Take Home Messages
- Applying Moddus® Evo @ 400mL/ha or Moddus® Evo @ 200mL/ha with Errex®750 @ 1300mL/ha at GS31 significantly reduced plant heights in comparison to the control (no PGR).
- No yield responses were observed from different PGRs in comparison to the control, despite some minor lodging occurring in the durum wheat crop at harvest.
- Consider agronomic lodging risks and the long-range seasonal outlook before stem elongation when deciding whether to apply PGRs as not every season will be suitable in the Wimmera, Mallee and North Central regions.
Aim
To evaluate the use of PGRs in the canopy management of durum wheat.
Background
Under favourable seasonal conditions cereal crops, particularly durum wheat, can grow very tall and accumulate a lot of biomass, which increases the risk of lodging and can result in reduced yields and harvest headaches. One potential management method is the application of plant growth regulators (PGRs).
PGRs have been available for several years but their results can be variable and in some cases have a negative effect on yield (Jones 2014). In the scientific literature, applying PGRs at stem elongation (GS30–32) in cereals has been reported as the most effective approach to reduce plant height (Acuna et al. 2015).
In response to the significant lodging that impacted crops in 2022 and the lack of information around the use of PGRs in durum wheat, BCG conducted a trial at Wallup.
Paddock Details
Location: Wallup
Crop year rainfall (Nov–Oct): 311mm
GSR (Apr–Oct): 177mm
Soil type: Clay
Paddock history: Lentil
Trial Details
Crop type/s: Durum wheat: Aurora
Treatments: 1. Control (no PGRs applied)
2. Moddus® Evo @ 200mL/ha (GS31)
3. Moddus® Evo @ 400mL/ha (GS31)
4. Moddus® Evo @ 200mL/ha and Errex®750 @ 1300mL/ha (GS31)
5. Moddus® Evo @ 100mL/ha and Errex®750 @ 650mL/ha (GS30 & GS32)
Target plant density: 140 plants/m²
Seeding equipment: Knife points, press wheels, 30cm row spacing
Sowing date: 3 May 2023
Replicates: Four
Harvest date: 17 December 2023
Trial average yield: 6.0t/ha
Trial Inputs
Fertiliser: Granulock Supreme Z + Flutriafol (400mL/100 kg) @ 60kg/ha at sowing and 270kg/ha of urea applied as a split application (GS13, GS31).
Weeds, pests and diseases were managed as per best practice.
Method
A replicated field trial was sown using a complete randomised block trial design. Assessments included establishment counts, plant heights (three random measurements throughout plot), lodging scores, grain yield and grain quality. The PGR treatments were applied on 26 July 2023 (GS30), 1 August 2023 (GS31) and 9 August 2023 (GS32)
Method
The trial established well, averaging 96 plants/m². When plant heights were measured on 22 September 2023 at GS55 the high rate of Moddus® Evo at 400mL/ha, and Moddus® Evo at 200mL/ha and Errex® 750 at 1300mL/ha applied as a single application at GS31 had significantly lower plant heights compared to other treatments (Figure 1). Interestingly, the split application of Moddus® Evo and Errex® 750 at GS30 and GS32 did not result in a difference in plant height compared to the control but the single application at GS31 did (Figure 1). This is inconsistent with trial results conducted by FAR Australia in 2020 (FAR Australia 2021). A possible explanation may be that the crop was moisture stressed at the time of application, and the late tillering to GS32 development phase progressed at a rapid rate. Crops that develop too quickly are rarely suited to a split application.
There was no lodging in the trial on 22 September 2023, however at the time of harvest (17 December 2023) some minor lodging was noted. Scores were carried out and the control scored slightly higher (more severe lodging) than the PGR treatments (Figure 2). There were no differences in the average lodging scores between the different PGR treatments.
No differences were observed between the treatments for both yield and grain quality parameters tested (data not presented). This was as expected considering the little lodging recorded in the trial. In terms of quality, the trial averaged DR2 with 12.5 per cent protein, 78.63kg/hL test weight and 3 per cent screenings.
Commercial Practice and On Farm Profitability
The application of a PGR is often considered where the risk of crop lodging is high and crops are likely to yield 4t/ha or greater (Jones 2014). This was the case at Wallup with a yield potential of 7t/ha at the start of the season. however as the year unfolded rainfall distribution was skewed towards autumn and early winter (Figure 3)
The lack of late winter and spring rainfall contributed to minimal lodging being observed in the durum wheat crop and thus no yield benefits were seen from the application of PGRs. This highlights the challenges for growers in the Wimmera (and sometimes Mallee and North Central) environments where higher yields (>4t/ha) are possible but not every season will be conducive to crops lodging in spring.
So how to decide whether and when to apply a PGR? Some of the agronomic influences that can increase or decrease the lodging risk of a crop are highlighted in Table 1. Consider these along with the long-range seasonal outlook before the crop reaches stem elongation to help guide the decision-making process.
Product and application costs are also something to keep in mind when considering their use. PGR products can cost in the realm of $79.30/L with an application cost of around $15/ha (FAR Australia, 2022).
References
Acuna T., Merry A., Carew A., and Leith, P., 2015, Building Productive, Diverse and Sustainable Landscapes Proceedings of the 17th Australian Agronomy Conference 2015 ‘Plant growth regulator use in broad area crops’, <https://figshare.utas.edu.au/articles/conference_contribution/Plant_growth_regulator_use_in_broad_acre_crops/23094689>, [accessed 17 January 2024].
Ayliffe E., 2023, IREC Irrigated Durum Trial 2022, Summit Ag Agricultural Research, <https://irrigationfn.com.au/wp-content/uploads/2023/04/IREC-Durum-PGR-Trial-Report-Final.pdf>, [accessed 17 January 2024].
FAR Australia, 2021, Optimising irrigated grains, ‘Key Learnings (Durum): 2020 and 2021’ <https://irec.org.au/wp-content/uploads/220324_OIG-Key-Learnings-DURUM_final-002.pdf> [accessed 19 January 2024].
FAR Australia,. 2022, Optimising irrigated grains, ‘Key Learnings: 2020 and 2021’, https://irec.org.au/wp-content/uploads/220324_OIG-Key-Learnings_final-002.pdf, [accessed 19 January 2024]
Jones D. 2014, Plant growth regulators, GRDC Update Paper, <https://grdc.com.au/resources-and-publications/grdc-update-papers/tab-content/grdc-update-papers/2014/07/plant-growth-regulators>, [accessed 27 October 2023].
Acknowledgements
This research was funded by the Southern Australia Durum Growers Association (SADGA) and BCG members through their membership.
Thank you to Nick Poole, FAR Australia, for providing technical advice for this article.
We thank the Gregson family for hosting this trial.
