Weed seed shatter in spring wheat in Alberta

Harvest weed seed control is a new method of weed control developed in Australia that targets weed seeds that would otherwise be spread by the combine harvester. How well harvest weed seed control works depends on what percentage or proportion of seeds produced by the target weeds are still on the plant versus already dropped to the soil. This study investigated seed shatter of nine weed species: wild oat, green foxtail, wild mustard, cleavers, spiny annual sow thistle, lambsquarters, redroot pigweed, round-leaved mallow, and kochia. Seed shatter (seeds dropped to the soil) was measured for each of these species in spring wheat from 2014 to 2016 near Lacombe and Lethbridge, AB. Measurements were taken in small plot studies, or in producer fields. Seed shatter was measured through use of shatter trays that were collected approximately weekly during crop ripening, with plant harvests to assess number of seeds produced and retained also conducted at swathing and direct-harvest (direct-combining) stages. Seed shatter was considered low if the plant had lost less than 20% of produced seeds and high if the plant had lost more than 80% of its seed by the direct-harvest stage. Green foxtail, lambsquarters, kochia and round-leaved mallow were measured to have low seed shatter, and therefore are more likely to make good targets for harvest weed seed control. Wild oat and annual sow thistle had high seed shatter and are likely to make poor targets for harvest weed seed control. Wild mustard, cleavers, and redroot pigweed were considered intermediate targets for harvest weed seed control. Seed retention of most species was improved by swathing. Potential for harvest weed seed control in western Canada is species specific, but may work well for intermediate and good target species identified above.