| Researcher(s) |
Linda Bailey |
|---|---|
| Year(s) | 2021 |
| Contributor | Northern Grower Alliance |
| Trial location(s) |
St Ruth, QLD
|
To evaluate the impact of split application of residual herbicides for grass control pre-plant and in-crop
Key Point: Immediately prior to planting, the grower applied a commercial knockdown treatment to control a low population of emerged weeds. Dual Gold at 500 mL/ha was included in this mixture and was inadvertently applied across the trial area. Consequently, all treatments listed in the result tables had an additional Dual Gold 500 mL/ha applied at sorghum planting. Interpretations and conclusions are more challenging for this trial as the ‘untreated’ reference actually has Dual Gold 500 mL/ha at planting. However, the key messages are still clear and important.
This was a complex trial to evaluate the impact of split or sequential residual herbicide applications for feathertop Rhodes grass (FTR) management both prior to and in sorghum. Dual Gold, Gesaprim or Valor were applied at the end of July or end of August. These treatments either remained as stand-alone or were topped-up with Dual Gold at 1 L/ha, at sorghum planting or early in-crop. Reference treatments were an ‘untreated’ and Dual Gold rates applied at planting or in-crop.
The trial site was compromised when the grower inadvertently applied Dual Gold at 500 mL/ha shortly before commercial planting as a mixture with glyphosate. Consequently, all treatments in the trial (including the ‘untreated’) had an extra 500 mL/ha of Dual Gold at planting. The originally planned ‘top up’ rates of Dual Gold were all reduced by 500 mL/ha.
Levels of rainfall of only ~3-12 mm occurred in the week following each application timing with August and September very dry with <10 mm of monthly rainfall.
At the end of October, MR Taurus sorghum was sown in 90 cm rows into 2020 wheat stubble (~30% ground cover). All treatments were crop safe with no impact on emergence counts or any visual crop effect at 22 days after planting (22 DAP).
Emergence counts for FTR were extremely low. Weed counts at the 2nd application timing (28 DAA) and prior to planting in late October (90 DAA) both showed <0.01 FTR/m2. This was very surprising as there was ~60 mm of rainfall recorded ~2 weeks prior to planting. FTR assessment at 22 DAP still showed negligible levels of FTR but this was more expected as all treatments (including the ‘untreated’) had received at least 500 mL/ha of Dual Gold at planting. Plots were still clean when the in-crop application was conducted.
A final weed assessment was conducted in early February during sorghum grain fill. FTR counts were still very low despite >340 mm of rain after planting. The factorial analysis however clearly showed that fallow treatments of Dual Gold or Valor provided significantly improved FTR control compared to Gesaprim. There were no significant differences between application timings or ‘top-up’ rates. There were also clear differences in broadleaf weed efficacy apparent at this assessment. Valor provided effective and significantly improved control of flaxleaf fleabane and common sowthistle compared to either Dual Gold or Gesaprim. In addition, Gesaprim provided improved suppression of flaxleaf fleabane compared to Dual Gold but not at a commercially useful level. There were no significant differences evident between application timing or the ‘top-up’ treatments.
Despite the trial being located in a paddock with a history of FTR issues, emergence of the target weed was very low. The only sound conclusion from this trial is that Gesaprim was inferior to both Dual Gold and Valor for FTR activity. No evaluation could be made on the impact of application timing or the sequential treatment strategies for FTR management. In addition, Valor provided extended and high levels of control of both flaxleaf fleabane and common sowthistle.
| Lead research organisation |
Northern Grower Alliance |
|---|---|
| Host research organisation | N/A |
| Trial funding source | GRDC NGA2009-002RTX |
| Related program | N/A |
| Acknowledgments | N/A |
| Other trial partners | Not specified |
| Crop type | Cereal (Grain): Sorghum |
|---|---|
| Treatment type(s) |
|
| Trial type | Experimental |
| Trial design | Replicated |
| Sow date | Not specified |
|---|---|
| Harvest date | Not specified |
| Plot size | Not specified |
| Plot replication | Not specified |
SILO weather estimates sourced from https://www.longpaddock.qld.gov.au/silo/
Jeffrey, S.J., Carter, J.O., Moodie, K.B. and Beswick, A.R. (2001). Using spatial interpolation to construct a comprehensive archive of Australian climate data , Environmental Modelling and Software, Vol 16/4, pp 309-330. DOI: 10.1016/S1364-8152(01)00008-1.
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