Preliminary findings from Department of Primary Industries and Regional Development (DPIRD) – formerly DAFWA – trials in Gibson, near Esperance in 2014 and Wongan Hills, in the central grainbelt, in 2015, showed medium to high levels of RLN at the start of those seasons led to cereal yield losses of up to 19 per cent from P. quasitereoides and P. neglectus.

At the Wongan Hills trial site, set up with Grains Research and Development Corporation (GRDC) investment, high P. neglectus levels led to yield losses ranging from 11-18% across the wheat varieties tested. Barley yields were reduced by up to 10% under high nematode pressure early in the season. 

At the Wongan Hills trial site, set up with GRDC investment, high P. neglectus levels led to yield losses ranging from 11-18% across the wheat varieties tested. 

Barley yields were reduced by up to 10% under high nematode pressure early in the season.

DPIRD Agriculture and Food senior nematologist Dr Sarah Collins said it was valuable to assess all crops for potential RLN damage this winter and test suspect paddocks to help manage this pest through future rotation planning.

“This is because effective management relies on sowing resistant crops that will reduce nematode densities and/or more tolerant varieties of susceptible crops that will typically have less yield loss in the presence of RLN pressure,” she said. 

RLN SPECIES AFFECTING WA CROPS

RLNs are the main type of plant parasitic nematodes affecting WA crops and the incidence of these pests is increasing right across the grainbelt.

The common RLN species found in WA are P. neglectus, P. quasitereoides, P. thornei (not as widespread) and P. penetrans (more rare but highly impacting).

These plant parasitic nematodes are microscopic and concentrated in the feeder root zone, which is typically in the top 0-10 centimetres of the soil in the western region.

RLN can dehydrate over summer and re-start their lifecycle when the soil becomes moist after soaking rainfall events. Only one nematode is needed to start a population, making on farm biosecurity and crop rotation crucial management tools.

Of 340 paddocks assessed pre-season in 2016 by DPIRD from nematode sampling data (derived from testing services, grower groups, advisers and growers), RLN were present in 84% of the samples. In 56% of these samples, levels were high enough to potentially cause a significant yield loss in a cereal (according to the PREDICTA® B risk categories). 

In the majority of these samples, P. neglectus was the most common nematode species detected (51%) followed by samples containing a mixture of RLN species (24% and typically P. neglectus and P. quasitereoides together), P. quasitereoides alone (7%) and P. thornei alone (0.3%). In 18% of the samples no RLN were detected.

From 280 PREDICTA® B tests carried out pre-sowing in WA for 2017, 41% of samples showed a medium to high risk of yield loss if a wheat or barley crop was sown in the paddock due to P. neglectus – which is the most common RLN found in WA.

For the nematode P. quasitereoides, which is found in fewer paddocks, 13% of samples showed there was a medium-high risk of yield loss in 2017 and for P. thornei it was 4%. 

Dr Collins said surveys in previous years had shown RLN to be at yield-limiting levels in about 40% of WA paddocks sampled and potentially causing crop losses of 15-50%. 

She said the notable increase in RLN impacts in the western region in recent years could be due to one or a combination of factors, including increasing awareness of identifying RLN issues, increased usage of susceptible crops in rotations and a series of warm seasons conducive to RLN multiplication. Researchers are hoping that dry seasonal conditions unfolding across the western region in 2017 will reduce the extent of RLN impact on WA crops next year.

WHAT TO LOOK FOR IN THE CROP

Typically, in susceptible areas and long-term average ‘typical’ WA seasonal conditions, cereal crops affected by RLN will appear ‘wavy’ and uneven in growth and may have:

• patches of poor growth
• more weeds
• yellowing plants
• plants with poor tillering
• stunted plants and/or root systems
• roots that lack lateral branches
• roots with brown lesions from nematode pruning
• plants that are wilting or dying (under water stress)

Dr Collins said while above-ground symptoms in cereal crops are diagnostic, they could be confusing as many biotic and abiotic stresses (including nutrient and water deficiency, soil constraint limitations and rhizoctonia) have similar expression.

She said more information about RLN diagnosis could be found on the agriculture hub of DPIRD’s MyCrop website at: www.agric.wa.gov.au/wheat-diagnostic-tool.

It’s important to identify RLNs to a species level as different crops and varieties can react differently to the RLN species present. For example, lupins are resistant to P. quasitereoides and P. neglectus but are highly susceptible to P. penetrans. 

Sending soil or plant root samples from suspect areas to a testing service is the only way to correctly identify the RLN species (or other root/hypocotyl diseases) present in the paddock and the incidence level. 

TESTING SERVICES

Soil and plant root testing and monitoring for RLN is carried out by: DPIRD Diagnostic Laboratory Services (DDLS)-Plant Pathology (formerly AGWEST Plant Laboratories).

Soil and plant root samples are sent direct to DDLS. For more information, go to: www.agric.wa.gov.au/bacteria/ddls-plant-pathology-services. 

Dr Collins explains how to best take soil samples for nematode testing on the YouTube video ‘Root Lesion Nematodes’ that can be found HERE.

For more information about PREDICTA® B click HERE.

RLN DAMAGE 

Previous long-term research in WA has shown RLN infestations cause average cereal yield losses of 0.27 tonnes per hectare (or 270kg/ha) for every 10 RLN detected in one gram of soil. Commonly grown wheat and barley varieties in WA are intolerant to P. neglectus and P. quasitereoides. 

Recent case studies conducted by DPIRD researchers in WA found the average yield loss under high pressure from these RLN was 7-15% for wheat and 5-7% for barley, respectively for each species of nematode.

MONITORING AND RESEARCH – 2017 AND BEYOND

This year, DPIRD researchers are continuing to investigate the impacts of P. neglectus, P. quasitereoides and P. penetrans in a range of crops across WA environments and soil types. 

Also, to increase the potential opportunities for break crops available to growers, they are testing the resistance of a range of pasture varieties to P. neglectus and P. quasitereoides. 

Trials are being conducted to test the effect of different rates, forms and timing of nitrogen on P. quasitereoides survival and multiplication in wheat. Liming trials are also being monitored to determine the effect of increasing soil pH on RLN multiplication during a growing season.

Dr Collins says researchers are assessing options for resistant crops and varieties that reduce nematode densities and tolerant crops and varieties that have reduced yield loss in the presence of RLN. She says a better understanding of the effects of rotational crops on RLN densities will improve management of subsequent cereal crops. 

“Understanding the RLN tolerance of current wheat, barley, pulse and oilseed varieties also helps to estimate the potential economic effects of RLN in WA – and development of appropriate choices for infested paddocks in future,” she says.

GRDC Project Codes: DAV00128

Contact:

Sarah Collins, DPIRD

08 9368 3612

sjcollins@agric.wa.gov.au