Root lesion nematodes (RLN), especially Pratylenchus thornei (Pt), can cause wheat yield losses of up to 50 percent in intolerant bread wheat varieties.
A second RLN species, P. neglectus (Pn), can also cause significant yield loss but generally not at as high a level as Pt. Fortunately research, backed by practical application, more or less, can now reduce the impact of these once feared pests to negligible yield losses.
Dr Steven Simpfendorfer, NSW DPI Tamworth Agricultural Institute based, and leader of research and extension programs focusing on management of winter cereal diseases in northern NSW, stresses that integrated control strategies have largely eliminated once common high yield losses from RLN in NSW.
Especially important have been the development and release of more varieties with good tolerance to Pt, and rotations that include crops and varieties with good resistance to this RLN species. RLN populations have declined in north-west NSW over recent seasons also as a consequence of prolonged drought from 2017-2019.
Dr Simpfendorfer reports that previous research identified varieties, like Strzelecki, that while high yielding, were highly susceptible to Pt. These have largely been replaced with recently released varieties that combine yield high (in some cases higher) but also have good tolerance to Pt. Modern tolerant wheat varieties even with moderate soil Pt levels significantly limit yield loss from the RLN.
Wheat varieties with good Pt tolerance include Lancer, Coota, Flanker, Reliant, Coolah, Suntop, Sunmaster, Sunchaser and Sunflex. Barley varieties with good Pt tolerance include Compass, Commander, Leabrook, La Trobe, Rosalind, Hindmarsh, Fathom, and Beast.
Research conducted by various organisations with GRDC co-examining Pt resistance of various crops and varieties demonstrated that both play an important role in keeping soil numbers low. Crops with good Pt resistance include canola, sorghum, oats, cotton, sunflower and linseed. Field peas, chickpeas and mung beans are rated medium risk for build-up of Pt with variety differences in resistance levels.
Chickpea varieties have variable tolerance to Pt with some having good tolerance. These include PBA HatTrick, PBA Seamer, CBA Captain, Kyabra and PBA Boundary. Note variety and crop tolerance or resistance, or lack of tolerance or susceptibility for Pn is generally different to Pt. More details of these difference is available in publications such as the NSW DPI Winter Crop Variety Sowing Guide (2021) and the GRDC publication Root Lesion Nematode Fact Sheet (northern).
Soil testing is an important part of RLN management Dr Simpfendorfer stresses. PreDicta B is a DNA-based soil analysis undertaken via SARDI. Other crop issues like Fusarium crown rot (FCR) are also assessed using this science based credible test. Generally soil testing is provided by accredited agronomists.
Wheat symptoms of RLN can be confused with nutrient deficiencies and/or moisture stress, therefore also the need for soil testing. Brown root lesions, roots with reduced branching and hairs, reduced ability to penetrate into the soil all add to an inefficient root system. Lower leaf yellowing, reduced tillering and biomass, are commonly noted later in the season when sub soil moisture is more critical. In early stages of infection localised patches of poor growth is typical in intolerant varieties.
Under fertilising generally worsen Pt yield impacts and over fertilising is unlikely to compensate for poor variety choice stresses Steve Simpfendorfer. Strategies for FCR control are also import. When combined infection from RLN and FCR occurs a crop's ability to access soil water and limit expression of FCR is more compromised. This is an especially serious as spring warms and soil water is more critical. Clean fallows are also important as various weeds can also host these soil pests he adds.
Pt has reduced in importance in the northern region through adoption by growers of integrated management strategies. However, vigilance is still required to ensure susceptible varieties are not adopted or effective management strategies forgotten.
Next week: New faba bean variety a lift in yield. Plus high grain quality.
- Bob Freebairn is an agricultural consultant based at Coonabarabran. Email robert.freebairn@bigpond.com or contact (0428) 752 149.
