Imtrader Ed. 13 – Summer Herbicide effects in Winter

The aim of this research is to investigate the plant-back window for a number of summer fallow herbicide options when applied under lower rainfall conditions in sandy, acidic soils.

Key points

  • Little robust information available on the effect of summer fallow herbicides for plant-backs to winter cereals grown in the lower rainfall zones and sandy, acidic soils
  • Changing weed profiles over summer leading to interest in some alternate chemistries
  • Some summer fallow chemistries appear to significantly reduce crop biomass.

 

Trial Layout
The trial is to be conducted in accordance with the principles of ANOVA, incorporating a Randomised Complete Block Design (RCBD) with 12 treatments and 3 replications, totalling 36 plots.

Plot size is 10 meters long by 2 meters wide.

There are four application timings with the same treatment list and randomisation, with the earliest timing (121 DBS) the most northerly block (closest to entryway). Applications were made as per the below.


The trial site was kept free of weeds (Button grass,
Tarvine) by regular application of Glyphosate only. The reason for keeping the site weed free was to prevent any effects of treatment efficacy on weeds creating uncontrolled variation in the site via weed effects (moisture removal, allelopathy etc) which have the potential to mask direct plantback issues.DBS = Days before sowing

Results/comments
Figure 1; Cumulative and daily rainfall for the trial site from trial commencement to 30 June 2018

 

Table 1; Comparison of treatment means. Mean number of germinated wheat cv. Havoc seedlings

Table 2; Comparison of treatment means. Mean Biomass percentage of wheat cv. Havoc treated 121 Days Before Sowing

Table 3; Comparison of treatment means. Mean Biomass percentage of wheat cv. Havoc treated 86 Days Before Sowing

Table 4; Comparison of treatment means. Mean Biomass percentage of wheat cv. Havoc treated 57 Days Before Sowing

Table 5; Comparison of treatment means. Mean Biomass percentage of wheat cv. Havoc treated 0 Days Before Sowing

The rainfall for the site over the summer post application of the treatments was not high, with roughly 25mm received post application of 121 DAB and 86 DBS treatments and 15mm for the 57 DBS treatment. This amount of rainfall is generally considered inadequate to break down/dissipate most problematic actives. The rainfall for the site over the summer post application of the treatments was not high, with roughly 25mm received post application of 121 DAB and 86 DBS treatments and 15mm for the 57 DBS treatment. This amount of rainfall is generally considered inadequate to break down/dissipate most problematic actives.

When applied well in advance of seeding (121 – 86 DBS), none of the treatments appear to have affected the germination of wheat. However the application of Haloxyfop at timings closer to seeding (57 – 0 DBS) have significantly reduced the germination of wheat compared to the untreated control.

When assessed by visual biomass percentage, a number of treatments have affected the vigour of wheat. Interestingly, most treatments did not show any effect on biomass until 54 days post sowing, which when applied to a whole paddock situation may lead to mis-diagnosis of the cause of the thin crop/poorly performing crop. Some of the biomass reductions may not even be noticeable at all in a large scale situation without untreated areas for comparison. In short, the biomass results indicate;
– Haloxyfop caused significant biomass reduction when applied 57 days before seeding or directly in front of the seeder bar.
– Metsulfuron (Ally) caused significant biomass reductions when applied out to 86 days before seeding.
– Frenzy (Monza) caused significant biomass reductions when applied up to 57 days before seeding

On the positive side, most of the group Is do not appear to have caused any issues to-date, although this result needs to be viewed with caution as it is from one year of data and does not yet account for effects to final yield.

Acknowledgments: Thanks to the McCreary’s for seeding and assisting with site maintenance.
Contact
Michael Macpherson
michael.macpherson@imtrade.com.au
0427746029

 

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