Herbicide Efficacy of Spot Spraying Systems in Fallow and Postharvest in the Pacific Northwest Dryland Wheat Production Region.

Nicholas Genna,Jennifer Gourlie,Judit Barroso

doi:10.3390/plants10122725

Abstract

Real-time spot spraying technology has the potential to reduce herbicide costs and slow herbicide resistance. However, few studies exist on the efficacy of this technology in the Pacific Northwest (PNW). This research compared the herbicide efficacy (reduction in weed density and cover) of WEED-IT and WeedSeeker spot spraying systems to uniform spraying in fallow and postharvest in 2019 and 2020. Weed community types included naturally occurring weeds, natural + Russian thistle (Salsola tragus L.), or natural + kochia (Bassia scoparia (L.) A. J. Scott). Herbicides included glyphosate or the pre-mix bromoxynil + pyrasulfotole. Additionally, herbicide efficacy was studied with short stubble (~10 cm), tall stubble (~25 cm), and normal stubble (~20 cm) with chaff and straw removed. In fallow, herbicide efficacy was 1.5 times higher for uniform applications than for WEED-IT or WeedSeeker in 2019 and 2020. Herbicide efficacy was also 1.9 times higher for uniform applications in postharvest in 2019 but no differences were found in 2020. The weed community impacted herbicide efficacy but herbicide efficacy did not differ between residue management treatments. Finally, WEED-IT and WeedSeeker used 53% less herbicide volume in comparison to uniform applications. This research demonstrated that spot spraying technology can be efficacious and economical for growers in the PNW.

Highlights

Accepted: 8 December 2021A no-till wheat-fallow rotation relies on herbicides to control weeds in fallow and postharvest
Density and cover were affected by weed community, with glyphosate providing the greatest reduction in natural plots, and bromoxynil + pyrasulfotole in Russian thistle plots
Weeds at either end of the size spectrum, either small or large, may be an issue for spot sprayers in fallow in the Pacific Northwest (PNW) and higher herbicide rates alone may not overcome issues related to suboptimal weed detection

Summary

Introduction

A no-till wheat-fallow rotation relies on herbicides to control weeds in fallow and postharvest. Herbicides are traditionally applied uniformly across fields regardless of weed cover or density. Timmermann et al [1] demonstrated that weed mapping could reduce herbicide costs by 54% compared to a uniform application, but higher labor costs prohibit manual weed mapping by growers. Real-time spot spraying technology was developed to overcome manual labor requirements by differentiating weeds from soil without the need of a weed map [2,3]. Light activated sensors turn individual spray nozzles on and off when weeds are detected to minimize coverage of weed-free soil and maximize herbicide savings. WEED-IT® (Rometron B.V., Steenderen, The Netherlands) and WeedSeeker®

Methods

Results

Conclusion