Seed retention of winter annual grass weeds at winter wheat harvest maturity shows potential for harvest weed seed control

Abstract

Downy brome, feral rye, and jointed goatgrass are problematic winter annual grasses in central Great Plains winter wheat production. Integrated control strategies are needed to manage winter annual grasses and reduce selection pressure exerted on these weed populations by the limited herbicide options currently available. Harvest weed-seed control (HWSC) methods aim to remove or destroy weed seeds, thereby reducing seed-bank enrichment at crop harvest. An added advantage is the potential to reduce herbicide-resistant weed seeds that are more likely to be present at harvest, thereby providing a nonchemical resistance-management strategy. Our objective was to assess the potential for HWSC of winter annual grass weeds in winter wheat by measuring seed retention at harvest and destruction percentage in an impact mill. During 2015 and 2016, 40 wheat fields in eastern Colorado were sampled. Seed retention was quantified and compared per weed species by counting seed retained above the harvested fraction of the wheat upper canopy (15 cm and above), seed retained below 15 cm, and shattered seed on the soil surface at wheat harvest. A stand-mounted impact mill device was used to determine the percent seed destruction of grass weed species in processed wheat chaff. Averaged across both years, seed retention (±SE) was 75% ± 2.9%, 90% ± 1.7%, and 76% ± 4.3% for downy brome, feral rye, and jointed goatgrass, respectively. Seed retention was most variable for downy brome, because 59% of the samples had at least 75% seed retention, whereas the proportions for feral rye and jointed goatgrass samples with at least 75% seed retention were 93% and 70%, respectively. Weed seed destruction percentages were at least 98% for all three species. These results suggest HWSC could be implemented as an integrated strategy for winter annual grass management in central Great Plains winter wheat cropping systems.

Current outlook and future research needs for harvest weed seed control in North American cropping systems

“…have high seed retention at crop maturity. 8 Similarly, in Canada, problematic weeds of cereal, oilseed, and pulse crops, Setaria viridis (L.) P. Beauv., Chenopodium album L., and Bassia scoparia (L.) A. J. Scott, retain a high proportion of seed at crop maturity and thus are good candidates for HWSC control.…”

“…19 In eastern Colorado, a high proportion (> 75%) of seed was retained by A. cylindrica and B. tectorum at wheat maturity. 8 In 2013, a field survey of winter wheat fields near Pullman, WA found that 58% of seeds of Lolium perenne L. ssp. multiflorum (Lam.)…”

“…Conversely, winter annual grasses appear to be better suited for management with HWSC. 8,26,36 Among broadleaf weeds, species such as Erigeron canadensis L. and Taraxacum officinale F. H. Wigg. that disperse seeds by wind prior to harvest are also not good targets for HWSC.…”

“…Winter wheat production in the U.S. Northern Great Plains and Pacific Northwest is plagued by winter annual weed species; Bromus tectorum L., and Aegilops cylindrica Host. have high seed retention at crop maturity 8 . Similarly, in Canada, problematic weeds of cereal, oilseed, and pulse crops, Setaria viridis (L.) P.…”

Seed retention of ten common weed species at oat harvest reveals the potential for harvest weed seed control

“…of their retained seeds might be reduced due to their stem growth type and seed set along the entire stem. Weed species of similar or taller height than the crop will increase the seed collection efficiency at harvest (Soni et al, 2019). It is also likely that some seeds spread and fall to the soil surface during the harvesting process.…”