Harvest weed seed control of Italian ryegrass [Lolium perenne L. ssp. multiflorum (Lam.) Husnot], common ragweed (Ambrosia artemisiifolia L.), and Palmer amaranth (Amaranthus palmeri S. Watson)

Abstract

Herbicide resistance is a major problem in United States and global agriculture, driving farmers to consider other methods of weed control. One of these methods is harvest weed seed control (HWSC), which has been demonstrated to be effective in Australia. HWSC studies were conducted across Virginia in 2017 and 2018, targeting Italian ryegrass in continuous winter wheat as well as common ragweed and Palmer amaranth in continuous soybean. These studies assessed the impact of HWSC (via weed seed removal) on weed populations in the next year’s crop compared with conventional harvest (weed seeds returned). HWSC reduced Italian ryegrass tillers compared with the conventional harvest at two locations in April (29% and 69%), but no difference was observed at a third location. At wheat harvest, HWSC at one location reduced Italian ryegrass seed heads (41 seed heads m−2) compared with conventional harvest (125 seed heads m−2). In soybean, before preplant herbicide applications and POST herbicide applications, HWSC reduced common ragweed densities by 22% and 26%, respectively, compared with the conventional harvest plots. By soybean harvest, no differences in common ragweed density, seed retention, or crop yield were observed, because of effectiveness of POST herbicides. No treatment differences were observed at any evaluation timing for Palmer amaranth, which is attributed to farmer weed management (i.e., effective herbicides) and low weed densities making any potential treatment differences difficult to detect. Across wheat and soybean, there were no differences observed in crop yield between treatments. Overall, HWSC was demonstrated to be a viable method to reduce Italian ryegrass and common ragweed populations.

Harvest Weed Seed Control: Seed Production and Retention of Fallopia convolvulus, Sinapis arvensis, Spergula arvensis and Stellaria media at Spring Oat Maturity

“…The efficiency of HWSC relies on the proportion of the weed seed production that is retained at crop maturity [34]. Seed retention higher than 80% at crop maturity happens for many agronomically important weed species creating a unique opportunity to target these weed seeds and prevent them from becoming a part of the weed seed bank in the soil [34]. Delays in crop harvest can result in fewer weed seeds being captured because of a higher rate of seed shatter [35,36].…”

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

“…In HWSC studies conducted across Virginia, up to 70% reductions in population densities of L. perenne ssp. multiflorum and ~ 24% reduction in Ambrosia artemisiifolia L. were observed in the following crop compared with conventional harvest 26 . However, effective management with herbicides under low weed seed pressure conditions rendered differences between HWSC and conventional harvest undetectable.…”

“…multiflorum and ∼ 24% reduction in Ambrosia artemisiifolia L. were observed in the following crop compared with conventional harvest. 26 However, effective management with herbicides under low weed seed pressure conditions rendered differences between HWSC and conventional harvest undetectable. Integrated use of propoxycarbazone and chaff collection during winter wheat harvest has been shown to reduce Lolium perenne L. ssp.…”

“…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.…”

“…Linking the soil seed bank to the emerged weed community has proved elusive 24 . Nonetheless, some North American HWSC studies have observed emerged weed population reductions after a single HWSC event 25,26 . One modeling study has shown that > 80% of newly shed A. fatua seed must be eliminated to stop the population increasing, resulting in a stable population 27 .…”