Double and triple knock strategies for managing ryegrass

Double and triple knock strategies for managing ryegrass

Take home messages

  • Glyphosate and paraquat resistance in annual ryegrass will make knockdown weed control prior to sowing more difficult.
  • Be aware of plant backs when using Group 14 herbicides in knockdown applications or if using glufosinate as a knockdown herbicide.
  • Glufosinate has potential as the first herbicide in a double knock approach.
  • Dry sowing can offer a different alternative to manage glyphosate and paraquat resistant annual ryegrass, however, an effective pre-emergent strategy needs to be employed.

Resistance to glyphosate and paraquat in ryegrass

Recent weed resistance surveys are indicating an increase in glyphosate resistant annual ryegrass (Table 1). Only two samples with resistance to paraquat were identified in this survey, both from South Australia. However, resistance to paraquat has been detected in an increasing number of annual ryegrass populations sent for testing. Resistance to both paraquat and glyphosate makes control of annual ryegrass prior to sowing much more challenging.

Table 1: Extent of resistance to glyphosate in annual ryegrass collected in a random survey of cropping fields across Australia in 2020/2021. Samples were considered resistant if more than 20% of the individuals survived herbicide treatment.

State

Samples tested

Resistance to glyphosate

Resistance to paraquat

  

(% of samples)

(% of samples)

New South Wales

317

23

0

Victoria

183

22

0

Tasmania

21

0

0

South Australia

279

14

0.7

Western Australia

554

12

0

Total

1354

16

0.1

Double knocks and more

The strategy for managing glyphosate resistance is to use a double knock approach. Typically, this is glyphosate followed by paraquat 1–5 days later. The timing of the paraquat application is very important as application at some times can lead to a reduction in efficacy of paraquat on glyphosate resistant annual ryegrass (Figure 1).

Effect of time between applications for glyphosate followed by paraquat double knock on glyphosate resistant annual ryegrass populations. S is a glyphosate susceptible population. R1 and R2 are two glyphosate resistant populations.

Figure 1. Effect of time between applications for glyphosate followed by paraquat double knock on glyphosate resistant annual ryegrass populations. S is a glyphosate susceptible population. R1 and R2 are two glyphosate resistant populations.

With both glyphosate and paraquat resistance, should we be thinking about a triple knock? It will be very challenging to find time to put three knockdown applications out prior to sowing. In any case, the choice of the third knockdown herbicide could delay sowing due to plant backs.

The newer Group 14 herbicides Terrad’or® and Voraxor® are now being frequently used with knockdown herbicides in an effort to get better weed control. Due to plant backs with the higher rates of Voraxor, it is better to use Voraxor with glyphosate in the first knock or to use Terrad’or with paraquat in the second knock.

Is there a role for glufosinate

A set of trials funded by the South Australian Drought Hub was conducted looking at the potential for glufosinate and mixtures of glufosinate with Group 14 herbicides as a potential alternative to glyphosate for pre-sowing weed control (Table 2). Glufosinate mixtures worked best at sites with smaller weeds. For glufosinate to provide effective control of annual ryegrass, the weeds should have no more than three leaves.

Table 2: Biomass present at 28 days after application of glufosinate and glufosinate mixtures at Wangary, Minnipa and Struan in 2022 and at Struan in 2023. Some use patterns are not registered and are included for experimental purposes. Always read and follow product labels.

Herbicide

Rate (g a.i. ha-1)

Wangary

Minnipa

Struan 2022

Struan 2023

Biomass (g/m2)

Nil

 

163.2 a

106.9 a

62.1 a

107.0 a

Glufosinate

750

12.3 b

27.6 bc

40.4 a

36.5 bc

Glufosinate +

Tiafenacil

750

14

29.9 b

22.3 c

21.4 ab

39.6 bc

Glufosinate +

Saflufenacil +

Trifludimoxazin

750

25

12.5

5.1 b

27.0 bc

22.8 ab

32.6 bc

Glyphosate

+

Carfentrazone-ethyl

810

8

6.7 b

20.8 c

0.0 b

9.4 c

Different letters within columns indicate treatment means that are significantly different.

There are many challenges to getting glufosinate to be effective as a pre-sowing knockdown herbicide. In addition to efficacy issues against large weeds, particularly annual ryegrass and wild radish, there is also the need to wait 14 days to sow. This means that glufosinate may prove better as the first application in a double knock use, with paraquat applied 14 days later.

Dry sowing

An alternative approach to manage glyphosate resistant annual ryegrass when the season conditions are appropriate is to dry sow and use pre-emergent herbicides and crop competition to manage the weeds. However, with dry sowing, it is important to choose the pre-emergent herbicides wisely. For dry sowing, more persistent herbicides are better than using less persistent herbicides, such as Boxer Gold® (Table 3). Including an early post-emergent application of Boxer Gold, Arcade® or Mateno® Complete can provide better control of annual ryegrass and provide insurance against poor control of weeds by pre-emergent herbicides due to seasonal conditions (Table 3).

Table 3: Annual ryegrass control in a dry sown wheat trial at Concordia, SA in 2023. Weed counts were made 49 days after sowing. fb = followed by, early post-emergent herbicide products applied 21 days after sowing.

Herbicide product

Active ingredients

Rate used

Annual ryegrass

(plants/m2)

Nil

  

76.8 a

TriflurX

Trifluralin 480 g L-1

2 L ha-1

24.9 b

Sakura Flow

Pyroxasulfone 480 g L -1

210 mL ha-1

13.2 bc

Boxer Gold

Prosulfocarb 800 g L-1 + S-metolachlor 120 g L-1

2.5 L ha-1

37.6 ab

Luximax

Cinmethylin 750 g L-1

0.5 L ha-1

15.2 bc

Mateno Complete

Pyroxasulfone 100 g L-1 + diflufenican 66 g L-1 + aclonifen 400 g L-1

0.75 L ha-1

24.0 b

Mateno Complete

Pyroxasulfone 100 g L-1 + diflufenican 66 g L-1 + aclonifen 400 g L-1

1.0 L ha-1

15.2 bc

Overwatch

Bixlozone 400 g L-1

1.25 L ha-1

14.2 bc

TriflurX

fb Mateno Complete

Trifluralin 480 g L-1

Pyroxasulfone 100 g L-1 + diflufenican 66 g L-1 + aclonifen 400 g L-1

2 L ha-1

0.75 L ha-1

14.7 bc

TriflurX

fb Mateno Complete

Trifluralin 480 g L-1

Pyroxasulfone 100 g L-1 + diflufenican 66 g L-1 + aclonifen 400 g L-1

2 L ha-1

1 L ha-1

6.8 bc

Overwatch

fb Mateno Complete

Bixlozone 400 g L-1

Pyroxasulfone 100 g L-1 + diflufenican 66 g L-1 + aclonifen 400 g L-1

1.25 L ha-1

1 L ha-1

0.5 c

TriflurX

fb Boxer Gold

Trifluralin 480 g L-1

Prosulfocarb 800 g L-1 + S-metolachlor 120 g L-1

2 L ha-1

3 L ha-1

8.3 bc

Different letters indicate treatment means that are significantly different.

Acknowledgements

Some of the information in this report was from a project Cropping Without Glyphosate funded by the SA Drought Resilience Adoption and Innovation Hub as an Innovation project funded by the Commonwealth Department of Agriculture, Fisheries and Forestry. The authors thank project partners Hart Fieldsite Group, Mackillop Farm Management Group, AIR EP and Elders for conducting the trials in that project.

Contact details

Chris Preston
School of Agriculture, Food and Wine
University of Adelaide
0488 404 120
christopher.preston@adelaide.edu.au

GRDC Project Code: UCS2008-001RTX, UOA2007-007RTX,