Integrated weed management to control herbicide-resistant weeds

Integrated weed management (IWM) strategies using increased seeding rates, 2 years of early cut silage barley, and a rotation with competitive winter cereals improved control of wild oat and foxtail species (green and yellow). Treatments with IWM also improved control of lamb’s quarters, cleavers, kochia, wild mustard, and redroot pigweed. Harvest weed seed management provided incremental improvement in weed control.

Herbicides remain the foundation of weed control, but additional tools are needed to provide alternative methods of weed control, and to help slow the development of herbicide resistant weeds.

The objective of this study was to investigate integrated weed management (IWM) strategies that had previously shown potential on some weed species to see if IWM can be used to help control the entire weed community. Additionally, the impact of harvest weed seed control (HWSC) was also assessed as an addition to IWM.

Research was conducted at 6 locations from 2016 to 2020 at Beaverlodge, Lacombe and Lethbridge, AB, Scott and Saskatoon, SK and Carman, MB.  Fourteen treatments using IWM strategies such as rotational crop diversity including winter annuals and perennials, increased seeding rates, crop silaging, chaff collection, with or without in-crop herbicides.

Each treatment was initiated in 2016 with all plots seeded to wheat at a seeding rate of 2× of normal, no herbicide or HWSC in 2016. During the next three years, the IWM treatments were applied.

One IWM treatment compared was crop seeding rate. Spring and winter cereals were seeded at 1x and 2x of typical seeding rates, and canola, field pea and faba bean at 1x and 1.5x of typical seeding rates. Alfalfa was seeded at 1x rate.

The standard crop rotation was wheat-canola with herbicides and no HWSC. Various diversified crop rotations included alfalfa, faba bean, pea, winter wheat, winter triticale, barley for grain, and fall rye.

Another IWM treatment in some rotations was early-cut barley silage harvested 1 week after head emergence (Zadoks 65) to control weeds prior to seed shed.

The HWSC strategy used in the trial was chaff collection and removal. This simulated the use of a physical impact mill that is of interest in western Canada, but not available for plot combines.

The cumulative effects of the treatments were measured in the final year of the study in 2020. In this year, wheat was seeded at 2x rate with no herbicides or HWSC. This eliminated the confounding effects of different crop types, and the reduction of weeds due to herbicides or HWSC.

Each year, the treatments are described by the crop grown, the seeding rate of the crop, whether or not herbicides were used, and whether or not harvest weed seed control was incorporated through use of chaff collection.

Treatment list for the 5-year rotational study

Source: Tidemann et al. 2023

Varied impact on weed control

Overall, the data analysis found success in managing some species of weeds, while other weeds were not successfully managed with these IWM strategies. Wild oat weed densities were lower with increased seeding rates, 2 years of early cut silage barley, and a rotation with competitive winter cereals, even when no in-crop herbicides were applied. Similar results were found with foxtail species (green and yellow).

The impact of IWM treatments on broadleaf weeds was more variable. Treatments with IWM had improved weed control of lamb’s quarters, cleavers, kochia, wild mustard, and redroot pigweed. However, IWM did not have an impact on roundleaf mallow, hemp-nettle, henbit and narrowleaf hawksbeard.

Chaff collection was not a replacement for herbicides, but it did result in incremental control of weeds when incorporated into a weed control strategy.

The density of weeds was also an important factor in the success of IWM. Where weed densities were high, IWM was less successful in improving weed control and reducing the weed seedbank. This indicates the importance of implementing IWM sooner than later to help better manage weeds.

A summary of effective and ineffective management strategies on the various weed species considered in the study

SB indicates effectiveness on seed-bank densities in particular. Treatment not significant indicates no significant treatment effect in the analysis. N/A = Not applicable.

Source: Tidemann et al. 2023

Overall, the research showed that IWM strategies can be effective in reducing the reliance on herbicides and improving weed control for some weed species. It also illustrated the need for further research to understand how IWM can fit into farming practices in western Canada, and what specific strategies are best for which species.

Funding for this project was provided by Western Grains Research Foundation, Alberta Barley, Alberta Canola, and Sask Wheat Development Commission

Tidemann BD, Harker KN, Shirtliffe S, Willenborg C, Johnson E, Gulden R, Lupwayi NZ, Turkington TK, Stephens EC, Blackshaw RE, Geddes CM, Kubota H, Semach G, Mulenga A, Gampe C, Michielsen L, Reid P, Sroka E and Zuidhof J (2023) Using integrated weed management systems to manage herbicide-resistant weeds in the Canadian Prairies. Front. Agron. 5:1304741.


Photo by Breanne Tidemann

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