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Australian Herbicide Resistance Initiative (AHRI)

Never mix trifluralin and…

Triple disc of machine for agriculture

Mum – ‘blue and green should never be seen’

Wife – ‘never mix swirls and stripes’

Dad – ‘never drink on an empty stomach’

Sam Kleemann – ‘never mix trifluralin and a single disc seeder’.

It will come as no surprise to many that researcher Sam Kleemann from the University of Adelaide found that trifluralin gave poor ryegrass control and reduced crop establishment when wheat was sown with a single disc opener in three trials between 2008 and 2012. Some growers favour single disc, zero till seeding because the lack of soil disturbance may reduce weed emergence. Sam observed this phenomenon in one trial, however the low ryegrass number in the zero till plots went on to produce a lot of seed due to low competition from the crop.

What is encouraging from this research is that some triple disc seeders do throw enough soil to incorporate trifluralin and give good crop establishment. Sam also found that the new herbicides Boxer Gold® and Sakura® gave good weed control with good crop safety with a range of seeding machinery, although these new herbicides are not currently recommended for use with disc seeders in Australia.

Single disc seeder + trifluralin = poor crop establishment + poor weed control

Single_disc_x_treflan_damage_poor_ARG_control_compressed

Sakura + Single disc seeder = good crop establishment + excellent ryegrass control

Single_disc_x_Sakura_excellent_ARG_control_compressed

This AHRI insight is a summary of research that was conducted by Sam Kleemann, Chris Preston and Gurjeet Gill from the University of Adelaide. The research was published in the Weed Science Society of America journal in April 2014.

We know three things about trifluralin

  1. It must be incorporated into the soil soon after application to avoid losses through volatilisation. A very thin layer of soil is enough to stop volatilization of trifluralin.
  2. It is tightly bound to organic matter so interception by crop residues on the soil surface can reduce its effectiveness.
  3. Mixing trifluralin with wheat seed results in significant reductions in wheat establishment. Ideally a seeding system should provide some separation between crop seed and trifluralin.

There are three rules that every agronomist lives by. In priority order;

  1. Don’t kill the crop
  2. Kill the pest (weeds, insect, disease)
  3. Achieve 1 and 2 at the lowest possible cost.

In this research, Sam Kleemann found that the combination of trifluralin and single disc seeding broke rules 1 & 2 – crop damage and poor weed control – worst case scenario. At least trifluralin is cheap!

Rule #1 – don’t kill the crop

Crop Establishment

Trifluralin 1.5 L/ha roughly halved the establishment of wheat sown with a single disc opener at each of three trials.

crop_est_1

Boxer Gold® also caused a reduction in wheat establishment sown with a single disc in 2011 and 2012.

crop_est_2

Rule #2 – kill the weeds

Ryegrass control

The 2012 trial gave the best comparison in ryegrass control between seeding systems and herbicides.

Triple disc of machine for agriculture
K-Hart triple disc

JD_single_disc
John Deere JD90 single disc

Let’s break down the results

1. More soil disturbance = more ryegrass germinates – The triple disc machine stimulated a bigger ryegrass germination than the single disc machine in the absence of herbicide due to the level of soil disturbance

ryegrass_germ_no_herb

2. Only 10% ryegrass control with trifluralin when sown with a single disc compared to 80% control when wheat was sown with triple disc. The single disc machine did not give enough soil disturbance to cover the trifluralin with soil resulting in trifluralin volatilizing and reducing the effective rate of trifluralin.

ryegrass_germ_trifluralin

3. Excellent (70-86%) ryegrass control with Boxer Gold® or Sakura® regardless of seeding machine. The combination of Sakura® with single disc seeding achieved the highest level of ryegrass control in the trial. Perhaps the low soil disturbance with the single disc reducing the stimulation of ryegrass emergence, combined with the non-volatile herbicide Sakura® was the key to success.

ryegrass_germ_boxer_sakura

4. The lowest wheat yield was achieved with trifluralin and single disc seeder. Trifluralin reduced wheat establishment by 59% which reduced the crop’s ability to compete with weeds. Conversely, the highest yield was achieved for the treatment with the lowest ryegrass density and best crop safety – single disc opener plus Sakura®

Table 1. Wheat yield (kg/ha) for triple disc versus single disc seeding for a range of pre-emergent herbicide treatments at Roseworthy, SA in 2012.

table_1_wheat_yield_

Crop competition

Wheat plant vigour for single disc seeding systems was observed to be low compared to other seeding systems. This allowed the ryegrass to tiller well in this low crop competition environment. The low soil disturbance of the single disc seeding system may appear to be beneficial given the low numbers of ryegrass that germinated in these plots, however, these ryegrass were able to set a lot of seed due to a lack of competition from the crop.

ryegrass_germ_and_tillers_

Summary

Many grain growers have steered away from disc seeding machines because they would like to use trifluralin for ryegrass control. This research shows that this is true for single disc openers, however, there are other disc machines that are now capable of achieving good ryegrass control with trifluralin with good crop safety.

Trial Details

This research was conducted on sandy loam soil over calcareous clay at Roseworthy in the lower North region of South Australia. Wheat was sown into Faba bean or lentil stubble. Annual rainfall ranged from 307mm to 419mm in the years of the trials.

In this research the single disc seeder (Austil in 2008 and JD90 in 2011 & 2012) was compared to a K-Hart triple disc seeder and a Primary Sales knife point and presswheel seeder (2008 & 2011). The herbicides trifluralin 480 1.5L/ha, Boxer Gold® 2.5L/ha (Prosulfocarb + S-metolachlor) and Sakura® 118g/ha (Pyroxasulfone) were applied immediately pre-sowing of the various seeding machines.

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