egg masses under the calyx.

·  Examine low-hanging foliage for signs of feeding damage.

·  The abundance of adult weevils can be monitored by beating tree limbs.

Natural enemies

·  Wasp Fidiobia citri

·  Assassin bug

·  Praying mantises

·  Parasitic nematodes (such as Heterorhabditis sp.)

Control measures

·  Control of Fuller's rose weevil is required especially for exporting crops.

·  Appropriate actions include pruning the skirts of trees at the end of each season, controlling weeds, and applying sticky bands around the tree trunk.

Damage

Katydid

Description

·  Grasshopper-like insects with thin, long antennae (usually longer than body).

·  There are three species of katydid in Australia:

o  citrus katydid

o  inland katydid

o  spotted katydid.

·  Adults are green to brown, and 40–50 mm long.

·  There is one generation per year.

·  Eggs are laid from January to April.

·  Nymphs hatch in early spring and develop through five stages.

·  Adult stage is reached during December–January.

Damage

Deep chalk-like scars on the fruit surface

·  Nymphs and adults feed on citrus flowers, fruits and leaves.

·  Feeding on fruits results in fruit drop or deep chalk-like scars on the fruit surface (see image).

·  Damage is more common in oranges than in lemons, grapefruit or mandarins.

Natural enemies

·  Parasites: an unidentified tachinid fly species, and an unidentified wasp species.

·  Predators: assassin bug, praying mantises, sphecid wasps, and birds.

Monitoring

·  Monitor every 2 weeks from mid-September to late November.

·  On each occasion, check five randomly selected fruits from each of five randomly selected trees.

·  Use sticky trunk bands to monitor the numbers of emerging nymphs.

Control measures

·  Action should be taken when 5% or more fruits are showing fresh injury, or when sticky bands have more than two emerging nymphs per tree.

·  Use a selective insecticide in areas of the orchard where the action threshold is exceeded.

Long Tailed Mealy Bug

Description

·  Adults are 3-4mm long with mealy wax cover and long tail filaments (as long as or longer than the body). When squashed, the body fluids are seen to be pale yellow.

·  The female produces around 200 live young (which she deposits under her body) over a 2–3week period.

·  During summer the life cycle is completed in around 6weeks (about 12weeks in winter).

·  There are three to four generations per year in NSW, VIC and SA.

Damage

·  The honeydew produced by mealybugs encourages the growth of sooty mould, which downgrades fruit quality, and in severe cases lowers general tree health. Mealybugs are often found in sheltered sites.

Sooty mould

Monitoring

·  Fortnightly monitoring is critically important in November–December.

·  Check five fruit per tree from ten randomly selected trees throughout the block.

·  Examine under the fruit calyx and, in autumn, check the navels of navel oranges.

Natural enemies

·  parasitic wasps

·  lacewings

·  ladybirds

Control measures

·  In navel oranges and grapefruit, action should be taken when 10% or more of the fruits are infested with mealybugs. Action level is 20% for all other varieties. In late November and early December, control is required if the action level is reached before calyx closure.

·  Chemical control measures include petroleum spray oils (PSOs) (or PSO and a compatible pesticide) and soap sprays.

Pezothrips

There are several species of thrips found in citrus. Of these, Pezothrips kellyanus (Kelly’s thrip) is of particular concern. It is a major pest in the Riverland and Sunraysia. All citrus varieties can be attacked, but lemons are particularly susceptible.

Description

·  Adult pezothrips are black, and 2–3mm long.

·  The life cycle consists of eggs, two larval stages, pre-pupa, pupa and adult.

·  There are about six generations per year.

Damage

·  Pezothrips feed on young tissue, particularly near the calyx, producing a circular stem-end scar (halo).

Monitoring

·  Check for pezothrips in spring and autumn.

Natural enemies

·  Some parasitic wasps.

Control measures

·  Control measures are needed when 5% or more young fruits, or 10% or more maturing fruits, are infested. Pezothrips can be controlled with chlorpyrifos or methamidophos. However, both chemicals are quite disruptive to IPM programs. Avoid using them unless absolutely necessary.

Red Scale

Red scale is the most widespread pest of citrus in New South Wales.

Description

·  Females have four, and males five, development stages.

·  All stages are sessile (non-free-moving) except the early part of the first stage (crawlers) and adult males (winged).

·  The scale cover of the female is circular (about 2mm diameter), whereas that of the male is elongated.

·  The colour of the scale cover changes from white in the first stage to reddish brown in later stages.

·  Depending on temperature, red scale has two to five generations per year in NSW.

Damage

·  It infests leaves, fruits, twigs and limbs of all varieties of citrus.

Monitoring

·  Check five fruits per tree during October–March.

Natural enemies

·  Aphytis wasp

·  Ladybirds

·  Chilocorus

·  Predatory mites

Control measures

·  Take appropriate actions if 10% or more of fruits of early varieties are infested, or 15–20% or more of later varieties are infested. Appropriate actions include releasing parasitic wasps and the application of petroleum spray oil.

·  When choosing the latter option, time the spray when young scales are predominant.