Management of crown rot in southern NSW farming systems

Take home messages

  • The frequency of winter cereals in a rotation influences the 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.

ɸExtra technical comment by Protech Consulting Pty Ltd

Background

This paper is a summary of the research conducted to date under the National Crown Rot Management Program - Southern Component of DAN00175, consisting of results from:

  1. Longitudinal surveys of soil and stubble borne pathogens in southern NSW (sNSW).
  2. Crown rot non-host crop rotation, duration and crop sequence trial.
  3. Crown rot varietal yield loss trials undertaken from 2011-2017.

Crown rot is estimated to cause $79 million annually in economic losses to Australian cereal growers (Murray and Brennan, 2009). Fusarium pseudograminearum and F.culmorum are the two most common casual agents of this disease. The crown rot fungi are soil and/or stubble borne fungal pathogens which restrict the flow of water and nutrients to developing heads when moisture or heat stress occurs during the critical grain filling stage. This can result in pinched grain or heads with no grain, otherwise known as ‘whiteheads’. Crown rot fungi infect winter cereals including barley, bread wheat, triticale and durum wheat, in order of decreasing tolerance to the pathogen (Milgate, Goldthorpe and Baxter, 2017 p. 139). The crown rot fungus can also survive in a range of grass weed hosts including ryegrass, wild oats and annual phalaris.

Crown rot is favoured by wet, cool winters and dry, hot spring conditions. It may be identified early in the growing season as browning of the outer leaf sheaths at the base of infected tillers, stunted yellow plants or single dead tillers. More reliable identification can occur in periods of moisture stress. Typically, honey coloured stem browning extending from the sub-crown internode upwards to the first or second node on infected stems occurs.

As opposed to take-all, where all tillers on a single plant will express whiteheads, crown rot will cause scattered whiteheads across the paddock with individual tillers on plants affected.  Grain yield loss and downgrade of grain quality can still occur without the expression of whiteheads (Milgate et al. 2017 p. 139).

The prevalence of crown rot in southern NSW farming systems has increased due to the adoption of ‘no-till’ cropping systems and the most common rotation being based on tight cereal and canola sequences. The presence of crown rot, along with other crown and root diseases, in southern NSW farming systems creates ‘disease complexes’ which have negative impacts on grain yield, protein and quality.

These disease complexes can be managed through an integrated approach which focuses on monitoring and setting in place rotations which act to reduce the risk of losses across the whole farming system. Besides crop rotation, other management practices that can be implemented involve effective weed management programs to reduce grass weed hosts in-crop and fallow situations, inter-row sowing between cereal stubble, early sowing within a variety’s ideal sowing window and ensuring adequate nutrition for the season, particularly zinc.

This paper brings together research of several elements of the integrated management of crown rot for growers to consider implementing.

Method

PreDicta B™ analysis underpins the methodologies used to assess soil and stubble borne pathogen levels in the experimental plots and paddock surveys. PreDicta B™ estimates selected soil and stubble borne pathogen levels using DNA assays developed by the South Australian Research and Development Institute (SARDI).

The individual methodologies for the paddock survey, non-host crop rotation, duration and sequence trial, along with the crown rot varietal yield loss trial, are discussed here.

Longitudinal survey of soil and stubble borne diseases in southern NSW farming systems

There were 93 paddocks in the survey set covering high, medium and low rainfall zones across southern NSW from 2014 to 2017. The paddocks were assessed in the cereal phase only, with the yearly rotation recorded on each. The paddock survey sampling is providing ‘real world’ data to support findings on trial work currently being undertaken.

Soil and stubble samples are collected, starting at a permanent GPS location, collecting from the centre moving outwards in a spiral pattern. Ten soil cores and 10 pieces of stubble are collected at the points along the spiral. The samples are bulked, homogenised and a sub-sample taken for analysis. The sub-sample is comprised of 500g of soil and 30 random pieces of cereal stubble 4­–5cm long, ensuring the crown was present on the stubble (Milgate et al. 2017 p. 139). The pre-sowing samples were collected in April of the sowing year and the post-harvest samples collected in January of the following year. The sub-samples are then sent off for analysis by SARDI.

Non-host crop rotation, duration and sequence trial

The trial is a randomised paired split plot trial with five replicates consisting of 600 plots in total, with 120 different treatments over the five years starting in 2014 and finishing in 2018. The trial examined a one or two year non-host crop cycle, different combinations of crop sequences, fungicide treatments and controls. A non-host crop is anything other than a cereal. There are three wheat variety treatments — very susceptible (VS), susceptible (S) and tolerant (T). Other treatments include one barley treatment, along with four non-host crops including canola, lupin, field pea and a vetch/wheat mix to simulate a hay cut. The term tolerant (T) has been used instead of resistant, as there are currently no fully resistant varieties to crown rot, but varieties differ in their tolerance to the pathogen. The methodology to assess pathogen levels in this trial is the same method used in the paddock survey — PreDicta B™. The collection method is based on a random sample from plots instead of a structured spiral pattern as used at the paddock scale.

The treatments displayed in Figure 4 of this paper include two up front fungicides for comparison. These were Rancona® Dimension (ipconozole 25g/L and metalaxyl 20g/L applied to wheat seed at a rate of 320mL per 100kg) and Jockey® Stayer®ɸ (fluquinconazole 167g/L applied to wheat seed at a rate of 450mL per 100kg).

ɸJockey® Stayer® is not registered to control Crown rot in wheat at this rate. This rate is used for research purposes only. Commercial application of this product must adhere to label rates.

Table 1. Treatment details from rotation sequence and duration experiment shown in Figure 4.

Year

Treatment name

Details

2014

Durum

Caparoi

2015

Canola

ATR-Gem

2016

Wheat-Tol

Emu Rock

Wheat-Tol+Jockey

Emu Rock +Jockey® Stayer®

Wheat-Tol+Rancona

Emu Rock +Rancona® Dimension

Wheat-S

LongReach Lincoln

Wheat-S+Jockey

LongReach Lincoln +Jockey® Stayer®

Wheat-S+Rancona

LongReach Lincoln +Rancona® Dimension

Pea

PBA Oura

Lupin

Mandelup

Crown rot varietal yield loss trial

The yield loss trials consisted of ‘plus crown rot’ and ‘minus crown rot’ treatments with four replicates assessing 17 wheat and eight barley varieties. The crown rot ‘plus’ treatment consists of viable wheat or barley seed sown with sterilised durum seed inoculated in the laboratory with multiple isolates of the crown rot fungus. The crown rot inoculated seed is sown at a rate of two grams per metre of trial row. Yield reduction caused by crown rot is assessed at harvest by comparing the grain weights between the plus and minus treatments.

Pathogen levels within plots were determined by PreDicta B™ analysis of 30 randomly selected pieces of stubble from individual plots which were bagged with 500g of sterilised soil. This identifies if contamination occurs between treatments or background levels of crown rot are naturally occurring and those affected plots removed from the analysis.

Results and discussion

Longitudinal survey of soil and stubble borne diseases in southern NSW farming systems

A trend consistently appearing from the paddock survey data is the prevalence of crown rot in southern NSW farming systems. Table 2 displays the percentage of post-harvest sampled paddocks which were infected with crown rot from 2014 to 2016. The high incidence of crown rot indicates that inoculum levels are present before sowing and developing during the growing season. The inoculum is surviving over the summer in the stubble and soil, ready to infect cereal crops in the following year. Sampling post-harvest gives the flexibility to make management decisions, such as changing cereal type or crop type for the following year if inoculum levels are found to be high and a risk to the next cereal crop within the rotation sequence.

Table 2. Prevalence of crown rot in the southern NSW paddock survey, 2014 to 2016 post-harvest sampling.

Year

No. of paddocks sampled

Percentage (%) of paddocks with crown rot fungi present (post harvest)

2014

41

73

2015

34

91

2016

39

85

The survey data collected from 2014 to 2017 is showing strong trends relating to pre-sowing crown rot inoculum levels when comparing the duration of non-host crops between cereal crops (Figure 1) and the effects of the previous crop on pre-sowing levels of inoculum (Figure 2).

The survey data collected from 2014 to 2017 is showing strong trends relating to pre-sowing crown rot inoculum levels when comparing the duration of non-host crops between cereal crops.

Figure 1. Effect of the number of years since non-host crops on pre-sowing levels of crown rot (F. pseudograminearum + F. culmorum) prior to sowing 2014 to 2017 (number of paddocks = 147) measured by PreDicta B™ analysis. Log risk levels: Below detection limits = <0.6. Low = 0.6 –<2.0. Medium = 2.0 –<2.5. High = ≥ 2.5 for bread wheats in southern NSW.

Figure 1 shows the pre-sowing increase in inoculum and risk levels associated with sowing cereal on cereal. As the number of years between sowing non-host crop increases, the pre-sowing crown rot inoculum significantlyincreases. Essentially, a cereal crop sown after a non-host crop (0 years) has a close to below detectable limits (BDL) risk, translating to a 0–5% potential yield loss (McKay et al. 2015). After three years of continuous cereal, or two years since a non-host crop, the risk level is deemed medium and relates to a potential 5-30% yield loss (McKay et al. 2015) under the right conditions such as moisture or heat stress during grain filling. Losses of this magnitude and higher were observed in the 2017 Condobolin crown rot yield loss trial (Figure 6).

The survey data collected from 2014 to 2017 is showing strong trends relating to pre-sowing crown rot inoculum levels when comparing the effects of the previous crop on pre-sowing levels of inoculum.

Figure 2. Previous crop effects on the background levels of crown rot (F. pseudograminearum + F. culmorum) prior to sowing 2014 to 2017 measured by PreDicta B™ analysis. Log risk levels: Below detection limits = <0.6. Low= 0.6–<2.0. Medium= 2.0–<2.5. High= ≥ 2.5 for bread wheats in southern NSW.

The effect that the previous crop can have on the pre-sowing levels of crown rot inoculum is shown in Figure 2. The majority of the data is located in the canola and wheat columns — this is typical of southern NSW farming systems which sow these crops in tight rotations. The issue that arises with these types of rotations is that a single break of canola away from cereal is not necessarily reducing crown rot inoculum to a safe level to sow a cereal crop without risk of significant yield losses in the following year. On average, the canola paddocks reduced the inoculum levels more compared to wheat. Wheat had approximately 50% of the paddocks fall into the medium to high risk category for yield loss. However, a concerning result is the number of canola paddocks that fell into the medium to high risk category which could result in between 5–60% yield loss (McKay et al. 2015). This indicates that sowing a single non-host crop may not allow enough time to reduce disease levels. The other non-host crops show lower inoculum levels; however, they do not have enough data points to draw any solid conclusions, but are broadly in line with the findings of other published research.

Figure 3. Crown rot (F. pseudograminearum + F. culmorum) levels of four paddocks during the growing season from pre-sowing to post-harvest in 2014 to 2016 and pre-sowing 2017. Log risk levels: Below detectable limits = <0.6, low= 0.6–<2.0, medium= 2.0–<2.5 and high= ≥ 2.5 for bread wheats in southern NSW.

Figure 3. Crown rot (F. pseudograminearum + F. culmorum) levels of four paddocks during the growing season from pre-sowing to post-harvest in 2014 to 2016 and pre-sowing 2017. Log risk levels: Below detectable limits = <0.6, low= 0.6–<2.0, medium= 2.0–<2.5 and high= ≥ 2.5 for bread wheats in southern NSW.

Knowing the risk level and how a particular paddock behaves is critical to making management decisions to maximise yields and economic returns. Not all paddocks will behave the same way during inoculum build-up and depletion as can be seen in Figure 3. The paddock survey covers a large geographical area of southern NSW and therefore samples across different topographical, climatic and agronomical boundaries. Paddocks 3, 6 and 33 in Figure 3 are based on similar rotations, but show very different inoculum behaviour over time. This may be accounted for by interactions between grower management decisions, pathogen and abiotic factors. Paddock 33 is what would be considered a ‘typical’ steady build-up of crown rot, while Paddock 3 is ‘atypical’ of crown rot build-up when sowing continuous cereals. Paddock 15 differs to the other paddocks in rotation. This paddock demonstrates what sowing a non-host crop for two years can do to reduce inoculum levels from a high risk to low risk.

Effective methods for inoculum reduction through crop type and sequence

Maximising inoculum reduction with optimal profitability is being investigated in this trial. The trial is in its fourth year and is providing insight relating to the importance of rotations and the way they influence inoculum behaviour.

Log risk levels: Below detectable limits= <0.6, low= 0.6–<2.0, medium= 2.0–<2.5 and high= ≥ 2.5 for bread wheats in southern NSW.  Seed treatments: Rancona® Dimension (Ran) and Jockey® Stayer® (Jock).

Figure 4. Crown rot inoculum (F. pseudograminearum + F. culmorum level behaviour in the Wagga Wagga crop rotation and sequence trial when comparing one and two year non-host crop rotations. Log risk levels: Below detectable limits= <0.6, low= 0.6–<2.0, medium= 2.0–<2.5 and high= ≥ 2.5 for bread wheats in southern NSW.  Seed treatments: Rancona® Dimension (Ran) and Jockey® Stayer® (Jock).

The effect of introducing a one or two year non-host crop into the rotation on inoculum loads is demonstrated in Figure 4. The eight treatments displayed had the same rotation in 2014 (wheat) and 2015 (canola), but different crop rotations in 2016, creating a one or two year break from a cereal crop. The lupin and pea crops sown in 2016 greatly reduced the inoculum loads to approximately log10 2.40 (250 pgDNA/per gram of soil) or medium risk, as compared to sowing a wheat crop which ranged from log10 3.70 - 4.10 (4700 – 14000 pgDNA/per gram of soil) or high risk. Under the right climatic conditions, medium risk translates to a potential 5–30% yield loss and high to 15-60% yield loss (McKay et al. 2015). This demonstrates the importance of using non-host crops to reduce inoculum levels for two years.

The Rancona® Dimension seed treatment was added to determine its ability to suppress crown rot infection under high disease pressure. Take-all, along with crown rot, is present at the trial site. To account for compounding effects it may have on yields, an additional seed treatment of Jockey® Stayer® was added. This combination of root diseases accurately depicts the disease complexes frequently facing cereal growers in southern NSW.

Inoculum levels fell across all treatments shown in Figure 4 during 2016, except for Wheat-S +Ran. Despite the reduction, all wheat treatments for 2016 showed the levels of inoculum remained above log10 3.70 or high risk. This level is regarded as very high and would cause significant yield loss and grain quality degradation under climatic conditions conducive to the expression of crown rot (i.e. hot and dry during grain filling).

The importance of choosing a more tolerant or resistant variety is illustrated in Figure 4. There is an increase of inoculum by the susceptible, Wheat-S, treatment compared to the more tolerant, Wheat-T treatment.   Wheat and barley commercial varieties do differ in their tolerance to crown rot. This has been demonstrated by crown rot varietal yield loss trials which will be discussed here.

Results from the paddock survey data, the crown rot non-host crop rotation, duration and sequence trial, support the principle that a two year non-host crop break can reduce inoculum levels to a lower point than sowing a single year of a non-host crop.

What this trial will help reveal is whether: 1) A crop type or a certain crop sequence, such as either peas-canola or canola-peas, will cause a greater reduction in crown rot levels than the other, and 2) does it make a difference or is it just the break length that is key? To date, the crop type that has shown the most significant reduction of crown rot inoculum levels in the trial is field peas.

Crown rot varietal yield loss trial

Since 2011, crown rot yield loss trials have been conducted at Wagga Wagga, Cowra and/or Condobolin research stations, totaling 12 trials. It has become apparent from these trials that there are barley and wheat varieties which perform better in the presence of crown rot and appear more tolerant. Barley, rather than wheat, is the higher yielding cereal type in the presence of crown rot infection. One of the reasons for this is due to barley being earlier maturing and avoiding the full effects of moisture stress during grain filling. If a cereal must be grown in a high crown rot risk situation, barley will usually experience lower grain yield losses than wheat. However, barley will still maintain or increase crown rot inoculum levels, result in reduced grain quality and will not address the underlying disease pressure.

Throughout the duration of the yield trials, there have been wheat varieties that display higher yield and lower yield losses in the presence of crown rot when compared to other varieties in the trials. Consistently from 2011 to 2017, Emu Rock, Suntop, Waagan, LongReach Merlin and LongReach Trojan have had higher grain yields than other wheat varieties in the presence of crown rot. More recently, newer varieties have been added into the trial (2016 and 2017) and of these newer varieties, Sceptor, Corack, and Beckom have had higher grain yield compared to the other wheat varieties tested in the presence of crown rot infection.

Barley varieties, Compass, Hindmarsh and Commander have produced higher grain yields when compared to other barley varieties in the presence of crown rot through the 2011 to 2017 trials. More recently, 2016 and 2017, the addition of newer varieties has seen LaTrobe and Rosalind produce yields higher than the other tested barley varieties in the presence of crown rot.

If crown rot risk is high and a cereal must be grown, the current advice is that a grower selects a variety that is best suited to their environment agronomically, regardless of crown rot tolerance. However, if there are two or more suitable varieties, the more tolerant one should be chosen. An example of this can be seen below in Figure 5 and Figure 6. Bass is considered suitable in a medium to high rainfall zone. At Condobolin in 2017, Bass yielded the lowest and had the greatest yield loss of 35% (Figure 5), between the plus and minus treatments (data not shown). Being a longer season variety, it struggled to perform in a short season environment and it encountered moisture and heat stress during grain filling. This confirms the recommendation of choosing an agronomically suitable variety first despite the crown rot tolerance.

At Wagga Wagga, like at Condobolin, Bass yielded the lowest of the barleys (data not shown). However, the overall yield difference between Bass and other varieties was substantially smaller, as it was grown within its preferred environment. Further to that, the yield difference between the Bass plus and minus treatments was 6% (Figure 6), as moisture and heat stress was not as severe as at the Condobolin site during grain filling in 2017.

A variety selection of LaTrobe or Hindmarsh, which are more commonly grown at Condobolin, would increase yields and reduce crown rot losses. This further displays the importance of variety selection for a particular environment.

Figure 5. Grain yield reduction between plus crown rot and minus crown rot treatments for eight barley and 17 wheat varieties at the Wagga Wagga Agricultural Institute, 2017.

Figure 5. Grain yield reduction between plus crown rot and minus crown rot treatments for eight barley and 17 wheat varieties at the Wagga Wagga Agricultural Institute, 2017.

Figure 6. Grain yield reduction between plus crown rot and minus crown rot treatments for eight barley and 17 wheat varieties at the Condobolin Agricultural Research and Advisory Station, 2017.

Figure 6. Grain yield reduction between plus crown rot and minus crown rot treatments for eight barley and 17 wheat varieties at the Condobolin Agricultural Research and Advisory Station, 2017.

Crown rot can affect crop profitability, not just through grain yield losses, but through reduced grain quality: increased screenings, test weight reductions, retention reductions and variation in protein. These factors combine to downgrade grain quality and pricing, adding a ‘multiplier’ effect to any reduced yield. Analysis on the 2015 Wagga Wagga crown rot yield loss trial found that the figure ($) lost per hectare varied between varieties depending on yield, tolerance and grain quality downgrades (Milgate and Baxter 2015, p. 159).

On average, across the 18 varieties, $78.51 per hectare was lost due to yield reduction and grain quality downgrades (Milgate & Baxter 2015, p. 159). The majority of the varieties lost $20-$80 per hectare with Commander most severely penalised at $288.60. This was due to a combination of yield losses and downgrading grain quality from malt to feed grade (Milgate and Baxter 2015, p. 160).

Yield losses and downgrades in grain quality can occur without obvious crown rot symptoms such as stem browning and whiteheads. More importantly, downgrades in grain quality can occur without observing yield losses, indicating that an economic impact can occur without knowing there is an underlying issue.

Conclusion

Management of crown rot in farming systems is a difficult task. There is no easy option and the issue must be managed culturally and through an integrated approach. Quite often there are one or more soil and stubble borne diseases present in a paddock which can add to crown rot yield losses and grain quality downgrading. Crown rot can cause yield losses without obvious symptoms and cause grain quality downgrades without yield losses being observed.

The keys to managing crown rot include the ability to assess risk, paddock rotations that have two years of non-host crops or have flexibility in paddock rotations to implement two year non-host crops if crown rot inoculum levels warrant it, effective weed management programs to reduce grass weed hosts in-crop and fallow situations, inter-row sowing between cereal stubble, early sowing within a variety’s ideal sowing window and ensuring adequate nutrition for the season, particularly zinc. Also, select the more tolerant cereal type or variety to crown rot that is best suited to your region. There are seed fungicide treatments available for the suppression of crown rot, however they have shown little efficacy as a single management tool and must be used as a part of an integrated management approach.

Sowing two non-host crops in succession has been demonstrated to significantly reduce crown rot inoculum levels. The benefits of successive non-host crops are two-fold including the ability to use two control opportunities for problem weeds and the ability of legumes to fix nitrogen which can reduce nitrogen costs in a following cereal crop.

Useful Resources

Crown rot in winter cereals

NSW DPI southern trial results

NSW DPI southern NSW research results

NSW DPI winter crop variety sowing guide

References

McKay A, Mayfield A, Rowe S, eds, 2015. Broadacre soilborne disease manual: PreDicta B™ DNA soilborne disease DNA tests. South Australia: SARDI.

Milgate A and Baxter B, 2015, 'Crown rot variety trials- southern NSW 2015', NSW Department of Primary Industries Southern NSW research results 2015, pp. 158-160

Milgate A, Goldthorpe A, and Baxter B, 2017, 'Southern NSW paddock survey- 2014-2016', NSW Department of Primary Industries Southern NSW research results 2017, pp. 139

Murray, GM & Brennan, PJ   2009, 'The Current and Potential Costs from Diseases of Wheat in Australia'. ACT: GRDC

Acknowledgements

The research undertaken as part of this project is made possible by the significant contributions of producers through trial co-operation, and the authors would like to thank them for their continued support. This project is co-invested by the NSW Department of Primary Industries and Grains Research & Development Corporation and the authors would like to thank Michael McCaig, Tony Goldthorpe, Tim Green, Ian Menz and Daryl Reardon. Thank you to the agronomists who facilitate access to their clients’ paddocks and to their clients for being so willing to work with us.

Contact details

Andrew Milgate
Wagga Wagga Agricultural Institute
Pine Gully Rd Wagga Wagga NSW 2650
02 69381990
andrew.milgate@dpi.nsw.gov.au

Brad Baxter
Wagga Wagga Agricultural Institute
Pine Gully Rd Wagga Wagga NSW 2650
02 69381990
brad.baxter@dpi.nsw.gov.au
@BradBaxter1985
@NSWDPI_Agronomy

GRDC Project Code: DAN00175,