Australia
July 28, 2014
WA growers are encouraged to find out what species and levels of root lesion nematodes (RLN) are present in their soils during the growing season.
The three main RLN found in WA are Pratylenchus neglectus, P. teres and P. thornei.
These microscopic endoparasites affect about 5.3 million hectares - or 60-65 per cent of the State’s cropped area – and are an increasing problem.
Latest Department of Agriculture and Food, Western Australia (DAFWA) surveys show RLN populations are at yield-limiting levels in at least 40 per cent of cropping paddocks and cause crop losses typically ranging from 15-50 per cent.
The GRDC and its Regional Cropping Solutions Networks (RCSNs) in all five western port zones have identified RLN as a high priority for research.
Why test for nematodes
Pre-seeding or in-crop soil testing can help plan rotations that help to manage potential damage from RLN in infested paddocks.
Correct RLN diagnosis will also assist DAFWA characterise nematode distribution and gather further resistance information for crop types and varieties grown in the western region.
Such research is vital because there are currently no chemicals available to economically control nematodes in broadacre cropping systems.
Best practice management for these pests centres on:
- Planning crop rotations with resistant or non-host break crops and pastures to inhibit nematode reproduction/build-up (resistance) and boost yields under RLN pressure (tolerance)
- Using crop varieties that are resistant or tolerant to the RLN species in the paddock
- Controlling summer weeds and the green bridge and adopting good plant nutrition
- Building the natural suppressiveness of soil to RLN.
Pre-seeding testing for RLN
PreDicta B can test for P. neglectus and P. thornei.
A test for P. teres is also under development.
The PreDicta B testing service is available from the South Australian Research and Development Institute (SARDI) until mid-May through accredited agronomists.
Note, there were some changes to soil sampling protocols for PreDicta B in 2014 and further information about the test is available from Shawn Rowe, of SARDI, phone: 0477 744 305, email: shawn.rowe@sa.gov.au
In-crop testing for RLN
If RLN is suspected, contact DAFWA researcher Sarah Collins or send crop samples to her for confirmation of species and to provide data for her nematode survey project.
For a broader diagnosis of problem areas, samples can also be sent to the AGWEST Plant Laboratories. Information about this service is available under Our Services on the DAFWA website: www.agric.wa.gov.au
It is important to send whole plants, including intact root systems and soil – for both suspect and healthy samples.
RLN symptoms are commonly mistaken for nutrient deficiencies, soil limiting factors or rhizoctonia.
Look for big patches or uneven waves of crop growth in paddocks. Up close, plants are often smaller, look chlorotic (yellowing), have reduced tillering, wilt easily and may be dying-off.
If nematodes are present, roots may be stunted, lack lateral roots and may have brown lesions from nematode pruning.
What to do with test results – variety and rotation planning
If there are high to very high RLN levels in a paddock (>10 nematodes/mL of soil or >10 000 nematodes/gram dry root - severity score three and four), DAFWA recommends growing a moderately resistant (MR) or resistant (R) crop for one to two cropping seasons.
Taking action with rotations can help to reduce nematode numbers to a level that is not yield-limiting.
Resistance ratings for P. neglectus and P. thornei for wheat and barley can be found in the 2014 Crop Variety Sowing Guides for WA.
DAFWA has robust resistance information for P. neglectus from glasshouse and field trials.
The recommendation for a paddock infested with high levels of P. neglectus is to grow lupins (Tanjil
), field peas (Kaspa), serradella (Charano yellow, Yelbini yellow or Margurita French) or sulla (Flamenco).
It is recommended not to grow wheat, barley, canola, chickpea, mustard, Trifolium spp., Medicago spp. or Biserulla spp. on these paddocks.
But Wyalkatchem, Bumper, Fortune, Magenta and Yipti wheat varieties and several canola, oats and vetch varieties do have some resistance to P. neglectus.
DAFWA is continuing to collate information about the resistance of crops and varieties to P. teres, which is unique to WA.
For P. neglectus and P. teres, to date research indicates that field peas and lupins are generally resistant and wheat, barley and canola are generally susceptible. DAFWA has conducted a number of cereal variety tolerance trials.
This work continues in 2014, including: P. teres sites in Esperance, Williams and Yornup; and P. neglectus sites in South Stirling, Wongan Hills, Cunderdin and Nyabing.
In 2013, P. penetrans caused visible symptoms in paddocks of canola and pasture. DAFWA research has indicated crops that are resistant to P. penetrans are often highly susceptible to P. neglectus or P. teres, highlighting the importance of knowing which species of RLN is present - as management of one RLN species may be causing an increase in another.
Using resistant crops reduces nematode numbers and may allow a tolerant wheat crop to be planted in the future.
Building a natural defence against RLN
Through its Soil Biology Initiative II (SBI II) project, GRDC has been investing in national research to develop soils that can be suppressive to nematodes and other diseases.
This is part of a wider strategy to improve soil health, increase sustainability and enhance biocontrol mechanisms against soilborne pathogens.
A wide range of parasites and predators of nematodes are found in healthy soils and can provide a degree of protection against plant-parasitic nematodes.
Dr Graham Stirling, of Biological Crop Protection, is part of the SBI II team investigating interactions between these beneficial soil-microorganisms and nematode management.
He says preliminary results from soil sampling of well-managed, no-tillage and residue retained cropping systems in WA and SA indicate that natural suppressiveness to plant-parasitic nematodes in crop soils may exist and can be improved.
For example, a Liebe Group site that has been cropped with P. neglectus hosts for eight of the past 10 years has been found to have low levels of this nematode – indicating that a physical, chemical or biological constraint is likely to be limiting nematode population growth.
However, further research is required to determine levels of natural suppressiveness to Pratylenchus species in WA soils, identify the main natural enemies of these nematodes, and determine the soil carbon levels required to enhance suppressiveness.
Useful resources:
AGWEST Plant Laboratory, 08 9368 3721, www.agric.wa.gov.au - click on services and then AGWEST
PreDicta B tests: Shawn Rowe, SARDI 0477 744 305, shawn.rowe@sa.gov.au, Mobile: 0401 122 115. Postal Address for PreDicta B samples: C/- SARDI RDTS, Locked Bag 100, Glen Osmond SA, 5064
GRDC Plant Parasitic Nematodes Fact Sheet: www.grdc.com.au/GRDC-FS-Plant-Parasitic-Nematodes-SW
DAFWA Bulletins: Root Lesion & Burrowing Nematodes in Western Australian cropping systems (no. 4698) and Root disease under intensive cereal production systems (no. 4732) which can be found by searching ‘root lesion nematodes bulletin' on the DAFWA website www.agric.wa.gov.au
Dr Graham Stirling’s new book: ‘Biological control of plant-parasitic nematodes’ (second edition) Soil Ecosystem Management in Sustainable Agriculture: Inquiries to the publisher: www. cabi.org/bookshop/
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