Keep up with the latest research information on cereal diseases including root diseases and crown rot. The following papers and key messages were presented at the GRDC Updates across Australia in February and March 2018.
Read the key messages from each paper below and click the paper titles to view the full papers.
Authors: Marg Evans (SARDI), Blake Gontar (SARDI), Hugh Wallwork (SARDI).
Eyespot expression in many areas of South Australia (SA) in 2017 was generally low in cereal crops due to the late start to the season, followed by low rainfall until mid to late tillering. In these areas (or paddocks), eyespot inoculum levels, and so the eyespot risk for 2018, are likely to be reduced. In areas of the state (and in paddocks) which experienced good or normal rainfall, the eyespot risk will depend on inoculum levels in individual paddocks. Consider using a PREDICTA® B test if you are in any doubt about the risk of yield losses from crown rot or eyespot in at-risk paddocks as, given the past two seasons, it will be difficult to predict risks based on paddock history. Be cautious in selecting barley varieties susceptible to net form net blotch (NFNB) as this disease is likely to increase in significance in coming years.
Authors: Alan McKay, Marg Evans, Daniele Giblot-Ducray, Herdina, Katherine Linsell, Tara Garrard, Shawn Rowe, Laura Davies (SARDI), Gupta Vadakattu (CSIRO), Grant Hollaway, Joshua Fanning, Melissa Cook (Agriculture Victoria), Steven Simpfendorfer (NSW DPI)
- Soil-borne diseases most likely to pose the greatest risk to cereal crops in the southern region during 2018 include rhizoctonia root rot, crown rot and root lesion nematodes.
- PREDICTA® B has new tests for ascochyta blight of chickpeas, plus yellow leaf spot and white grain disorder of wheat. Follow sampling recommendations in manual V10. Misplaced PREDICTA® B accreditation numbers can be retrieved by contacting Nigel Percy
- Rhizoctonia root rot symptoms are worse in low rainfall seasons, but net yield losses increase when growing season rainfall increases from 200mm to 400mm in combination with a dry finish. PREDICTA® B can identify paddocks before seeding where losses are likely to occur. To reduce losses: control summer weeds, sow early, use soil openers that disturb soil below the seed, and consider seed treatments. Best protection is achieved by dual streaming fungicide on soil surface above the seed and at the base of the furrow below the seed. Barley is affected more than wheat.
- Crown rot losses are greater in seasons with good winter rainfall followed by moisture stress during spring. Yield loss is highest in durum, followed by wheat and then barley. If growing durum use PREDICTA® B to avoid medium to high crown rot risk paddocks. Select from the best adapted, least susceptible cereal varieties. Sow early within the optimum seeding window, and match nitrogen (N) fertiliser to season potential. In non-cereal phases, grow pulses and oilseeds that achieve early canopy closure to hasten stubble breakdown.
- Root lesion nematode effects on yield vary between seasons. In 2017 at Pinery SA, Pratylenchus neglectus caused yield losses of 0.5t/ha to 1.5t/ha in a range of wheat varieties. Use PREDICTA® B to determine which species are present, then check latest cereal disease variety guide to select the least susceptible of the best adapted varieties. Sow early within the optimum seeding window. When growing non-cereals, check seeding guides to select non-host crops/resistant varieties.
Authors: Greg Platz, Lisle Snyman, Judy McIlroy (DAFQ)
Powdery mildew is a highly variable and ubiquitous pathogen of barley. Powdery mildew is essentially a disease of the vegetative stage in the Northern Region and seldom causes losses greater than 15%. Historically single gene resistances are readily overcome. The resistance gene mlo has remained effective for over 50 years in Europe but has not been widely adopted in Australian breeding programs. Fungicides usually provide very effective control. Resistance to fungicides in powdery mildew is well documented in Western Australia and recorded in eastern Australia. Best management fungicide practices are required to preserve their efficacy.
Authors: Alan McKay (SARDI), Simon Simpfendorfer (NSW DPI), Gupta Vadakattu (CSIRO), Sean Bithell (NSW DPI), Kevin Moore (NSW DPI), Richard Daniel (Northern Grower Alliance), Cassy Percy (USQ), Jo White (USQ), Adam Sparks (USQ), Grant Hollaway (Agriculture Victoria).
Soil-borne pathogens most likely to pose the greatest risk to cereal crops in the northern region during 2018 include crown rot, common root rot and root lesion nematodes. PREDICTA®B has added new tests for ascochyta blight and phytophthora root rot of chickpeas, yellow leaf spot and white grain disorder of wheat, fusarium stalk rot of sorghum, charcoal rot of summer crops and arbuscular mycorrhizal fungi (AMF). Frequently more than one soil-borne disease exists within a paddock with the interaction between pathogens (e.g. Pratylenchus thornei and crown rot) exacerbating losses. PREDICTA B is assisting pathologists to understand these interactions to advise growers on management options to limit the impact of these disease complexes.
Authors: Greg Platz, Lisle Snyman, Clayton Forknall (DAFQ)
Spot form of net blotch (Pyrenophora teres f. maculata) is the most widespread and conspicuous disease of barley in Australia. It is the target of many of the fungicide applications made to barley crops because it is so conspicuous and because most commercial varieties are susceptible or worse. Maximum losses to spot form net blotch (SFNB) may reach 30% in very susceptible barley varieties. Losses are influenced by varietal susceptibility, severity of the disease, duration of the epidemic and environment. Instances of maximum disease development are rare and losses in susceptible varieties, even in favourable seasons, are more likely to be in the order of 20%. Varieties with a resistance rating of moderately susceptible or better are necessary to provide useful protection against SFNB.
Authors: Andrew Milgate and Brad Baxter (NSW DPI)
The frequency of winter cereals in a rotation influences build-up of crown rot inoculum within paddocks. Risk of losses in grain yield can be minimised by monitoring inoculum levels over time and implementing management strategies to reduce them. Crown rot can have negative impacts on grain quality and gross margins even without observing obvious symptoms and grain yield losses. Significant reductions in crown rot inoculum levels can be achieved by growing two consecutive non-host crops.
Authors: Lisle Snyman, Greg Platz, Clayton Forknall (DAFQ)
Barley and wheat varieties are categorized into resistance categories through the National Variety Trial (NVT) disease screening process. The resistance ratings are assigned by pathologists collecting group data conducted annually. Barley varieties differ in yield loss response to net form net blotch (NFNB) across resistance ratings. The most significant yield losses were incurred in varieties rated susceptible to very susceptible. Varieties at the susceptible end of the rating scale contribute to inoculum pressure and increase the risk of breakdown of resistance in other varieties. Results from yield response curve trials assist in validating National Variety Trial disease resistance ratings by combining losses in yield and quality.
Authors: Greg Platz, Lisle Snyman, Ryan Fowler (DAFQ)
Net form net blotch (NFNB) pathotypes able to infect barley varieties Commander and Compass have increased in recent years. Prolonged and widespread cultivation of any barley variety will allow NFNB to adapt to that variety. Sowing barley on barley, especially successive crops of the same variety, increases the risk of NFNB and favours the selection of virulence in the pathogen for that variety. Environmental conditions play a major role in the development of NFNB, with wet conditions favouring infection and spread of the disease. NFNB can be spread via the sowing of infected seed that has not been treated. NFNB is best controlled by crop rotation, sowing of varieties with a disease rating of moderately susceptible or better, treating seed prior to sowing, regular monitoring crops for NFNB and timely application of a registered foliar fungicide before disease becomes well established.
Characterising soil borne disease risk in the eastern wheat belt of Western Australia and national significance of major diseases
Authors: Kylie Chambers (DPIRD), Alan McKay (SARDI), Daniel Huberli (DPIRD), Marg Evans (SARDI), Gupta Vadakattu (CSIRO), Grant Hollaway (Agriculture Victoria).
Pathogens of important diseases of cereals frequently detected in a recent survey of the eastern wheat belt of Western Australia in 2017 included:
- Crown rot (62% of samples tested)
- Root lesion nematodes (79% of samples tested)
- Rhizoctonia root rot (49% of samples tested)
The impact of root diseases can be difficult to recognise and targeted testing of paddocks can identify situations of increasing or high risk. While pathogen levels detected by PREDICTA® B are an important indicator of potential disease risk, seasonal conditions, crop choice and management practices are also important factors in determining how much disease actually develops. The lack of profitable non-cereal rotation options, and the use of stubble retention to conserve moisture, can make it difficult to manage root diseases, particularly crown rot. While reducing inoculum levels is desirable, research in this region may need to include exploring improved non-host rotational crops and selecting well adapted cereal varieties that can perform in the presence of root disease, combined with cropping practices that reduce moisture and heat stress during grain fill.
Oats, pastures and other legumes – Are rotations offering breaks for root lesion nematodes or crown rot?
Authors: Sarah Collins, Carla Wilkinson, and Daniel Huberli (DPIRD).
Some pasture crops are effective for reducing root lesion nematode (RLN; P. neglectus and P. quasitereoides) populations in a season, but others can greatly increase RLN populations. Oats are not a good break crop for reducing P. neglectus or crown rot levels in a paddock. However, for P. neglectus, oats are less susceptible than wheat and variety choice makes a difference. For crown rot, oats can increase inoculum levels similar to wheat. Fusarium pseudograminearum caused average yield losses of 4% in oat varieties tested, which is four times lower than check wheat varieties Mace and Emu Rock which had an average yield loss of 17%.