pests diseases of grasstrees

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7/28/2019 Pests Diseases of Grasstrees http://slidepdf.com/reader/full/pests-diseases-of-grasstrees 1/4 For more inormation visit www.agric.wa.gov.au The Chie Executive Ofcer o the Department o Agriculture and Food and the State o Western Australia accept no liability whatsoever by reason o negligence or otherwise arising rom the use or release o this inormation or any part o it.  Important disclaimer Department of Agriculture and Food Grass tree (  Xanthorrhoea preissii  ) The harvesting o grass trees or landscaping has become very popular in recent times as these unique specimens compliment both ormal and inormal gardens. The common grass tree  Xanthorrhoea preissii  ) is endemic to Western  Australia and grows naturally in sand, loam or gravelly soils to a height o our metres. They have a liespan o up to 600 years with a growth rate o only 1–2 cm per year. Under the Environment Protection and Biodiversity Conservation Act 1999 (the EPBC Act), it is an oence to take native vegetation including grass trees rom public lands or state orests. Permits are required or commercial salvaging where the site has been approved or urban or industrial development. Land owners wishing to harvest grass trees rom their property, must comply with State and Commonwealth legislation. Pests and diseases of grass trees By Christine Castalanelli and Harald Hoffmann, Biosecurity Communications; Marc Widmer Entomology  and Peter Wood Plant Pathology Note: 425  April 2010

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Page 1: Pests Diseases of Grasstrees

7/28/2019 Pests Diseases of Grasstrees

http://slidepdf.com/reader/full/pests-diseases-of-grasstrees 1/4

For more inormation visit www.agric.wa.gov.au

The Chie Executive Ofcer o the Department o Agriculture and Food and the State o Western Australia accept no liability

whatsoever by reason o negligence or otherwise arising rom the use or release o this inormation or any part o it.

 Important disclaimer

Department ofAgriculture and Food

Grass tree (  Xanthorrhoea preissii )

The harvesting o grass trees or landscapinghas become very popular in recent times asthese unique specimens compliment both ormaland inormal gardens. The common grass tree(  Xanthorrhoea preissii  ) is endemic to Western Australia and grows naturally in sand, loam orgravelly soils to a height o our metres. They havea liespan o up to 600 years with a growth rate

o only 1–2 cm per year. Under the Environment 

Protection and Biodiversity Conservation Act 1999 (the EPBC Act), it is an oence to takenative vegetation including grass trees rom publiclands or state orests. Permits are required orcommercial salvaging where the site has beenapproved or urban or industrial development.Land owners wishing to harvest grass treesrom their property, must comply with State and

Commonwealth legislation.

Pests and diseases of grass treesBy Christine Castalanelli and Harald Hoffmann, Biosecurity Communications; Marc Widmer Entomology  and Peter Wood Plant Pathology 

Note: 425 April 2010

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Structure

The trunk is composed o a mass o old lea basesheld together by natural resin which can take 10years beore it begins to orm. The centre o thetrunk is flled with a fbrous material. The needle likeoliage reduces moisture loss during periods o hotweather which makes the tree drought resistant.

The root system is shallow with the main purposebeing or anchorage. Surrounding the roots aremicrobes called mycorrhiza ungi which areessential or nutrient uptake in defcient soils andalso protect roots against some pathogen ungi.

Common pests

Scale

Scale insects are sap-suckers which have eithera waxy or armoured covering. Juvenile scales(crawlers) disperse to avourable sites on the leaand start eeding. The crawlers eventually becomeimmobile, and start building their protectivecovers, but are still sucking the needles. Thisactivity, i let unchecked, may eventually kill the

grass tree. Control scale with an application owhite oil, but not during hot weather as this mayburn the plant.

Mealybugs

Mealybugs oten have a number o overlappinggenerations per year. Their development isdependent on temperatures above 25°C with high

humidity. Ater hatching, the juveniles (crawlers)search or suitable eeding sites in shelteredareas. Control is best achieved in late October atcrawler stage with a systemic insecticide suchas Imidacloprid. Populations reach peaks duringspring and autumn.

Bardi grubs ( Bardistus cibarius )

The term ‘Bardi grub’ is used to describe the larvao the Longicorn beetle ( Bardistus cibarius ) , butmay also apply to other native boring larvae. A decaying trunk or a thick ‘skirt’ o dead oliageprovides the perect environment or attack bythese native borers and wood boring moths. Theemale moth lays her eggs into this oliage andthe emerging grubs bore their way into the fbrous

Mussel scale on Xanthorrhoea

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centre o the tree. This damage disrupts the tissuethat carries water and nutrients to the crown. Insevere inestations the tree will rot and all over.There is no registered chemical control, but burningo excess oliage (thatch) every 3–4 years will makethis an unsuitable haven or pests. Burning o doeslittle damage to the green crown, as it actually

promotes growth as it would in a natural fre.

Common diseases

Root DiseaseRoot rot (  Phytophthora cinnamonni  )

This ungal pathogen causes the roots to rot,preventing the grass tree to take up water andnutrients. It is usually present in damp or poorlydrained soils but will also survive drought. Asa result the central leaves wilt and turn brown,causing the crown to collapse and the trunk to rot.

Phosphorous acid sprays can be applied in theearly stages o decline. However as the diseasemay be present without showing symptoms,sometimes control is not successul. Phytophthoramay be in existing soil as a dormant spore orit can be introduced into the home garden via

Bardi grubs on Xanthorrhoea

contaminated soil. There have been examples oPhytophthora moving through the soil water roma higher elevated garden, to another garden at alower level some distance away aecting a varietyo susceptible plants such as roses and coniers.

The Department o Agriculture and Food (AgwestPlant Laboratories 9368 3721 ) can test soil

samples or a ee.

Foliage disease

There are ew oliar pathogens recorded or Xanthorrhoeas. The plants have adapted todry conditions by having thick waxy needles toprevent water loss, as well as acting as a barrier toungal attack. Foliar lea spot pathogens are morecommon on the coastal plains than urther inland.

 Anthracnose ( Colletotrichum xanthorrhoeae )

Symptoms are frst visible as black ecks in thelea tissue. These ecks develop to encompassthe entire lea and will spread to the rest o thecrown. Apply mancozeb to protect leaves romurther inection. However, i the disease hasprogressed too ar, control may be ineective.

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ISSN 0726-934X

Copyright © Western Australian Agriculture Authority, 2010

Copies o this document are available in alternative ormats upon request.

3 Baron-Hay Court South Perth WA 6151

Tel: (08) 9368 3333 Email: [email protected] Website: www.agric.wa.gov.au

Other factors contributing to decline

•Run-o rom lawn phosphates into garden beds

•Transplant shock can in some cases takemonths to appear and is more prevalent duringthe summer months

•Insufcient drainage in clay soils causingwaterlogging

•Mulching too close to trunk

•Drought stress

•Saline bore water

 A good indication to determine i the tree is tosurvive, is to pull gently at the centre needles. Ithey come away, this indicates the crown is rottingand unortunately there is no remedy. In somecases burning the ‘skirt’ will promote growth asmentioned previously.

References:

Shivas, RG, Bathgate, J and Podger , FD1998, Colletotrichum xanthorrhoeae sp.nov.on xanthorrhoea in Western Australia , MycologicalResearch, volume 102 (3): 280-282

20102576-4/10-ID10437

Specimen identication requirements

When sending or delivering samples, theollowing inormation is required:

•Collector’s name, location (where thespecimen was ound), ull address, telephonenumber and e-mail address, description o thedamage and date collected.

Department o Agriculture and FoodPest and Disease Inormation Service3 Baron-Hay Court, South Perth WA 6151Freecall: 1800 084 881E-mail: [email protected]

Colletotrichum xanthorrhoeae on Xanthorrhoea preissii