Key messages

• New weed control technologies under development for US cropping systems
• Widespread occurrence of herbicide resistance in US cropping systems is driving the development of alternative weed control techniques.
• Opportunity to evaluate the potential for these systems in Australian grain production systems

Introduction

Globally the current rate of research and development on weed control technologies for large scale cropping systems is the greatest that we have ever seen. These efforts are being driven by necessity as well as innovation. Worldwide, herbicide availability continues to decline with reduced discovery programs and a focus on breeding efforts. Technological developments in machine learning have created the potential for accurate in-crop weed detection and recognition. To a lesser extent there has also been progress on alternative non-chemical weed control techniques. Although these innovative activities are occurring overseas, mostly in the US as well as Europe, some of the technologies under development would be highly suited for use by Australian grain growers. The more exciting of these developments are summarised here.

Weed Seed Destroyer and WeedErase

Global Neighbor is a start-up based in Ohio who have develop a weed and weed seed control approach based on the combination of 440 nm wavelength blue light and mid-wave infra-red (MWIR) wavelengths heating. The blue light at high intensity is 30 times sunlight, which damages photosynthetic systems (chloroplasts) as evidenced by blackened leaves. MWIR is not present in sunlight and does penetrate the soil to damage weed roots. This technology is currently only commercially available as the handheld WeedErase® system for home garden use.

Further research has found that the combination of high intensity blue light and MWIR can be effective at killing weed seeds. Global Neighbor is now pursuing the use of this approach for targeting weed seeds during harvest. Preliminary studies have shown that complete control of weed seeds in chaff can be achieved within a few seconds exposure. Global Neighbor is pursuing this opportunity with a development labelled the Weed Seed Destroyer (WSD). This technology is still very much under development with prototype systems being produced for benchtop and field testing.

Preliminary testing with a benchtop system at The University of Western Australia has identified high efficacy (>90%) of the WSD on annual ryegrass seed present in wheat chaff. Although initial results are encouraging, extensive benchtop and field testing are needed to establish efficacy of this approach across a range of weed species and crop chaff combinations in varying harvest conditions.

Electrical weeding

There are now commercially available electrical weeding systems suited to largescale crop production systems. Companies including Swiss-based Zasso, UK-based Rootwave and US-based WeedZapper have all developed high voltage electrical weeding systems. In the US the system is being used to target weeds in organic crops where selectivity is based on height differences between crops and weeds. Weeds taller than the crop can be effectively targeted by the high voltage (i.e. >10,000V) electrical weeding systems (Schreier et al 2022).

Australian company Azaneo is pursuing a more novel and precise approach to electrical weeding. Preliminary studies with their low-powered, pulsed electrical weeding system have demonstrated high efficacy at very low power output (<3.0W) on broadleaf and grass weed seedlings in pot and field studies. This technology is being progressed to achieve in-crop control through selective targeting of weed plants.

Weed recognition technologies

The opportunity to specifically target weeds with control treatments is driving considerable research activities and commercial developments. There is a substantial USDA-funded effort on the development of an opensource database of annotated and classified images of major cropping weeds. The researchers have focussed efforts on the major weeds of corn and soybeans, Palmer amaranth and waterhemp. Weed image data is being collected from both in-field and pot-grown scenarios enabling the combined use of real world and synthetic data for training dataset development. The general goal of this research is to provide high-quality image data for the entire weed control industry. The image data is being used to refine software development of weed growing point detection to enable accurate plant recognition despite high occlusion levels (e.g. 50%). Hardware-based research includes evaluation of 3D camera systems for the collection of whole-of-plant data.

Evaluation of gametocides to prevent weed seed production

Gametocides are frequently used to control crossing in the hybrid seed production industry. Through prevention of processes such as anther and pollen development, pollen release etc. gametocides act to prevent pollination from treated plants. A range of chemicals, including some herbicides are routinely used as gametocides in hybrid seed production. Several of these chemicals are now being considered for use in preventing the seed production in weed species of US cropping systems. Targeting the pollen production of herbicide resistant plants could be important in preventing the seed production of these plants and the spread of resistance genes to susceptible populations.

Allelopathic weed control and biological nitrification inhibition

The role of crop-produced chemical growth inhibitors (allelochemicals) on weeds as a component of weed interference (competition + allelopathy) has been documented for many crop:weed combinations (Dayanet al 2010; Konget al 2011). There has been a considerable research effort aimed at understanding the weed control potential of crop root exudates on weeds produced by crop plants (Duke, 2015). Recent research has identified that allelochemicals produced by some crops, largely gramineous species, can also inhibit biological nitrification leading to the more efficient use of soil available nitrogen. Root exudates of these crops have been shown to inhibit nitrification, the conversion of nitrite to nitrate, which contributes to nitrogen loses through NO3- leaching and N2O emissions. The production of secondary metabolites in crop root exudates have the potential to negatively impact weed growth as well as reduce soil nitrogen losses.

Summary

There are several exciting new areas of weed research currently being progressed in the US that would be of value for use in Australian cropping systems. To ensure that Australian growers have access to these technologies there is a need to pursue the specific development of these technologies for use in Australian cropping systems.

Acknowledgements

The author would like to thank the Australian-American Fulbright commission for the opportunity and support to undertake a six-month scholarship. I would also like to thank the host institutions, Kansas State University and Texas A&M for their support during the three months that I spent at each institution.

References

Dayan FE, Rimando AM, Pan Z, Baerson SR, Gimsing AL, Duke SO (2010) Sorgoleone. Phytochemistry 71:1032-1039

Duke SO (2015) Proving Allelopathy in Crop–Weed Interactions. Weed Science 63:121-132

Kong CH, Chen XH, Hu F, Zhang SZ (2011) Breeding of commercially acceptable allelopathic rice cultivars in China. Pest Management Science 67:1100-1106

Schreier H, Bish M, Bradley KW (2022) The impact of electrocution treatments on weed control and weed seed viability in soybean. Weed Technology 36:481-489

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