While herbicides are still effective ongoing research has tried to identify tactics and systems which can be used to manage problem weeds.  This project builds on previous research conducted by Neil Harker who looked at integrated weed management tactics for wild oat.  This project investigated similar tactics, added chaff collection as a harvest weed seed control option, and branched out from wild oat to wild oat, wild buckwheat, and locally important broadleaf weeds at each location.

Treatments included combinations of increasingly diverse crop rotations (canola-wheat, fababeans-barley-canola, peas-winter wheat-canola, silage barley-winter triticale-silage barley, silage barley-fall rye-canola, alfalfa-alfalfa-alfalfa), with various combinations of with and without herbicides, typical or increased seeding rates, and with and without chaff collection. As a five-year study the first year was seeded into a 2x seeding rate of wheat with 0 herbicides applied, and weeds were seeded to allow populations to establish.  The middle three years were where the above crop rotations were implemented, followed by a final year to compare weed populations all in the same crop, in this case a 2x seeding rate of wheat, with 0 herbicides.

Wild buckwheat populations were not significantly affected by any of the crop rotations or integrated weed management techniques tested.  This is an important difference compared to wild oat results shown previously as well as discussed below from this study.  It is likely that the twining/climbing nature of buckwheat allows it to be less affected by the IWM strategies used in this study, which rely heavily on increased competitiveness to affect weed populations.  It will be very important for species such as buckwheat and cleavers to determine which IWM techniques are effective, but also to develop new techniques with better efficacy. These findings carried through to the seedbank analysis where treatments showed limited impacts on the densities of cleavers and wild buckwheat in the soil seedbank. Wild oat results were not as promising as shown in Dr. Harker’s previous IWM research on wild oat.  While early cut barley silage, winter cereals, perennials, and increased seeding rates all were shown to have positive impacts on wild oat management, the wild oat densities at most locations would be unacceptable in a commercial field.  One possible source of variation between the studies is the initial wild oat population when IWM strategies are implemented.  It’s possible that IWM strategies are less effective on high density weed populations. This is an area that requires more research in the future. However, it’s important to note that wild oat populations were still maintained at equivalent level to that observed in the canola-wheat, baseline seeding rate, full herbicide treatment when herbicides were removed in some treatments for 3 years. Adding chaff collection to a full herbicide regime provided incremental weed management benefits, resulting in increased yield across sites. However, the addition of this strategy alone did not allow elimination of herbicide application in the various cropping rotations. It became clear in weed biomasses that the grass weeds, and in particular wild oat, tended to be more competitive than the broadleaf weeds.  In some of our low diversity, no herbicide treatments, the lowest broadleaf biomass was recorded.  This is not as a result of fewer broadleaf weeds necessarily, but a side impact of high, and competitive, wild oat populations reducing the size and impact of the broadleaf weeds.

Soil nutrient cycling and soil microbial communities were primarily impacted by location, however there are some indications that use of chaff collection may also impact carbon and nitrogen cycling. This could lead to further impacts on greenhouse gas emissions and is an area that warrants additional research. Investigations into feed quality of chaff collections indicated potential use for chaff as a livestock feed. Variations across locations could be an impact from environmental conditions during crop growth, or composition of the chaff and the various weed species contained within it. This is an additional area of potential future research.

Overall, it is clear that IWM strategies, when combined, can reduce or eliminate herbicide use for up to three years in a cropping system. There are gaps in these strategies, however, when it comes to management of twining weeds. Additionally, there are potential side effects on nutrient cycling, microbial communities, and potential novel markets for weed management by-products based on some of these strategies, all of which require further research or investigation.