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GREEN COFFEE AND THE DREADED GREEN SCALE

Green Coffee Scale in coffee

Bruno Pinese, Harry Fay & Rod Elder, Department of Primary Industries and Fisheries.

Coffee- Green coffee scale (Coccus viridis) on the back of a leaf. Note the black sooty mould

Green coffee scale (Coccus viridis) on the back of a leaf. Note the black sooty mould

Description

Adult

The adult female of green coffee scale is oval to elongate in shape, with a flattened profile. It is pale yellow-green in colour, and 3-4 mm long. The roughly U-shaped gut is visible through the partially transparent top of the scale as a line of black spots. At the anterior (head) end, there are distinctive black eye spots. The scales have antennae and well-developed legs and, unlike most scales, can move slowly around the host plant. These features can be used to distinguish the scale from other soft scales such as soft brown scale.

Immature stages

Eggs are not seen as they hatch within the female or immediately after laying. Immature scales are similar to the adult female although smaller.

Life history

The females reproduce without mating. The life cycle takes 6-9 weeks and there may be 3-4 generations per year.

Distribution

Green coffee scale occurs from just south of Brisbane to north of Mareeba.

Host range

Longans, coffee, citrus and a wide range of other hosts including the ornamentals such as gardenia and ixora.

Management

Importance

Major and sporadic; potentially serious in coastal areas and occurrence is increasing in sub coastal areas.

Damage

This insect damages coffee by infesting leaves, twigs and fruit, sucking sap and secreting sugary excreta on which sooty moulds thrive.

Action level

Monitor for green coffee scale together with other soft scales once or twice from mid-October to mid-November. Sample 25 leaves from each of 20 randomly selected trees per 1 to 5 ha block. Apply spray if 10 or more leaves are infested with 1 or more scales. Use oil where Integrated Pest Management (IPM) is practised and direct the spray at young scales during early November.

Control methods

Biological

There are one or two small parasitic wasps, eg. Coccophagus rusti and Encarsia sp. that periodically cause significant mortality of the scale. The Kenyan wasp Diversinervus stramineus has been released on coffee in North Queensland. Its effectiveness is yet to be determined. Ants attend the scale for their honeydew and in so doing disturb potential scale parasitoids. When the ants are controlled, scale numbers drop dramatically.

The mealy bug predator (Cryptolaemus montrouzieri) preys on green coffee scale.

The fungus Verticillium lecanii can cause up to 90% mortality of the scale during wet weather in late summer to autumn, particularly when populations of the scale are large.

Chemical

Good coverage is important when applying oil to control scales as they are sedentary.

Recommended chemical

Petroleum oil (narrow range), methidathion (in non-bearing plants only). Good coverage using high volume sprays is important when applying oil to control scales.

Chlorpyrifos on the soil around the base of the trunk for ants.

Ants are attracted to and feed on the honey-dew produced by the scales. They disrupt natural enemies of the scale and should be controlled by spraying the soil round the trunk with chlorpyrifos or banding with tanglefoot. Some ants are predatory on cicada nymphs and their control may lead to cicada problems.

Note: This information was correct at the time of publication. However, it is the user’s responsibility to ensure that registered agricultural chemicals are used in accordance with legal requirements. (See Further information).

Always read the label.


October 7th, 2010
Topic: AGRICULTURE, FOOD DRINK, FRUIT VEG SMALL CROPS, PESTS DISEASES BACTERIA VIRUSES, PLANTS CROPS WEEDS Tags: , , , , ,

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