Tea red spider mite

Key information

General comments

  • Caused by the mite Oligonychus coffeae.
  • Tea red spider mite only attacks the leaves and usually only becomes a problem through the overuse of insecticides, especially broad-spectrum insecticides such as pyrethroids that kill natural predators.
  • Some fungicides can also impact predatory mites.
  • Warm, dry conditions tend to favour the build-up of mite populations.

Identification

  • Eggs are pinkish red, nymphal stages are red and adults are dark red to almost black and about 0.5 mm long.
  • In severe infestations, the upper leaf surface becomes littered with the white cast skins of the mites.

Magnified image of red mites and their white cast skins.

Highly magnified image of tea red spider mites on a leaf

  • The main damage from mites is bronzing on the upper surfaces of older, more mature leaves.
  • When populations are very high, all the foliage on a tree may be bronzed and such extensive damage reduces photosynthesis.
  • The variety Wurtz is the most severely affected. Tea red spider mite damage can be confused with thrips damage.

Typical leaf bronzing caused by tea red spider mite

Treatment / Prevention

  • Regularly monitor the orchard so that action can be taken before the damage gets out of hand.
  • Also check for the presence of beneficial insects that attack tea red spider mite, these include: stethorus ladybird beetles, lacewing larvae and predatory mites.
  • Ensure that the infestation level is serious enough to warrant action.
  • 20% of leaves need to be affected to justify spraying.

Thrips – Greenhouse

Key information

Cause

  • The insect Heliothrips haemorroidalis.

General comments

  • Thrips can become a problem through overuse of insecticides, especially broad-spectrum insecticides such as pyrethroids.
  • Other outbreaks appear to be triggered by certain conditions, for example, milder seasons.
  • They feed on both leaves and fruit.
  • Although greenhouse thrips occur in all states, they are mainly a problem in south-west Western Australia where they occur on a range of other fruit crops such as nectarines, plums and citrus, as well as many ornamental shrubs.
  • They favour humid locations, trees along waterways and densely planted or overgrown trees. They are relatively weak flyers and often there is a resident population in a particular location that flares up from time to time.

Identification

  • Nymphs are slender, transparent green becoming black as they mature. Adults are also slender, about 1.5 mm long when mature and similar in size and appearance to red-banded thrips.
  • Greenhouse thrips are sap feeders with rasping mouthparts and commonly feed on the underside of leaves or where fruit touch.
  • Thrips are most active in warmer weather, with low activity during winter. Several generations can occur each season.

 

Highly magnified pictures of a transparent nymph (left) and dark coloured adult (right). (Photos – Alec McCarthy, DPIRD)

Magnified adults and nymphs. (Photo – Alec McCarthy, DPIRD)

  • Affected leaves acquire a pale silvery bronze appearance.

 

Silvery bronze leaf damage (Photo – Alec McCarthy, DPIRD)

  • Fruit has a muddy reddish brown colour and the skin can then become thick, hard and cracked, especially where fruit are touching.
  • Black specks of excrement may be noticeable wherever damage has occurred.

Severely affected fruit. (Photo – Alec McCarthy, DPIRD)

Treatment / Prevention

  • Where this pest is a known problem, monitoring should be conducted during the warmer months (November to February in Western Australia).
  • Pay particular attention to the underside of leaves and to fruit clusters, especially where fruit touch. Always check trees beside waterways and where flare-ups have occurred previously.
  • Greenhouse thrips will not normally be caught on sticky traps like other thrips species.
  • Parasitoids such as Thripobius semiluteus (a tiny wasp), may be useful in their control.
  • Damage is often minimal, and control is not warranted. If damaging populations are detected and natural control does not appear to be working, then an appropriate registered insecticide should be applied to the affected trees only.

 

Thrips – Red banded

Key information

General comments

  • Red-banded thrips, Selenothrips rubrocinctus, have only been recorded on avocados in coastal areas from the Queensland-New South Wales border and northwards.
  • They attack leaves and fruit of avocado but usually become a problem through the overuse of insecticides, especially broad-spectrum insecticides such as pyrethroids.

Identification

  • The nymphs are translucent yellow-cream; the first two segments of the abdomen are distinctly pigmented with red that forms a band around the body.
  • The adult thrips are about 1.3 mm long, black and have two pairs of narrow, feathery wings that fold along their back when at rest.
  • Red-banded thrips have rasping/sucking mouthparts designed to extract the contents of plant cells.

Magnification shows a black adult (top left) and several cream-coloured nymphs with a distinctive red band. The small, dark, spherical objects are thrips excreta.

  • Damage to leaves – feeding causes browning on the upper surface and an inward rolling of the leaves. Damage can be extensive, covering a large part of the canopy.

Browning on upper surface of leaves and inward rolling of affected leaves caused by red-banded thrips.

Severe infestations can result in the bronzing of leaves over a large part of the canopy.

  • Damage to fruit – feeding by red-banded thrips causes a bronzing of the skin and the surface becomes covered in their black excretory deposits. Affected fruit is downgraded.

 

Affected fruit (right) shows typical discolouration of the skin surface compared with unaffected fruit (left).

Treatment / Prevention 

  • Thrips damage is generally not serious enough to warrant special treatment as they are normally well controlled by beneficial insects.
  • The spray program for spotting bug will usually control thrips. Damage often goes unnoticed during the growing season and is not detected until harvest.
  • It is very difficult to discover thrips that may be causing extensive damage to pockets of fruit at the tops of trees or in secluded positions in heavily foliaged trees.
  • Best approach is to thoroughly check the orchard on a regular basis to pick up developing infestations on the more visible parts of trees. If damaging populations are detected an appropriate registered insecticide should be applied.

Tussock moth

Key information

General comments

  • The caterpillar of the moth Acyphas leucomelas and other species of the tussock moth family.
  • Tussock moth is an uncommon pest of avocados.

Identification

  • Caterpillars are distinctive, with long hairs protruding from the body.
  • They are often found between fruit that are touching.
  • Caterpillar feeding causes deep scarification of the fruit skin.

 

Three different species of tussock moth caterpillars are shown here.

Treatment / Prevention

  • Regular monitoring of the orchard for other pests will reveal damaging populations before severe damage occurs.
  • Usually pest numbers and damage are not serious enough to warrant special treatment.
  • The spray program applied for spotting bug and other pests will adequately control tussock moth.

 

Whitefly

Key information

Cause

  • An unknown species of the Aleyrodidae family.

General comments

  • The immature stages and adults of whitefly can damage leaves.
  • This pest has been recorded on avocados under conditions where natural predators have been suppressed by broad-spectrum insecticides.
  • They are more common in cooler regions

Identification

  • Whiteflies are not true flies but bugs that feed by sucking the sap from plants. The adults are small, mealy-white insects with transparent wings.

Magnified underside of leaf shows immature whiteflies.

  • They feed on the undersides of leaves, causing patchy, interveinal yellowing on the corresponding upper surface.

Whitefly attacks the lower surface of the leaf causing yellow mottling on the upper surface.

  • Feeding damage on new flush causes twisting and distortion of leaves.
  • Heavy populations of whitefly produce large quantities of honeydew, which lead to the growth of sooty mould and downgrade fruit.
  • Due to their relatively short life cycle, these pests multiply to form large populations very quickly.
  • Damage can be confused with the mottling and leaf distortion caused by zinc deficiency. The combined absence of whitefly insects, detritus and honeydew will distinguish zinc deficiency from whitefly damage.

Treatment / Prevention

  • Whiteflies are usually well controlled by beneficial insects and not serious enough to warrant treatment.
  • Avoid continuous use of broad spectrum insecticide sprays that are disruptive to beneficial insects.

Zebra shield bug

Key information

Cause

  • Zebra shield bug Bathrus variegatus.

General comments

  • This bug has only been a problem in orchards in the Blackbutt area of Queensland where their native plant hosts grow close to the affected orchards.
  • Although these bugs are common on the Queensland coast, they have not been recorded attacking coastal avocados.

Identification

  • Severe damage is caused to fruit, but the bugs are also capable of causing the death of branches (up to 100 mm in diameter) through their continuous, concentrated feeding in one spot on the branch.

 

Eggs laid on the underside of a leaf (left) and an adult zebra shield bug on an avocado fruit stalk (right).

  • Damage on younger green branches appears as white, dried sap and on older branches as large dark ‘dead’ patches.
  • Pathogenic fungi gain entry at these feeding sites, infecting the whole branch and killing it.
  • Damage to fruit produces white, powdery deposits and is difficult to differentiate from spotting bug and avocado fruit borer.

 

Zebra shield bug stings to fruit are often surrounded by dried white sap.

Treatment / Prevention

  • Monitor branches and fruit for damage. Sprays applied for spotting bug control may provide incidental control of this pest.

Treatment of Phytophthora root rot

 

Refer to the Manage Phytophthora Root Rot Poster. Phytophthora root rot requires an integrated approach, this is illustrated by the ‘Pegg Wheel’ on this poster.

 

Application of phosphorous acid –

Phosphorous acid has been extensively researched and proven to be an effective fungicide; however, the recommendations for its use should be strictly adhered to in order for it to be effective.

The whole aim of this treatment is to get sufficient phosphorous acid into the feeder roots in order to protect them from Phytophthora cinnamomi.

Considerable effort was made to provide the best and most up to date advice for the use of phosphorous acid in the video Protecting your avocado trees from Phytophthora root rot and the poster Manage Phytophthora Root Rot Poster. The poster has been updated twice since its original release.

There are two methods of application, injection and foliar spray, but the same timing applies to both.

Timing of phosphorous acid applications

  • The timing of any phosphorous acid application, injection or spray, is absolutely critical to achieve the necessary levels of phosphorous acid in the roots for protection.
  • The time to apply phosphorous acid is when root growth is taking place – this is when there is a net movement of sugars and other resources to the roots to fuel growth. Systemic chemicals such as phosphorous acid will flow there at this time too. When this is happening, the roots are said to be a strong “sink”.
  • There are two windows of opportunity for application (indicated by the red arrows in the growth cycle below):
    1. Short window – late spring when the spring leaf flush has fully grown and matured.
    2. Long window – autumn/early winter once the summer leaf flush has fully grown and matured, but no less than 6 weeks before flowering.

 

 

  • Applying at other times is ineffective and a waste of resources e.g. if applied during leaf flush or flowering, the phosphorous acid will end up in the leaves or flowers respectively, not the roots. Phytophthora cinnamomi does not infect leaves or flowers.
  • Application during the late spring window will result in some of the phosphorous acid going to the fruit because they are actively growing at this time, but if guidelines are followed MRLs in the fruit will not be exceeded.

 

Application of phosphorous acid by injection

  • Injection is suitable for both sick and healthy trees.
  • Prepare a 20% solution of phosphorous acid by diluting 1 part of a 600 g/L product (e.g. Agri-Fos 600) with two parts of water. Use a product that has been buffered to pH neutral.
  • Measure the diameter of the tree and multiply the diameter by 15 to work out the total volume to inject in the tree.

Example for a tree with a 4 metre diameter:

4 x 15mL = 60mL of solution per tree
  • Divide the total volume calculated per tree by 20 to determine how many separate injection sites to use per tree. In this example: 60mL ÷ 20 = 3 injection sites
  • Inject 20mL of solution into each injection site.
  • Distribute the injection sites evenly around the whole circumference of the trunk (roughly a handspan apart) in order to get protection for roots around the whole tree circumference (there is no lateral movement in avocado). Each injection will only protect the segment of the root system under it.
Space needles evenly around the circumference of the trunk, about a handspan apart. Each needle will only protect a wedge-shaped section of roots underneath it. No lateral distribution of fungicide takes place.

 

  • Do not use higher concentrations of phosphorous acid as a short cut to reduce the number of injection sites – since there is no lateral movement in avocado this would result in segments of the root system being unprotected.
  • In older trees it is OK to inject large limbs instead of the trunk but select limbs that are distributed around the whole circumference of the tree.

Tips for injecting phosphorous acid

  • Water trees the night before injecting to encourage good sap flow and start injecting as early as possible the next day. Uptake usually slows right down late morning (transpiration slows as the stomata close), when this happens stop injecting for the day and start again the following morning.
  • Do not inject at the points where branches join the main trunk nor immediately above or below previous injection holes.
  • Use a cordless drill and ensure that the drill bit is an appropriate size for the injection equipment being used. Drill injection holes about 25 – 50mm deep at a downward angle of about 45°. Carefully withdraw the drill so as not to enlarge the bore of the hole.
  • Draw 20mL of the phosphorous acid into the equipment then carefully and firmly screw the syringe tip into the drilled hole without enlarging the hole. A tight fit is necessary to ensure fungicide does not leak out the sides.
  • Do not apply excessive hydraulic pressure as this may separate the bark from the tree. With low-pressure injection systems, holes do not have to be plugged after injection. Where low pressure systems (such as veterinary syringes, Chemjet® or Aongatete Avo-Ject® syringes) are used, leave them in place till all the chemical has entered the tree, this should take about 15 to 30 minutes. If it takes longer it generally means that either the applicator has not been properly inserted or the tree is not transpiring sufficiently (stomata closed due to dry soil and/or high temperatures). Leave the injectors in place for longer and if necessary, check soil moisture is sufficient and try again early the next morning. Once all the phosphorous acid has been drawn into the tree remove the syringe by unscrewing it.

 

  • After treatment, flush all injection equipment with clean water to remove any chemical residues to prevent damage to rubber and plastic components.

 

Application of phosphorous acid by foliar spray

  • Foliar phosphorous acid sprays are only effective and recommended for healthy trees to maintain their protection. The compromised canopy of a sick trees is unable to absorb sufficient phosphorous acid so the tree must be injected instead.
  • Use a rate of 8.3 mL of a 600 g/L product per litre of water to produce a 0.5% solution of phosphorous acid (some of the older labels list a rate that gives a solution that it is only 0.17 to 0.2% which is ineffective).
  • It is important to ensure that the spray mixture in the tank has a pH close to neutral to avoid leaf burn. You need a pH testing kit (many growers use a swimming pool testing kit). To neutralise an acid mixture, it is safest to use potassium bicarbonate e.g. ‘Agri-K 415’ (not potassium or sodium hydroxide which are extremely caustic and dangerous to use). Add the potassium bicarbonate little by little, keep the spray tank agitator going and re-test frequently (it will get to a point when it changes quite quickly after a small addition of the neutralising product).
  • It is important to use sufficient spray volume to get enough chemical into the tree. For an orchard block of mature trees, you need at least 2,500 L/ha. Do not use wetting agents as they can lead to leaf burn.
  • Multiple sprays (about four) need to be applied to be equivalent to application by injection.

Tips for phosphorous acid sprays and why failures occur

  • Multiple sprays are required to be equivalent to one injection, be guided by root analysis results. It is much harder to lift the root phosphonate from a very low level but once concentrations are at or close to the desired level they take far fewer spray applications to maintain.
  • Use the correct rate: 8.3 mL of a 600 g/L product per litre of water to produce a 0.5% solution of phosphorous acid
  • Apply a spray volume of at least 2,500 L/ha per spray on a mature orchard to get enough phosphorous acid into the trees.
  • Correct timing is essential but is the same for both injection and spray methods.
  • Do not add wetters or stickers.
  • During hot weather, phosphorous acid sprays may react with copper fungicide residues (especially copper hydroxide products) on the leaves and cause leaf burn.

 

Testing phosphorous acid levels in the roots

  • Regular testing of the white feeder roots is highly recommended to guide phosphorous acid applications.
  • Timing:

◦ Spring – two weeks before spring leaf flush hardening (to determine if phosphorous acid needs to be applied in spring)
◦ Summer – two weeks before the start of autumn phosphorous applications (to guide applications)
◦ Late autumn/early winter – four weeks after autumn application (to see if target levels have been achieved or if more needs to be applied)

  • Collect 5 grams of white feeder roots per sample. Access the two necessary forms by clicking here and answer all the questions, the more complete your answers the more reliable will be the recommendations from the interpretation. Send the root sample and the two completed forms to: MA Analytical Services P.O. Box 3104 Tarragindi Qld 4121
  • Levels need to be maintained above 80 mg/kg for the whole season to protect the roots, however since levels decline naturally during the season (this is particularly rapid in the warmer, wetter regions such as in North Queensland) this means achieving much higher starting levels by the end of the main application period of autumn/winter (make sure all applications cease at least six weeks before flowering).
  • At the end of the autumn/winter application window aim for a root level of >200 mg/kg.
  • If levels are above 150 mg/kg prior to the spring application window then an application at this time is not required, unless your farm is in North Queensland in which case both spring and autumn applications should be applied (levels decline more rapidly in this environment).
  • For further detail about the testing service please contact Graeme Thomas, GLT Horticultural Services: 0419 977 267 or email: glthort@bigpond.com.

 

Use of metalaxyl

This fungicide acts directly on Phytophthora in the soil and will kill some but not all the Phytophthora inoculum in soil. It is also taken up by the roots, acts systemically to have curative properties. Trade names include Medley®, Ridomil Gold® and Zeemil®.

  • Newly planted trees and older badly affected trees can be treated by spreading metalaxyl on the soil surface under the canopy and lightly watering it in. It is not likely to be cost effective for treating a large number of declining trees.
  • Follow the label rate and instructions.
  • Metalaxyl is effective for the first one or two applications but the response from subsequent applications is less beneficial because micro-organisms that degrade it build up in the soil.
  • It is leached from the root zone by heavy rain or irrigation.

 

Phytophthora trunk canker

Cause:

The soil-borne water mould Phytophthora cinnamomi.

General comments:

Tends to be isolated to a few trees here and there, for example, when irrigation sprinklers are placed too close to the trunk, the trunk has been damaged, or there has been a cyclone. It has occurred in Hass on Mexican race rootstocks in North Queensland following cyclones, where very wet conditions were combined with physical damage to the tree trunk from flying debris.

Identification:

The canker appears as a dark brown water-soaked area on the bark. Healthy bark is normally a grey-brown colour. A white secretion of dried sap is usually evident within the affected area; however, the presence of the white secretion alone does not necessarily indicate trunk canker disease (chronic boron deficiency and injury to the trunk may produce the same symptom). After some time the affected section ‘sinks’ into the trunk.

   

Active trunk cankers bleed sap that dries to form a white powder.

Lesions, splits and sunken areas on the trunk from older infections.

Treatment/prevention:

Using a sharp knife, pare away all the diseased bark and wood and paint the area with a mixture of a copper fungicide and water-based paint. Alternatively, spray affected trunks with a registered phosphonate fungicide. Protect the trunk from physical damage to prevent the pathogen from gaining entry. Avoid continuous wetness of the trunk from sprinklers or from having mulch material against the trunk.

Crop Cycle Calendars

Crop cycle calendars have been prepared for each of the main production regions of Australia.

Please click on “Related Resources” above to view all Crop Cycle Calendars.

These calendars are intended to give the grower a guide to the main management practices, such as pest and disease control, due at different times in the seasonal crop cycle. Further detail about each practice can be found in other sections of the Best Practice Resource. Growers can use the calendars as memory joggers for what needs to be undertaken in the orchard at different times of the year. Please be aware that variations occur between seasons and between localities within each region so growers need to exercise judgment in following the timing suggested. Management activities should be linked to events in the crop cycle rather than to the month of the year.

Avocado Canopy Management Summit 2022

 

The Avocado industry development and extension (AV17005) project team conducted a major study into avocado canopy management in 2022. A summit was held in Brisbane in September 2022 with experienced avocado growers and consultants aiming to reassess and update current best practice, identify research gaps, and highlight regional extension needs on behalf of the Australian avocado industry.

The resources include:

» Domestic guest speakers

» International guest speakers

Keynote speakers

Francisco Mena

Francisco is based near Santiago in Chile and runs a consultancy company called GAMA Ltda which also conducts research. He consults internationally, regularly present results of research at the World Avocado Congresses and is considered to be a leader in avocado canopy management.

Bram Snijder

Bram is based in Tzaneen in South Africa and is highly regarded horticultural consultant. He has worked as a Scientific Researcher in avocado and coffee for over 20 years for the Agricultural Research Council in South Africa and now runs his own private consultancy
business.

Colin Partridge

Colin is a technical support to Avoco and consultant in New Zealand. He grew up in South Africa and has worked as the Managing Director for the South Africa Avocado Growers’ Association and was on the committee that organised the first World Avocado Congress in South Africa in 1987.

More information

DAF: Bridie Carr, bridie.carr@daf.qld.gov.au or 0436 675 740

This event was part of the strategic levy investment project, Avocado industry development and extension (AV17005), part of the Hort Innovation Avocado Fund. This project has been funded by Hort Innovation, using the Hort Innovation avocado research and development levy, co-investment from the Queensland Department of Agriculture and Fisheries, and contributions from the Australian Government. Hort Innovation is the grower-owned, not-for-profit research and development corporation for Australian horticulture.