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.

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

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