Australia
October 25, 2013
Agronomists and grain growers are being urged to use in-season testing services for root lesion nematodes (RLN) if their presence is suspected.
Tests will confirm species and population levels of these microscopic endoparasites and help the Department of Agriculture and Food WA (DAFWA) characterise distribution and gather resistance information for crops and varieties grown in WA.
This research, jointly funded by GRDC and DAFWA, is vital because yield loss can occur without careful planning in crop variety selection and no chemicals are currently available to economically control RLN in broadacre cropping systems.
Management is based on reducing nematode numbers in the year(s) prior to a crop by:
- Crop rotations with resistant or non-host break crops and pastures.
- Using resistant varieties of a crop to inhibit nematode reproduction.
- Control of summer weeds and plant nutrition.
- In the cropping year, using tolerant varieties – particularly of wheat – that suffer little or no yield loss even when RLN are present in the soil (but be aware these can still increase RLN numbers during the season).
TYPES OF NEMATODES
Pratylenchus neglectus is the RLN species most commonly found damaging crops in WA.
P. teres, P. thornei and P. penetrans are the other main RLN species that can impact on crops in this State.
P. teres is unique to WA and appears to have potential to impact on cereal yields more severely than other RLN species.
Growers need to know which species is present, as crop species and cultivars resistant to one nematode species may be susceptible to another – meaning suitable rotations will vary.
DAFWA’s nematology team is conducting research to quantify the losses from RLN and determine crop and variety resistance information for the various species that impact growers across the WA grainbelt.
WHAT’S THE DAMAGE?
RLN surveys carried out by DAFWA have found RLN populations in 5.3 million hectares – or about 60 per cent – of WA’s cropping area.
These nematode populations are yield-limiting in at least 40 per cent of all crop paddocks.
This year, DAFWA researcher Sarah Collins has seen widespread damage from RLN in every southern WA cropping zone - especially in crops growing after a 2012 canola phase.
In many cases, growers had a significant green bridge after solid March rains. Plant stress from the prolonged dry spell in early winter may also have left crops more susceptible to RLN infestation.
Sarah has found some cereal paddocks with an estimated 50 per cent crop loss due to nematodes, significantly affecting returns.
WHAT TO LOOK FOR
RLN damage root systems, reducing the plant’s ability to efficiently take up water and nutrients and increasing susceptibility to other diseases.
RLN symptoms are commonly mistaken for nutrient deficiencies, soil limiting factors or rhizoctonia.
This year, big patches or uneven waves of crop growth in paddocks are being seen in cereals affected by RLN. Up close, plants are often smaller, have reduced tillering, wilt easily and may be dying-off.
To check for nematodes, dig up a sample of the plants you suspect of being affected by RLN and some healthy plants for comparison. Shake off the soil for close inspection.
If nematodes are present, roots will be stunted, lack lateral roots and may have brown lesions from nematode pruning.
TESTING FOR RLN
If you suspect you have RLN issues, contact Sarah Collins at DAFWA on 08 9368 3612 or email: sjcollins@agric.wa.gov.au
Plant samples can be sent to Sarah to confirm species and provide data for her RLN survey project.
Samples from problem areas can also be sent to the AGWEST Plant Laboratories.
It is important to send whole plants, including intact root systems and soil – for both suspect and healthy samples.
Sarah says knowing which nematode species is present allows better pest management in subsequent seasons with well planned rotations.
She says the DNA-based soil testing service PreDictaB, provided by the South Australian Research and Development Institute, is currently in development for P.teres and P. penetrans - but can be a valuable pre-seeding tool to improve detection of other soilborne root diseases.
ROTATION, TOLERANCE AND RESISTANCE RESEARCH
Wheat, canola and chickpeas are susceptible hosts for P. neglectus.
But Wyalkatchem, Bumper, Fortune, Magenta and Yipti wheat varieties and several canola varieties do have some resistance to this species of RLN.
Barley, oats, durum wheat and vetch also have moderate resistance to P. neglectus, while field peas, narrow-leafed lupins, faba beans and triticale are highly resistant.
For P. teres, it appears wheat and barley are highly susceptible and canola less so. Lupins are the most resistant.
Tolerance to P. teres in 2012 DAFWA trials at Toodyay showed Yipti and Wyalkatchem did not suffer any yield loss under nematode pressure, compared to a 24 per cent yield loss in Carnamah and Emu Rock, 16 per cent yield loss in Machete and 12 per cent yield loss in Arrino and Westonia.
Sarah says this was the first tolerance field research for P. teres and rotational advice will improve on the back of continued surveying and characterising of cultivar resistance and tolerance this year.
Although more trials are necessary to be confident of results for P. teres, trials to date have demonstrated that tolerance and resistance for P. teres can be independent and variety selection is an important tool to reduce RLN levels in soil over time.
The keys to successful RLN control are avoiding consecutive crops of susceptible plants and introducing more resistant varieties to the rotation.
Crop variety guides for 2014 will include information about RLN resistance ratings.
Useful resources:
GRDC Plant Parasitic Nematodes Fact Sheet: www.grdc.com.au/GRDC-FS-Plant-Parasitic-Nematodes-SW
DAFWA Bulletin 4698 and 4732: Root Lesion & Burrowing Nematodes in Western Australian Cropping Systems and Root Disease Under Intensive Cereal Production Systems: www.agric.wa.gov.au
Species
