Current and future site-specific weed control options

Take home messages

  • “Weed Chipper” is a targeted tillage system developed for site-specific fallow weed control based on a rapid response tyne
  • Site specific weed control (SSWC) creates the opportunity to use alternative physical weed control technologies.

Background

The reliance on herbicidal weed control in northern region fallows has led to widespread herbicide resistance evolution in major weed species. As glyphosate is the most widely used herbicide for fallow weed control resistance to this herbicide is increasing at an alarming rate. There is also increasing frequency of resistance to selective herbicides that are being introduced to try and manage glyphosate resistant populations. Alternate non-chemical weed control techniques are desperately needed that are suited to routine use in northern region cropping systems.

Physical and thermal weed control techniques were in use well before herbicides were introduced and the development of new options has continued throughout the herbicide era. However, most of these technologies have not been adopted, primarily due to cost, speed of operation and fit with new farming systems. The introduction of weed detection and actuation technologies creates the opportunity to target individual weeds i.e. site-specific weed control (SSWC). This greatly increases the potential cost-effectiveness of many directional physical weed control techniques in conservation cropping systems.

Aims

  1. To develop a rapid response tyne based on a hydraulic break-out tyne
  2. Use energy required for effective weed control to compare the efficiency of alternate weed control techniques

Method

Development of a rapid response tyne

A rapid response tyne system has been developed with the operational specifications of being able to specifically cultivate targeted weeds when present in a field at densities of up to 1.0 plant/10 m2 at an operation speed of 10 km/h. To permit timely development, the rapid response tyne concept was based on the retrofit of a Shearer Trashworker tyne with a hydraulic breakout system. The Shearer Trashworker was chosen due to its robust build, reputation and prevalence across Australian cropping systems. Its hydraulic breakout system is typical of many other manufacturers thus permitting a design approach which could be adapted to accommodate other arrangements. Although hydraulic systems are not traditionally used in such dynamic environments, to aid timely adoption and acceptance by farmers it seemed sensible to not deviate too far from current accepted and widely adopted agricultural principles.

Whilst focusing on the development of the rapid response tyne around a conventional cultivator, achieving the outcome efficiently and elegantly was not straightforward. As traditional cultivator bars are designed for continuous tillage and full-time tool-soil interaction, the new application required detailed engineering to modify the hydraulic system, mechanism functionality and optimise performance all whilst being highly constrained by the existing geometry.

The initial proof-of-concept design focussed the engineering on minimising the number of additional components and keeping the design simple whilst achieving the chipping action similar to a conventional hoe in well under half a second. A modular approach to the design was taken so as to permit the system to be scaled readily as confidence in system performance was achieved. The Shenton Park rig provided the initial proof-of-concept and the other rigs were used for weed kill testing (Figure 1A to C).

Weed control efficacy

Field testing using the two prototype rigs at the two northern region locations (QDAF and Narrabri) was conducted on a range of fallow weed species. The targeted tillage system was evaluated in a series of field trials for efficacy on weeds of winter fallows (annual ryegrass, wild oats, sowthistle and wild turnip) and summer fallows (barnyard grass, feathertop Rhodes grass, fleabane and sowthistle). At Narrabri, summer and winter field trials investigated the efficacy of the response tyne on the targeted weeds species established at eight growth stages (Table 1).

As the initial mandate for the project was to develop the mechanical response tyne and not the sensor system, the evaluation experiments used a simple photo detector arrangement to trigger the response tyne. A reflector was aligned next to each plant in the plot trial and together with the known travel speed, the system was calibrated to trigger the rapid response tyne when the light beam aligned with the reflector and hence with the weed.

Comparison of weed control technologies

The direct energy requirements for the control of two-leaf weed seedlings were estimated from published reports on the weed control efficacy of a comprehensive range of physical weed control techniques (Table 3). To determine the energy requirement per unit area, a weed density of 5.0 plants/m2 was chosen to represent a typical weed density in Australian grain fields, based on results from a recent survey of Australian grain growers (Llewellyn et al. 2016).

Results

Development of a rapid response tyne

Significant engineering research, development and testing were conducted predominantly around the Shenton Park test rig at UWA (Figure 1A). As with any engineering design, the process involved iterative improvements to the design layout. Once the system was able to achieve a chipping cycle time of less than 400 ms from actuation to return to standby position and the design had been simplified and deemed reliable, the pre-commercial rig was designed and built. Detailed explanation of the engineering process and results will be presented in forthcoming publications.

This shows photos of initial proof-of-concept rig (Shenton Park) (A), Narrabri trailer mounted self-powered rig (B) and QDAF 3-point-linkage rig (C) and Pre-commercial rig – the ‘Weed Chipper’ (D) used in the testing and validation of targeted tillage fallow weed control. Figure 1. Initial proof-of-concept rig (Shenton Park) (A), Narrabri trailer mounted self-powered rig (B) and QDAF 3-point-linkage rig (C) and Pre-commercial rig – the ‘Weed Chipper’ (D) used in the testing and validation of targeted tillage fallow weed control.

Weed kill field testing demonstrated very high efficacy on all targeted summer and winter annual weeds regardless of growth stage (Tables 1 and 2). The survival of any weeds during testing was due to cultivator sweeps not being suitable for targeted tillage. Weed control was 100% effective when the weed was targeted by the point of the sweep, however there was high weed survival when the weed was hit by sweep side. There was also reduced efficacy when weeds were excessively large. When feathertop Rhodes grass was >50cm diameter there was only poor control (Table 2). The system is highly effective on both broadleaf and grass weeds with potentially little resulting soil disturbance (Figure 2).

Table 1. Response tyne efficacy following direct or partial sweep impact on four winter and three summer weed species at eight growth stages, Narrabri NSW 2017 and 2018

Planting date

Wild oats
(% control)

Turnip weed
(% control)

Sowthistle
(% control)

Annual ryegrass
(% control)

Feathertop Rhodes grass

Barnyard grass

Fleabane

Direct contact

Partial contact

Direct contact

Partial contact

Direct contact

Partial contact

Direct contact

Partial contact

Direct contact

Partial contact

Direct contact

Partial contact

Direct contact

Partial contact

2 leaf

100

0

100

100

100

 

100

0

100

-

100

-

100

-

4 leaf

100

-

100

0

100

-

100

0

100

-

100

-

100

-

6 leaf

100

-

100

100

100

-

100

0

100

-

100

-

100

-

8 leaf

100

0

100

-

100

 

100

0

100

-

100

-

100

-

10 leaf

100

0

100

-

100

-

100

0

100

-

100

-

100

-

Bolting/tillering

100

0

100

-

100

-

100

0

100

-

100

-

100

-

Early flowering/heading

100

0

100

-

100

 

100

0

100

-

100

-

100

-

Flowering

100

-

100

-

100

-

100

0

100

-

100

-

100

0

- indicates no treatments where there was partial contact of the tyne with the weed.

These photos show wild oats pre- targeted tillage (A), post-targeted tillage (B) and the resulting “divot” (C) Figure 2. Wild oats pre- targeted tillage (A), post-targeted tillage (B) and the resulting “divot” (C)

Table 2. Weed control efficacy of the rapid response tyne on four weed species at three growth stages combined results from Warwick and Gatton 2018

Weed species

Growth stage

Control (%)

Barnyard grass

Small (<30cm)

100a

 

Medium (30-50cm)

97.8ab

 

Large (>50cm)

95.6ab

Feathertop Rhodes grass

Small (<30cm)

97.4ab

 

Medium (30-50cm)

92ab

 

Large (>50cm)

86.1bc

Wild oats

Small (<30cm)

99.1a

 

Medium (30-50cm)

98.7a

 

Large (>50cm)

98.1ab

Sowthistle

Small (<30cm)

89.9b

 

Medium (30-50cm)

79.4c

 

Large (>50cm)

73.8c

LSD P=0.05

 

8.2

Inclusion of weed detection technologies

The efficacy of targeted tillage for weed control is entirely reliant on accurate weed detection. Given that the initial use of targeted tillage will be in fallow, then it is appropriate that current available real-time detection technologies be incorporated in preparation for commercial use. Current boom spray mounted detection systems (WeedSeeker® and WEEDit®) are coupled to spray nozzles that can be rapidly triggered. Preliminary tests using the WEEDit sensing system to trigger the hydraulics on the Shenton Park rig demonstrated its high suitability to the fallow application. The WEEDit system was chosen as being more suitable system for targeted tillage and has now been incorporated into the pre-commercial Weed Chipper rig. Trials using the system coupled with the 6m pre-commercial Weed Chipper, Figure 1D, are currently underway.

There are a group of thermal weed control technologies (flaming, hot water foaming, steaming, etc.) using chemical or electrical energy that may be used for broadcast weed control (Table 3). In comparison to tillage and herbicide-based options, these approaches are considerably more energy expensive. With 100 to 1000-fold higher energy requirements, it is not surprising that these technologies have not been widely adopted for use in large scale cropping systems, although in more intensive operations, flaming is used to some extent.

Table 3. Total energy requirement estimates for alternative weed control options applied as broadcast treatments. Estimates are based on the control of two-leaf weeds present  at five plants/m2.

Weed control method

Energy consumption
(MJ/ha)

Flex tine harrow

4

Sweep cultivator

11

Rotary hoe

13

Organic mulching

16

Rod weeding

18

Spring tooth harrow

22

Basket weeder

29

Roller harrow

29

Disc mower

31

Tandem disk harrow

36

Flail mower

57

Offset disk harrow

64

UV

1701

Flaming

3002

Infrared

3002

Hot water

5519

Hot foam

8339

Steam

8734

Freezing

9020

Hot air

16902

Microwaves

42001

Plastic mulching

211003

Site-specific weed control (SSWC)

The opportunity for substantial cost savings and the introduction of novel tactics are driving the future of weed control towards SSWC. This approach is made possible by the accurate identification of weeds in cropping systems using machine vision typically incorporating artificial intelligence. Once identified, these weeds can be controlled through the strategic application of weed control treatments. This precision approach to weed control creates the potential for substantial cost savings (up to 90%) and the reduction in environmental and off-target impacts (Keller et al. 2014). More importantly for weed control sustainability, SSWC creates the opportunity to use alternative physical weed control options that currently are not suited for whole paddock use.

Accurate weed detection allows physical weed control treatments to be applied specifically to the targeted weed. As weed identification processes develop to include weed species, size and growth stage, there exists the potential for some approaches (such as electrical weeding, microwaving and lasers) to be applied at a prescribed lethal dose. This dramatically reduces the amount of energy required for effective weed control (Table 3). For example, microwaving, as one of the most energy expensive weed control treatments as a broadcast treatment (42,001 MJ/ha), requires substantially less energy when applied directly to the weed targets (17.8 MJ/ha). Therefore, even though the same number of weeds are being controlled (five plants/m2), the specific targeting of these weeds results in a 99% reduction in energy requirements.

The accurate identification of weeds allows the use of alternative weed control technologies that are not practically suited for use as whole paddock treatments. For example, lasers are typically a narrow beam of light focused on a point target. In a SSWC approach with highly accurate weed identification and actuation, lasers can be focused precisely on the growing points of targeted weeds, concentrating thermal damage. By reducing the treated area of the weed, off-target losses are further reduced allowing additional energy savings.

Table 4. Total energy requirement estimates for alternative weed control options when applied as site-specific treatment. Estimates are based on the control of two-leaf weeds present  at five plants/m2.

Weed control method

Energy consumption
(MJ/ha)

Concentrated solar radiation

14.4

Precise cutting

14.4

Pulling

14.4

Electrocution: spark discharge

14.5

Nd:YAG IR laser pyrolysis

15.1

Herbicides

14.8

Hoeing

15.7

Water jet cutting

15.8

Stamping

16.5

Nd:YAG IR laser pyrolysis

16.9

Microwaves

17.8

Abrasive grit

24.5

Thulium laser pyrolysis

25.9

CO2 laser cutting

54.8

Targeted flaming

59.9

Electrocution: continuous contact

60.9

Nd:YAG laser pyrolysis

84.4

CO2 laser pyrolysis

92.3

Nd:YAG UV laser cutting

129.4

Hot foam

131.3

Dioide laser pyrolysis

133.1

Nd:YAG IR laser cutting

204.4

Targeted hot water

517.6

Conclusion

The response tyne’s mechanical nature enables it to control weeds with greater flexibility around environmental conditions such as wind, humidity and heat. Its ability to handle a vast range of plant stages of weeds will likely reduce the number of passes required to manage fallow weeds compared to current herbicide practice and help mitigate the current slower travel speed and narrower coverage. The periodic tilling action required for low-density weed populations will also permit the Weed Chipper to be coupled to low horsepower tractors. With no direct need for chemical use for this system there are likely to be significant cost savings to growers using the Weed Chipper system.

Targeting treatments on individual plants such as in SSWC, results in significant energy savings and makes previously impractical options on a broadcast basis available for use on a site-specific basis. The focus for SSWC research is now dually focussed on the development of weed recognition systems and the evaluation of alternate weed control technologies such as lasers and electrical weeding.

Acknowledgments

The research undertaken as part of this project is made possible by the significant contributions of growers through both trial cooperation and the support of the GRDC, the authors would like to thank them for their continued support. The authors are grateful to Allan Spurling and Karl Teune from David Nowland Hydraulics (Bunbury, Western Australia) for developing the physical hydraulic circuit. The willing advice from Ray Harrington, Geoff Glenn and Mic Fels is also gratefully acknowledged.

Further reading

Site-specific weed control - GRDC Grains Research Update paper, July 2018

References

Llewellyn R., Ronning D., Clarke M., Mayfield A., Walker S., Ouzman J. (2016) Impact of weeds in Australian grain production: the cost of weeds to Australian grain growers and the adoption of weed management and tillage practices. CSIRO, Australia.

Contact details

Michael Walsh
University of Sydney
12656 Newell Highway, Narrabri, NSW 2390
Ph: 02 6799 2201
Mb: 0448 847272
Email: m.j.walsh@sydney.edu.au

Andrew Guzzomi
University of Western Australia
35 Stirling Highway, Crawley, WA 6009
Ph: 08 6488 3883
Mb: 00428396262
Email: Andrew.guzzomi@uwa.edu.au

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GRDC Project code: UWA00171, US00084