Weed seed shatter in spring wheat in Alberta

The efficacy of harvest weed seed control depends on the extent of seed shatter of the targeted weeds. Seed shatter of nine weed species, namely, wild oat (Avena fatua L.), green foxtail [Setaria viridis (L.) P. Beauv.], wild mustard (Sinapis arvensis L.), cleavers (Galium spurium L. and G. aparine L.), spiny annual sow thistle [Sonchus asper (L.) Hill], lambsquarters (Chenopodium album L.), redroot pigweed (Amaranthus retroflexus L.), round-leaved mallow (Malva pusilla Sm.), and kochia [Kochia scoparia (L.) Schrad.] was measured in spring wheat (small-plot trials or producer fields) from 2014 to 2016 near Lacombe and Lethbridge, AB. Seed shatter was assessed using shatter trays collected periodically during crop ripening, as well as at the swathing and direct-harvest (direct-combining) stages. If ≤20% and ≥80% seed shatter by the direct-harvest stage is considered low and high, respectively, then green foxtail, lambsquarters, kochia, and round-leaved mallow are classified as low, wild oat and annual sow thistle as high, and the other investigated species classed as intermediate. Seed retention of most species was improved by swathing compared with direct-combining. Study results indicate that harvest weed seed control practices have good potential for several weed species in western Canada.