Can a shielded sprayer reduce ryegrass?

Take home messages

  • In a high ryegrass situation, a shielded sprayer reduced ryegrass tillers by 43 per cent.
  • Shielded sprayers achieve higher levels of control in low weed populations.
  • Multiple weed management strategies and modes of action are the best defense in a high weed situation.


Herbicide resistance is a growing area of concern in Australian farming systems. Weed management is a complex issue, trying to maintain a balance between resistance, control achieved and expenses. The shielded sprayer is a piece of technology that promises to make weed management simpler, however there is little research evaluating its use.

There are two types of shielded sprayer technology; one that is physically tracked down the row by the standing crop and one that uses a camera to guide the shield apparatus down the row. Both these setups are being used successfully in commercial farm situations and the development of GPS and seeder technology now allows for near perfect inter-row sowing and spray technology.

Despite the technological and agronomic advances in shielded sprayers there has been relatively low adoption due to time, costs and risks in setting up the system. Possible challenges to adoption are:

  • cost of machinery: it is not as simple as just buying a shielded sprayer – you need to invest in the entire system for effective adoption. This includes wide rows (15 inches or more), precise seeding equipment (2cm steering accuracy and possible seeding implement steering if needed to keep from going offline, this allows for perfect straight rows down the paddock)
  • paddock layout: obstacles such as trees in the paddock increase the risk of going offline and nonselective sprays killing the crop
  • time, labour and skills for setting up the system
  • loss of yield in cereal rotation from wide rows
  • loss of yield from herbicide damage
  • possible increase in reliance on herbicides like glyphosate which may lead to an increase in herbicide resistance.

However there are many advantages of using a shielded sprayer system including:

  • lower chemical costs: cheap, effective, non-selective herbicides can be used during a cereal rotation without the need for expensive pre-emergent and selective chemicals
  • doesn’t limit rotations and can avoid getting locked into a group B herbicide rotation
  • advantages of wide rows for pulses in the rotation such as better disease control and better moisture availability
  • excellent weed control which will constantly lower the weed seedbank
  • higher returns, with lower risk of production over time.

Note: Some of the herbicides used in this trial are not registered for use in certain crops, and were tested for experimental purposes only. Always read the label and adhere to directions when using herbicides.


To investigate the agronomic use and economic value of shielded sprayers in the Wimmera and Mallee.

Paddock details

Location: Jil Jil
GSR (Apr-Oct): 214mm
Soil type: Sandy clay loam

Trial details

Crop type: Kord wheat
Treatments: Refer to Table 1
Target plant density: 130 plants/m²
Seeding equipment: Knife points, press wheels, 15 inch row spacing
Sowing date: 6 June 2017
Replicates: Four
Harvest date: November 2017
Trial average yield: 1.2t/ha
Previous crop type: Wheat, stubble harrowed

Trials inputs

Fertiliser: Granulock Supreme Z + Impact® @ 55kg/ha at sowing and 100kg/ha of urea applied at GS13.
Pests and disease were controlled according to best management practice.


A replicated field trial was sown using a complete randomised block design according to the treatments in Table 1. Assessments included weed counts (50x76cm including two crop inter rows), tiller counts at GS70 (crop), yield and grain quality parameters.

The shielded spray was applied using a rigid 12 inch shield set-up. It was applied at a water rate of 180L/ha with DG TEEJET 80015VS nozzles. The water rate was exceptionally high as a balance of speed and accuracy in a plot setting needed to be achieved. A much lower water rate could be used in a broadacre setting with modified shields to track the crop rows.

Table 1. The treatment list including herbicides and rates used in this trial.

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Results and interpretation

The trial site was selected based on its high ryegrass population and to provide a consistent weed population so that treatments would not be easily skewed by variability. However, this had its limitations. Due to exceptionally high ryegrass numbers and rainfall not allowing high efficacy in all of the pre-emergent herbicides used, no treatment provided an adequate level of ryegrass control. Despite this, there were still significant reductions in weed number which while not necessarily economical, can be applied in principle to a farming system.

The weed assessments were carried out in an area that included both crop row and inter-row as this could be converted into an overall level of control for the crop. It should be noted that particular treatments would have targeted certain areas; the IBS herbicides and shielded sprayer would have targeted the inter-row while only the post emergent Boxer Gold spray would have included both weeds in the inter and intra-row.

The selected site had a known ryegrass problem caused by resistance to several products. This included low trifluralin resistance (30 per cent), medium B-Imidazolinone resistance (60 per cent) and high level A-Fops (95 per cent) resistance. Consequently, the products that could be used on the site were limited – group B’s were avoided. It is acknowledged that in this situation it would be unlikely that a grower would plant wheat, however the site was chosen for its weed numbers and the resistance was worked around by using products with no detected resistance.

Sakura and Boxer Gold provided effective control, achieving a reduction of tillers of 62 per cent and 55 per cent respectively and 79 per cent when used in combination (Table 2). The efficacy may have been higher in the individual treatments if followed by more rainfall – there was only 1mm in June following the sowing of the trial and 14mm broken into small rainfall events following the Boxer Gold application. The size of the ryegrass may also have reduced effectiveness of the Boxer Gold application – ryegrass plants ranged from 1–2 leaf so it is possible the larger ones were unaffected.

Table 2. Pre-emergent and in-crop ryegrass control. Per cent reduction shows per cent tiller reduction of the treatment compared to the control.

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The shielded sprayer (paraquat: treatments 5–8) achieved on average, 43 per cent reduction of the present ryegrass tillers (Table 3). This was notable although not remarkable – the high ryegrass cover and width of the shields meant many plants escaped spray between the shield and the crop row. This was escalated by the IBS treatments controlling ryegrass in the interrow but not within the row. A wider shield could reduce this occurring, as long as the sprayer is able to accurately track a line down the row and not put the crop at risk. In a lower ryegrass population, weed control of the shielded sprayer would increase because fewer weeds would be in the crop row where the shields can’t reach.

Due to the irregular nature of a natural weed population the differences between treatments are not clear-cut however, some conclusions can be drawn. Of the shielded sprayer treatments, the most effective at reducing tillers was treatment 8 – the ‘all in’ (Sakura + Boxer Gold + shield) followed by the individual Sakura + shield (Treatment 6) and Boxer Gold + shield (Treatment 7). The high ryegrass numbers remaining in Treatment 5 (trifluralin + shield) made it no different to the control (Treatment 1), suggesting that shield use is unlikely to achieve adequate control when weed numbers are particularly high.

Shielded sprayers will have limited impact in yield increases as the herbicides are applied later in season so weeds are likely to have affected growth before the herbicide application. This will vary with different shield setups as some are safe to use earlier in the season. Despite this, there was some effect; yields were better in treatments with a higher degree of ryegrass control – particularly those where some extra early weed control was added. This reinforces the message that it is important to control weeds every year as a blowout will eventually effect the bottom line.

The glyphosate treatment controlled ryegrass as effectively as treatment 8, however there was some crop damage, 0.14t/ha yield loss compared to the control. This may have been due to a degree of inaccuracy in the GPS system causing spray to drift into the crop row. While effective for weed control, spraying glyphosate in-crop comes at a huge risk, even minor drift could wipe out a large amount of crop.

Table 3. Ryegrass tiller reduction, grain yield and cost of herbicide application of each

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On-farm profitability

The shielded sprayer was able to achieve 43 per cent control in an extremely high ryegrass population. The effectiveness of the shielded sprayer didn’t appear to vary between treatments, however ryegrass numbers would be considered high in a broadacre situation. It is expected that with lower ryegrass numbers and some alterations to the shield setup this could easily reach higher levels of control, particularly as a larger proportion of the ryegrass in this trial was located in the crop row due to IBS treatments.

Due to the trial being late sown and a dry winter and spring, the trial didn’t reach high yields. Despite there being a yield response, there was no direct economic benefit for ryegrass control in the given year. Regardless, the benefit of controlling weeds cannot be overlooked and shields provide another tool in integrated weed management. When paired with more expensive products in a lower weed situation it is an effective way to reduce seed set for the following year. Additionally, it can be used in conjunction with other weed management strategies such as chaff lining and windrow burning. In a high ryegrass situation like the one described it would be best practice to put in a legume or hay to reduce the weed number to one that would respond more effectively to herbicide in the following season.

Depending on the current system, adoption of shielded sprayers involves adopting the entire system which may involve changing row spacing and ensuring that GPS technology is precise enough for inter-row accuracy or that the system is flexible and moves with the crop. Although the uptake of the system can be costly it has potential to increase profitability over time through lower chemical costs as well as achieving high weed control.


This project was funded through the Hugh DT Williamson Foundation.

Thank you to Lincoln Lehmann for his knowledge and assistance which aided in the design of the shielded sprayer system used in this trial.


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