Managing root lesion nematodes pre-sowing

Author: Melissa Williams | Date: 22 Mar 2016

Root lesion nematode (RLN) numbers were unprecedented in parts of the Western Australian grainbelt last season, causing significant cereal yield losses in some paddocks.

In the lead-up to sowing this year, it is recommended growers undertake soil testing from paddocks suspected of having nematode damage in 2015 and then carefully plan crop types and varieties.

It is important to correctly identify the species of nematodes present due to differences in the susceptibility of break crops and varieties to different RLN.

The GRDC’s western region Wheat GrowNotes online resource contains useful information about testing for and managing nematodes and can be found here.

The GRDC also has a handy ‘Tips and Tactics’ publication for managing RLN, which can be found here.

Incidence of RLN in WA

At a Wongan Hills trial site in 2015, the Department of Agriculture and Food WA (DAFWA) recorded RLN numbers previously thought impossible in this State.

And in a targeted survey of 31 paddocks by DAFWA right across the grain belt, 23 also had potentially yield-limiting populations of nematodes at a medium to high risk.

What remains uncertain is whether RLN damage spiked last year in WA on the back of crops being moisture stressed at the end of the season, or whether numbers will keep rising in 2016.

In the Great Southern and South Coast regions, Farmanco agronomy consultant Frank Boetel says he has been seeing a rapidly increasing prevalence of RLN in recent years.

Latest South Australian Research and Development Institute (SARDI) PreDicta B® maps - compiled from more than 360 PreDicta B® soil samples from across WA in 2015 - indicate many paddocks in the State’s main crop growing areas now have RLN at potentially yield limiting levels.

Of the 360-plus PreDicta B® WA samples last year, 65 per cent had Pratylenchus neglectus present and 30 per cent had P. quasitereoides (formerly P. teres) present.

The SARDI distribution maps for soil borne pathogens that include information gathered from grower PreDicta B® soil samples during autumn 2015 can be found here.

Surveying of RLN through DAFWA’s Focus Paddock project has shown numbers of these microscopic endoparasites have been increasing right across the WA grainbelt for the past five years at least.

Portrait of Sarah Collins

DAFWA nematologist Dr Sarah Collins is working on GRDC-funded research into the tolerance and resistance of wheat, barley, lupin and canola varieties to commonly found root lesion nematodes (RLN) in WA.

Photo: DAFWA

DAFWA nematologist Dr Sarah Collins says 54 per cent of the 180-plus Focus Paddocks assessed to the end of 2015 had RLN populations at levels that may cause 5 to 50 per cent yield loss (recording greater than two RLN per gram of soil.

She says this is a six per cent increase from 2013, when nematode species were found in 90 per cent of the 130 Focus Paddock project paddocks sampled and 48 per cent of affected paddocks had levels high enough to cause 5 to 50 per cent yield loss.

In 2014, testing by DAFWA’s AGWEST Plant Laboratories (APL) found the average number of RLN in infested plant samples it received had increased to about 31,000 RLN per gram root from about 7000 RLN/g root in 2011.

Paddocks with the highest numbers were from barley crops infested with P. quasitereoides, one with 55,000 RLN/g root in 2012 and the other with 220,000 RLN/g root in 2014.

Farmanco PreDicta B® surveys from 60 of its clients in Great Southern and South Coastal districts tell a similar story.

From 167 samples in 2014, 90 per cent had P. neglectus present - of which 40 per cent were at medium levels and eight per cent at high levels.

From 145 samples In 2015, 90 per cent had P. neglectus present - of which 53 per cent were at medium levels and 19 per cent at high levels.

Importance of pre-sowing testing

Growers are encouraged to undertake soil testing from paddocks suspected of having nematode damage in 2015.

It is important to correctly identify the species of nematodes present due to differences in the susceptibility of break crops and varieties to different RLN.

The common RLNs found in WA are P. neglectus, P. quasitereoides and P. penetrans. Soil testing for confirmation of nematodes and species identification can be carried out by:

Taking a root or soil sample for nematode diagnosis

Soil sampling guidelines for RLN include:

  1. Using a soil corer or trowel to collect a soil sample to a depth of 0-10cm.
  2. Taking samples in the crop rows, close to root systems.
  3. Sampling from 12 to 20 locations towards the margins of poor crop growth areas, taking a 500g sample at each.
  4. Sealing the soil in a plastic bag.

(SOURCE: GRDC western region Wheat GrowNotes)

Plant sampling guidelines for RLN include:

  1. Collecting plants from several locations at the margins of the impacted area, making sure to keep the root system intact.
  2. Sending a separate sample collected from a healthy area of the paddock for comparison.
  3. Including notes about paddock symptoms when sending in a sample for testing.
(SOURCE: Dr Sarah Collins, DAFWA)

DAFWA has produced a useful video outlining how to take a plant sample that can be viewed here.

Managing RLN in 2016

There are limited in-crop options for preventing damage from nematodes.

After species identification, management hinges on crop and variety choice for the coming season and beyond. The goal is to break the pest cycle.

Dr Collins says a run of conducive seasons favourable to RLN and increasing use of canola in crop rotations is likely to be contributing to rising nematode numbers across much of WA.

She says the host range for nematodes is broad and includes cereals, oilseeds, grain legumes, pastures and many broadleaf and grass weeds.

Well-managed rotations can minimise the damage caused to cereal production.

As outlined in the GRDC’s Wheat GrowNotes for the western region, RLN management includes:

  1. Planning crop rotations with resistant or non-host break crops and resistant pastures to inhibit nematode reproduction/build-up (resistance) and boost yields under RLN pressure (tolerance).
  2. Using crop varieties that are resistant or tolerant to the RLN species in the paddock. Resistance ratings for P. neglectus and P. quasitereoides for wheat and barley can be found in the current WA Wheat and Barley Variety Guides here
  3. If RLN levels are high to very high, consider growing a moderately resistant (MR) or resistant (R) crop or pasture for one or more seasons.
  4. Avoiding sowing consecutive host crops across season.
  5. Maintaining healthy soils and good crop nutrition, especially at crop establishment.
  6. In the lead-up to and around harvest, monitoring cereal crops for potential damage.

Experiences in the field - Great Southern/South Coast

Damage caused by root lesion nematodes in-crop.

Photo: DAFWA

In recent years, Frank Boetel has seen RLN numbers escalate rapidly on many of his client’s properties - both as a result of continuous cereal rotations and in cereals following canola crops.

His PreDicta B® surveys through Farmanco are uncovering a build-up in numbers of both P. neglectus and P. quasitereoides, which historically has not been as common in this region.

He says the nematodes are causing significant yield losses in wheat and canola crops, measured across years using the same GPS coordinates.

Frank says increased plantings of canola appear to be exacerbating the problem and many growers are now being forced to consider planting more area to lupins and taking a profit-hit.

His advice to growers is to: continue monitoring RLN numbers through annual soil tests; control the green bridge over summer; consider lupins as a break crop; carefully choose barley and wheat varieties; and sow wheat crops earlier if there is an opportunity to achieve higher vigour.

DAFWA tolerance and resistance trials for RLN

In 2015, DAFWA found wheat, barley and canola crops were susceptible to P. neglectus, P. quasitereoides and P. penetrans. Lupins were resistant in all P. neglectus and P. quasitereoides trials, but proved highly susceptible to P. penetrans.

DAFWA is in the process of analysing 2015 trial data to determine RLN impacts on crop yield.

Dr Collins says preliminary results show there was yield loss for wheat, barley and canola crops, but the degree of loss differed with location.

This was the first time canola yield impacts have been tested in WA.

DAFWA is conducting further RLN tolerance trials to develop a better understanding of yield impacts for these crops across the different agricultural regions in WA.

Economic impact of RLN

It is estimated cereal root diseases as a whole cost Australian grain growers more than $200 million annually in lost production.

GRDC is funding a nationally-coordinated nematode research program to quantify the yield and economic impacts of RLN in crop production systems.

Part of this project is to refine management options for these costly soil pathogens and improve relationships between PreDicta B® pre-sowing pathogen levels and likely on-farm yield loss.

More information

Dr Sarah Collins, DAFWA nematologist
08 9368 3612

Brenda Coutts, AGWEST Plant Laboratories
08 9368 3721

Shawn Rowe, senior research officer, SARDI for PreDicta B®
0477 744 305


Melissa Williams, Cox Inall Communications
0428 884 414

Useful resources

GRDC western region Wheat GrowNotes and Canola GrowNotes at this link.

GRDC ‘Tips n Tactics’ Root Lesion Nematodes at this link.

DAFWA AGWEST Plant Laboratories at this link.

PreDicta B® at this link.

DAFWA Bulletins: Root Lesion & Burrowing Nematodes in Western Australian cropping
systems (no. 4698) and Root disease under intensive cereal production systems (no. 4732)
by following this link.

GRDC - The current and potential costs from diseases of wheat in Australia at this link.

GRDC Project Code DAN00175, DAS00122, DAS00123, DAS00125, UWA00152, DAW0021, DAW00174, DAW00212, DAS00137, DAW00157, DAW00201, DAW00209

Region West