Stripe rust management during a high-pressure season

By BCG Staff and Contributors
Views

By Hari Dadu, Grant Hollaway, Mark McLean (Agriculture Victoria) and Genevieve Clarke (BCG)

Take Home Messages

  • Early, severe stripe rust pressure caused significant yield (~50 per cent) and quality losses in susceptible wheat varieties when not managed during 2022.
  • At least two foliar fungicide applications at Z31 and Z39 were required to protect grain yield and reduce losses in susceptible varieties.
  • Disease pressure going into the 2023 season will be extreme with carry-over of inoculum from cereal volunteers.
  • Proactive disease management that combines removal of green bridge, variety selection (avoiding susceptible varieties), up front fungicide use (eg. flutriafol on fertiliser) and timely in-crop fungicide use, provides proven sustainable and economic management of stripe rust.

Background

Due to the significant opportunity for stripe rust to survive summer on volunteer cereals (the ‘green bridge’) in northern Australia, rust appeared in Victorian wheat crops earlier than usual in 2022. This early rust onset, along with favourable conditions for disease development, caused a damaging outbreak of stripe rust across the state. Large yield losses due to stripe rust in susceptible wheat varieties occurred where management was inadequate.

Industry reports during the season confirmed strategies of avoiding susceptible cultivars, using up-front fungicides, and timely foliar fungicide applications all helped reduce stripe rust pressure in paddocks. Such circumstantial evidence where available is valuable to growers for managing future stripe rust epidemics.

Severe stripe rust pressure affected two Agriculture Victoria trials at Nullawil in the Mallee that were established to determine the impact and management strategies for Septoria tritici blotch. There was also significant stripe rust within the two unsprayed National Variety Trials (NVT) at Nullawil and Charlton. Stripe rust severity and yield data from the trials has been collected and is presented in this report. The results demonstrate the benefits of using resistant cultivars and timely fungicide strategies against stripe rust during a high-pressure season.

Aim

  • To determine yield loss caused by stripe rust in the Mallee during a high-pressure season.
  • To identify optimal fungicide application timing to manage stripe rust.

Paddock Details

Location: Nullawil

Crop year rainfall (Nov–Oct): 497mm

GSR (Apr–Nov): 384mm

Soil type: Clay

Paddock history: Lentil

Location: Charlton

Crop year rainfall (Nov–Oct): 616mm

GSR (Apr–Nov): 473mm

Soil type: Clay

Paddock history: Lentil

Trial Details

Crop type: Wheat

Treatments: Refer to Table 1

Target plant density: 150 plants/m² 

Seeding equipment: Knife points, press wheels, 30cm row spacing

Sowing date:Nullawil: 4 May (Agriculture Victoria trials), 9 May (NVT), Charlton: 18 May (NVT)

Replicates: Six (Agriculture Victoria trials); unreplicated (NVT)

Harvest date: Nullawil: 15 December (Agriculture Victoria trials), 17 December (NVT), Charlton: 20 December (NVT) 

Trial Inputs

Fertiliser: Trials managed as per best practice reflecting the region and so nutrients are not limiting.

Herbicide/insecticide: Trials kept weed and pest free

Fungicide: Refer to Table 1

Seed treatment/inoculant: Refer to Table 1

Method

1. Unsprayed National Variety Trial: Variety selection

As part of the NVT program funded by GRDC, two unsprayed trials, one each at Nullawil and Charlton. A total of 102 wheat entries without replicates were included at Nullawil and 97 at Charlton. Both trials were managed by BCG in accordance with NVT protocols set by GRDC. Trials were left unsprayed to allow disease development. Visual assessments of stripe rust severity in-season (1–9 scale) and grain yield.

2. Variety selection: Yield loss

Replicated field trials were sown in a split plot design with disease control as the whole plot and variety as the subplot, with six replications (Table 1a). Assessments included scoring for stripe rust in-season, yield and grain quality. 

3. Fungicide timing

Replicated field trials were sown in a randomised complete block design with six replications. Fungicide was applied at different timings (Table 1b). Assessments included scoring for stripe rust in-season, yield and grain quality

Results

1. Unsprayed National Variety Trial: Variety selection

Stripe rust epidemics started considerably earlier than usual in the Mallee during 2022, with the first detection in the first week of August. Conditions favoured disease progress and it spread across the region, resulting in high severity in many crops. This was evident in the NVT at Nullawil and Charlton where stripe rust progressed throughout the season. In the absence of chemical intervention, varieties produced variable responses which were consistent with varietal resistance. Based on the response, varieties were grouped in eight resistance categories ranging from Resistant (R) to Susceptible – Very Susceptible (SVS). Greater severity was found in the SVS varieties at both sites. When the mean yields were aggregated according to the eight resistance categories, varieties demonstrated yields reflective of their resistance to stripe rust (Figure 1 and Figure 2). In general, yield potential of varieties gradually reduced as severity increased. Resistant varieties retained their yield potential while susceptible varieties showed reduced yield potential, demonstrating the benefits of avoiding highly susceptible varieties during high-pressure seasons. 

2. Variety selection: Yield loss

Stripe rust first appeared in Scepter at around tillering and rapidly developed in the maximum disease plots where no control was applied (Table 2). However, the severity varied significantly among varieties, with susceptible varieties Calibre and Scepter recording higher severity (89 per cent) at the milk development stage. This resulted in yield losses of around ~39–50 per cent or ~1.81t/ha. In contrast, severity was significantly lower in resistant or better rated varieties and yield losses amounted to only 0.42–0.86t/ha, highlighting the importance of using resistant varieties during a high-pressure season such as 2022.

Severe stripe rust pressure led to head infection later in the season, causing grain quality to decline in most varieties (Table 3). Resistance to head infection also varied among the varieties along the lines of leaf resistance rating. But Calibre was found highly susceptible compared to Scepter, even though similar severity percentage for leaf was scored. This indicated resistance to head infection is independent of varietal resistance to leaf and hence variety selection should be made with caution. 

3. Fungicide timing

Fungicide applications significantly reduced both stripe rust (leaf ) severity and head infection compared to untreated control (Table 4). The impact of seed treatment is considered insignificant since stripe rust was first noticed at around tillering-flag emergence stage. Sole foliar applications, at Z31 or Z39, were not as effective at reducing severity as two sprays combined at Z31 and Z39. Foliar spray at Z31 protected the crop from primary infection while a follow up spray at Z39 limited the infection spread from top three flag leaves, resulting in yield increase by ~48–51 per cent or 1.16t/ha. A single foliar spray at Z39 following stripe rust detection was the next best treatment with ~33 per cent yield increase and similar effects on head infection and grain quality as the two-spray strategy (Table 5).

Commercial Practice and On Farm Profitability

Rust risk going into the 2023 season will be extreme. The opportunities for rust to survive summer on volunteer cereals (the ‘green bridge’) and infect new crops will be immense due to widespread summer cereal volunteers across eastern Australia. Rust outbreaks are more severe following seasons with widespread volunteers as rust can only survive from one season to the next on living plant material. It can’t survive on seed, stubble or soil.

It is therefore essential that growers take the following steps to reduce their risk:

  1. Remove the green bridge (volunteer cereals) by mid-March
  2. Use a current cereal disease guide to check resistance ratings of varieties, and where possible avoid susceptible varieties
  3. Develop a fungicide management plan, with an emphasis on up-front options such as flutriafol on fertiliser, to provide early rust suppression
  4. Download the StripeRustWM App for iPads and Android tablets to support wheat stripe rust management.

When rust risk is high the benefits from widespread use of up-front fungicide treatments (such as flutriafol on fertiliser) should not be underestimated in providing regional control. Such a practice on all at-risk cereal varieties on an industry-wide scale can greatly reduce rust risk across a district.

Acknowledgements

This research was funded by the Victorian Government (Agriculture Victoria) and GRDC as part of the GRDC projects ‘NVT Pathology Services for Generation of Cultivar Disease Resistance Ratings 2019–2023’ (DJP1905-002SAX) and ‘Epidemiology of Septoria Tritici Blotch in the low and medium rainfall zones of the Southern region to inform IDM strategies’ (DJPR2104_004RTX).

Thanks to Agriculture Victoria’s field crops pathology team at Horsham and the BCG team for technical and scientific support.

Back to top

Become a BCG Member

BCG exists for its members. Research and extension activities are designed to provide members with information and resources that will help them improve the productivity, profitability and sustainability of their farm businesses.

Improve your profitability

Receive the latest research, extension and event news direct to your inbox! For a limited time, receive a free technical bulletin when you subscribe.