Stop disease and pest cycles in their tracks with crop checks this harvest
Author: Melissa Williams | Date: 31 Oct 2014
- Consecutive cereal crops are at the highest risk of yield losses from soilborne diseases and pests.
- Test suspect wheat and barley paddocks for crown rot, rhizoctonia and root lesion nematodes this harvest to prepare for rotation planning in 2015.
- Stubble and weed management during summer can reduce the spread and impact of cereal crown and root diseases and soilborne pests.
- Registered fungicides are now a vital part of integrated rhizoctonia management and there are promising new in-furrow fungicides becoming available.
Growers are being urged to test wheat and barley crops before or at harvest that are showing signs of soilborne diseases and pests - especially fusarium crown rot, rhizoctonia bare patch and root lesion nematodes (RLN).
A blanket management strategy can’t be used for all soilborne diseases and pests, so it is vital to know what is present in the paddock.
The GRDC and Department of Agriculture and Food, Western Australia (DAFWA)-developed MyCrop ‘app’ can assist with disease diagnosis.
Plant and stubble samples can be sent to DAFWA’s diagnostic service, AGWEST Plant Laboratories (APL), for correct identification of any crown or root diseases or RLN pests. Results are typically back within two-four weeks.
After harvest and into autumn, the South Australian Research and Development Institute (SARDI) PreDicta-B® soil test – which is available through accredited agronomists - can also diagnose the presence of these diseases and pests in suspect paddocks.
Testing this year will help with rotation planning for 2015, as crop choice following cereals is a major management tool to break disease and pest cycles.
DAFWA research officer Daniel Hüberli says the lead up to and during harvest is an ideal time to monitor cereal crops, identify any diseases or RLN pests and start planning to minimise their impact next year.
Crown rot is caused by the soilborne fungus fusarium (F. pseudograminearum and F. culmorum), which infects plants at the crown and reduces water supply to the head.
DAFWA reports an increase in detections of crown rot this year, especially in the eastern wheatbelt, on the back of more intensive cereal production and favourable seasonal conditions in 2013 and 2014. In some cases, 30-50 per cent of wheat paddocks have been affected.
Signs of crown rot:
- White head formation that fail to ‘grain fill’, usually scattered across the paddock
- Distinctive honey brown discolouration of the base of the stem or lower node, evident when leaf sheaths are removed
- Pink colouration at the base of the plant may sometimes be present.
Management of crown rot
There are currently no registered fungicides to control crown rot and rotation with non-cereals is the key management tool for affected paddocks. This means 2014 observations will be critical for break-crop planning for 2015.
Daniel says if plant or soil testing detects paddocks with a high risk of crown rot for next year, the best options are:
- Minimising stubble cultivation, spreading, slashing or grazing this summer (this can spread infected residues over paddocks)
- Ensuring good grass weed control over summer and in break crops
- Sowing a non-cereal break crop, such as canola or pulses
- Using less susceptible cereal varieties, such as Emu Rock, and sowing early so crops are less vulnerable to a hard finish (which causes the expression of white heads). Ratings of susceptibility will be added to future GRDC-DAFWA Wheat and Barley Variety Guides when data from trials that started this year are completed
- Using inter-row sowing into standing cereal stubble.
GRDC is funding a range of DAFWA trials to assess cereal variety tolerance to crown rot and improved management strategies through its new national project ‘National crown rot epidemiology and management’.
In 2014, a three-year WA trial program was started to assess yield loss in wheat and barley due to crown rot and other research is looking at rotation benefits and inter-row sowing to improve cereal crop yields.
The GRDC’s national crown rot project will also continue to investigate genetic solutions to this fungal disease by breeding more resistant cereal varieties and to undertake molecular research to unravel how the crown rot pathogen causes disease.
Rhizoctonia bare patch
Caused by the fungal root pathogen Rhizoctonia solani AG8, rhizoctonia bare patch is an increasing problem right across the southern Australian grainbelt.
Incidence has been high across parts of WA this year after prolonged dry summer and autumn conditions and where consecutive cereal crops were sown.
Signs of rhizoctonia
Symptoms of rhizoctonia root rot vary according to when infection occurs. Check for distinct patches of poor growth (more likely in late-sown crops) and general unevenness of paddocks (more likely in early sown crops) and if suspect, undertake plant and/or soil testing.
Management of rhizoctonia
Effective control of rhizoctonia requires reducing inoculum levels in affected paddocks and controlling the infection process. Strategies include:
- Planting cereals after grass-free canola crops
- Sowing early and with soil disturbance below the seed (to about 10cm) to encourage early root growth
- Using a registered fungicide (seed dressing or in-furrow) in paddocks with low to moderate disease levels
- Maintaining adequate crop nutrition based on soil test results.
In-furrow fungicides and seed dressings for rhizoctonia
Fungicide seed dressings are an integral tool to rhizoctonia management and long term GRDC-funded trials have shown these can lift wheat and barley yields by about 5 per cent compared to no treatment.
Dividend® - with the actives difenoconazole and metalaxyl-m - and Rancona® Dimension - with the actives ipconazole and metalaxyl-m - are registered seed treatments to suppress rhizoctonia root rot.
In 2013, VibranceTM - with the active ingredients sedaxane, difenoconazole and metalaxyl-m - and EverGol® Prime - with the active ingredient penflufen – became available.
Extensive GRDC-funded trials in WA and SA from 2011-13 and large scale trials by Syngenta and Bayer CropScience this year assessed in-furrow fungicides for rhizoctonia.
Registration of some of these products is likely to be granted for the 2015 season.
Root Lesion Nematodes (RLN)
The three main RLNs found in WA are Pratylenchus neglectus, P. teres and P. thornei. P. penetrans is uncommon in WA broadacre cropping, but can be devastating to crops when present.
These microscopic endoparasites affect about 65 per cent of the State’s broadacre cropping area and are an increasing problem, with high levels found this year.
Latest DAFWA surveys show RLN populations are at yield-limiting levels in at least 40 per cent of affected cropping paddocks and can cause crop losses of up to 50 per cent.
For rotation planning, WA growers are encouraged to find out what species and levels of RLN are present in their soils by testing in-crop or pre-seeding. This is important as crops can vary in susceptibility depending on the RLN species.
Signs of RLN
RLN symptoms are commonly mistaken for nutrient deficiencies, soil limiting factors or rhizoctonia.
Look for 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. Increased ‘weediness’ in the affected area is also common.
If nematodes are present, roots may be stunted, lack lateral roots and may have brown lesions from nematode pruning.
Management strategies for RLN
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 resistant 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. Resistance ratings for P. neglectus and P. thornei for wheat and barley can be found in the current Crop Variety Sowing Guides for WA
- Controlling summer weeds and the green bridge and adopting good plant nutrition
- Building the natural suppressiveness of soil to RLN.
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. It is important to send whole plants, including intact root systems and soil – for both suspect and healthy samples.
PreDicta-B® can test for P. neglectus, P. teres and P. thornei. It is available from SARDI until mid-May.
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: firstname.lastname@example.org
Caption: DAFWA plant pathologist Daniel Hüberli attracted a big audience at the West Midlands Group spring field day demonstration of 2014 rhizoctonia bare patch fungicide trials. Photo: DAFWA.
Daniel Hüberli, DAFWA
08 9368 3836
Sarah Collins, DAFWA
08 9368 3612
Melissa Williams, Cox Inall Communications
042 888 4414
DAFWA AGWEST Plant Laboratories: www.agric.wa.gov.au/plant-biosecurity/agwest-plant-laboratories
PreDicta-B®: www.sardi.sa.gov.au/diagnostic_services/predicta_b or contact: Shawn Rowe, SARDI, 0477 744 305, email@example.com
DAFWA root disease and testing service information: www.agric.wa.gov.au/barley/root-disease-under-intensive-cereal-production-systems
DAFWA MyCrop crown rot: www.agric.wa.gov.au/mycrop/crown-rot-cereals
GRDC Fact Sheet Crown rot in cereals: www.grdc.com.au/GRDC-FS-CrownRotCerealsSW
DAFWA MyCrop Rhizoctonia YouTube: https://agric.wa.gov.au/n/2143
and Taking a Plant Sample: http://youtu.be/_hqjXWEkByg
GRDC Fact Sheet Management to minimise Rhizoctonia disease in cereals: www.grdc.com.au/GRDC-FS-RhizoctoniaSW
GRDC Hot topic: www.grdc.com.au/RhizoctoniaBarePatchWA
GRDC Fact Sheet Plant Parasitic Nematodes: 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
GRDC - The current and potential costs from diseases of wheat in Australia: www.grdc.com.au/DiseasesCostsWheat
GRDC Project Code DAN00175, DAS00122, DAS00123, DAS00125, UWA00152, DAW0021, DAW00174, DAW00212, DAW00201, DAS00137, DAW00209, DAW00157