Functionally diverse flax-based rotations improve wild oat (Avena fatua) and cleavers (Galium spurium) management

Abstract

Wild oat (Avena fatua L.) and false cleavers (Galium spurium) are currently a challenge to manage in less competitive crops such as flax (Linum usitatissimum L.). Increasing the functional diversity in crop rotations can be an option to improve weed management. Nonetheless, this strategy is not tested in flax in Western Canada. A 5-yr (2015-2019) crop rotation study was carried at three locations in western Canada to determine the effect of diverse flax-based crop rotations with differences in crop species, crop life cycles, harvesting time and reduced herbicides on managing A. fatua and G. spurium. The perennial rotation (flax-alfalfa (Medicago sativa L.)-alfalfa-alfalfa-flax) under reduced herbicide use was found to be the most consistent cropping system, providing similar A. fatua and G. spurium control to the conventional annual flax crop rotation[flax-barley (Hordium vulgare L.)-flax-oat (Avena sativa L.)-flax] with standard herbicides. At Carman, this alfalfa rotation provided even better weed control (80% A. fatua, 75% G. spurium) than the conventional rotation. Furthermore, a greater A. fatua control was identified compared to conventional rotation where two consecutive winter cereal crops were grown successfully in rotation (flax-barley-winter triticale (x Triticosecale ex A. Camus)-winter wheat (Triticum aestivum L.)-flax), greater A. fatua control was observed compared to the conventional crop rotation under standard herbicides. Incorporation of silage oat crops did not show consistent management benefits compared to the perennial alfalfa rotation but were generally similar to the conventional rotation with standard herbicides. The results showed that perennial alfalfa in the rotation minimized G. spurium and A. fatua in flax cropping systems, followed by rotations with two consecutive winter cereal crops.

Using integrated weed management systems to manage herbicide-resistant weeds in the Canadian Prairies

“…In this study, diversifying rotations to spring annuals or including a winter cereal was not enough to forego incrop herbicides while maintaining or reducing wild oat seed densities. This result agrees with recent results from Benaragama et al (2022), where crop diversification strategies in which spring annual crops were included in rotation did not improve management of wild oat.…”

“…Interestingly, the wild oat seed-bank densities were only maintained at the same level as the standard in the treatments where there was 1 year of silage barley, compared with 2 years of silage barley (treatments 13 and 14 vs. treatments 11 and 12; Figure 9). This is consistent with Benaragama et al (2022) where, in a flax-based rotation where a single year of silage barley was employed, there was no obvious benefit when compared with that in the spring annual grain crop. The alfalfa treatment also provided 3 years of no grass herbicides while maintaining the wild oat seed bank, even reducing the seed bank at two of the five locations.…”

“…This is an area that requires further investigation. Benaragama et al (2022) noted benefits from winter cereals when two consecutive winter crops were incorporated into a rotation, a cropping system rotation that was not included in the current study. However, this only occurred at locations with good winter crop establishment (Benaragama et al, 2022) as successful establishment and overwinter survival of winter-annual crops were required for competition with weeds, similar to the observations in this study.…”

“…Benaragama et al (2022) noted benefits from winter cereals when two consecutive winter crops were incorporated into a rotation, a cropping system rotation that was not included in the current study. However, this only occurred at locations with good winter crop establishment (Benaragama et al, 2022) as successful establishment and overwinter survival of winter-annual crops were required for competition with weeds, similar to the observations in this study. Perennial alfalfa has been shown to successfully manage cleavers (Benaragama et al, 2022); however, this benefit was not apparent in the current study for seedling densities although seed-bank densities were reduced in Lacombe.…”

“…Available HWSC methods include chaff collection, impact mills, narrow windrow burning, chaff lining or tramlining, and bale-direct systems (Walsh et al, 2018) Many of the IWM cropping system studies in Western Canada have focused on management of wild oat (Harker et al, 2003;Harker et al, 2009;O'Donovan et al, 2013;Harker et al, 2016). A recent study found that rotations that included a perennial crop, or with two winter cereal crops in rotation or with incorporation of silage crops in a flax (Linum usitatissimum L.) rotation, were successful in managing wild oat and false cleavers (Galium spurium L.) with reduced herbicide applications (Benaragama et al, 2022). Although true IWM strategies can increase costs and complexity of managing weeds (Norsworthy et al, 2012;Ervin and Frisvold, 2016;Owen, 2016), these strategies are needed to provide growers options and strategies to reduce their reliance on herbicides, particularly in the face of continuously increasing herbicide-resistance pressures (Heap, 2023).…”