Project title: NGN Validating the use of plant growth regulators to manage excessive growth in barley in Northern Region warm growing environments (2022-24, AMP2205-004RTX).  Methodology: Seven barley PGR trials were run in 2022-23 at a range of locations in northern NSW. In 2022, three trials assessed PGRs Moddus Evo® (250 g/L Trinexapac-Ethyl) and ethephon (Promote® Plus 900, 900 g/L Ethephon) and a range of use patterns across 4 barley varieties. Following high levels of lodging in 2022, four trials in 2023 quantifed the impact of PGR treatments on different varieties, times of sowing and nitrogen levels.   Four varieties – Leabrook, Laperouse, Planet, Maximus CL – were selected to represent the range of lodging susceptibilities in commercial barley varieties. Moddus Evo® and ethephon use patterns were tested to allow for early and late control of barley biomass production as well as bounce back, where compensatory growth occurs under favourable conditions following a PGR application (Table 1). Table 1. PGR use patterns tested on dryland barley in 2022 and 2023   Application 1 Application 2 PGR Treatment Name PGR Rate (ml) GS PGR Rate (ml) GS Moddus 31 Moddus Evo® 400 31       Moddus 300 @ 31 Moddus Evo® 300 31       Moddus 37 Moddus Evo® 400 37       Moddus 31 + 37 Moddus Evo® 400 31 Moddus Evo® 400 37 Ethephon 41 Ethephon* 400 41       Ethephon 45 Ethephon* 400 45       GS=Growth Stage; 900 g/L Ethephon In 2022, the impact of PGR treatments (n=6) on four barley varieties were tested at three locations in northern NSW (Table 2 and Table 3). 1.    At Boomi and Gurley a variety (n=4) by PGR strategy (n=5) full factorial plot trial was established. Due to high rainfall and subsequent waterlogging the trial planted at Boomi failed to establish. 2.    At Tulloona a trial was established to replace the failed Boomi trial. PGR treatments (n=5) were applied over a commercial crop of Planet barley in a randomised complete block design. 3.    At Spring Ridge, a partial factorial experiment assessing varieties (n=4) was established with 6 PGR treatments. In 2023 trial sites were established at Boomi, Gurley, Pallamallawa and Breeza. 4. At Boomi full replicated randomised incomplete block design trials assessed the impact of time of sowing (n=2, early and mid time of sowing) and PGRs (n=6) for four barley cultivars. For the first time of sowing, PGRs (n=6) were applied to four varieties; Leabrook, Laperouse, Planet and Maximus CL, at the second time of sowing PGRs were only applied to lodging susceptible variety Leabrook. 5. At Gurley, the same trial was repeated as describe above for Boom 6. At Breeza, the four barley cultivars were tested with six PGR treatments with one time of sowing only. 7. At Pallamallawa, Leabrook was planted with four nitrogen rates (0, 75, 150 and 250 kg N/ha) applied as urea-N and six PGR treatments were applied. This trial failed due to residual herbicide damage and thus the results from this trial are not presented in this report. Consequently, yield responses to PGR treatment under a range of nitrogen levels was unable to be captured in this project. Seasonal conditions in 2022 and 2023 differed markedly for both in-crop temperatures and rainfall. In 2022, cooler than average spring maximum temperatures were experienced at Tulloona and Gurley while at Spring Ridge maximum spring temperatures were warmer than average. In contrast, in 2023 maximum winter and spring temperatures were 1.5⁰C higher than monthly averages between June and October (Appendix A). There were large differences in annual and growing season rainfall (May-October, GSR) between 2022 and 2023 (Table 4). In 2022, annual rainfall was 62-241mm above the long term average while in 2023 annual rainfall was 163-195mm below the long-term average. More importantly, were the differences in growing season rainfall. In 2022 growing season rainfall was 202-242mm above average (Decile 10) while in 2023 it was 136-175mm below average (Decile 1). However, high levels of soil water in 2023 compensated for the lack of in-crop rain. Table 4. Plant available water and rainfall data for barley PGR trials in 2022 and 2023 Site Trial Planting PAW (mm) Annual rainfall (mm) Annual rainfall (mm) Growing season rainfall (mm)* Growing season rainfall (mm)*       Year of trial Long Term Average Year of trial Long Term Average Tulloona PGR over commercial crop 165 754 548 456 214 Gurley PGR x Variety 165 622 560 406 204 Spring Ridge PGR x Variety 202 870 629 465 254 Boomi PGR x Variety x 2 Times of Sowing 201 367 543 50 201 Gurley PGR x Variety x 2 Times of Sowing 198 365 560 68 204 Breeza PGR x Variety 253 484 647 122 265 Pallamallawa# PGR x Nitrogen 171 459 641 58 233 *Measured as rainfall from May to October, #Trial failed due to residual herbicide damage Plant height was measured during early grain fill in each replicate from ground level to the top of the spike excluding awns of the main tiller. Lodging was scored visually with a 0 for no lodging and 10 for 100% of the crop completely lodged and flat against the ground. In 2023 no lodging was evident at Boomi, Gurley or Pallamallawa thus scores were not recorded. Biomass cuts were taken at GS 30, GS 55 and GS 99 at 30mm above ground level with 1 x 0.5m quadrat.