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Weed Wisdom May 2018


Seeding Date Diversity Helps Control Weeds

with files from Dr. Charles Geddes

Too bad Shepherds Purse doesn’t grow with money inside! We’d all be rich.

Don’t fret about a late spring or getting seed in the ground later this year than last. After all, it could help add diversity to your weed management program. Dr. Geddes recommends producers vary seeding dates in a particular field year over year. This will help reduce selection pressure for early- or late-emerging weed species. Planting time diversity can work wonders for weed management and keeping weeds on their toes can pay dividends later on.

Early seeding gives the crop time to get ahead of the weeds in the soil seed bank. This makes the crop a stronger competitor and out of its vulnerable early growth & development stages before the weeds emerge. Early crop establishment often results in greater crop yield. Canola is an excellent example of this.  At four of 10 sites-years in Alberta, seeding canola in late-April to early-May resulted in greater yield compared with seeding dates closer to mid-May (Clayton et al. 2004). 

Russian thistle will also show up in southern Alberta fields.

Even when the pre-seed burndown treatment allows weeds to emerge after planting that doesn’t always cause greater yield loss. In a barley-field pea rotation near Lacombe, Alberta, field pea seeded in April yielded greater than May seeded in three of four years. Even though the early seeding date often had greater weed biomass (Blackshaw et al.  2005).

Conversely, later seeding dates allow for later pre-seed burndown or a stale seedbed technique that can capture more emerged weeds. The crop can end up with less weed biomass and  competition.

Round leaf mallow comes up early and has a tap root.


Blackshaw RE, Moyer JR, Harker KN, Clayton GW (2005) Integration of agronomic practices and herbicides for sustainable weed management in zero-till barley field pea rotation. Weed Technology 19:190-19

Clayton GW, Harker KN, O’Donovan JT, Blackshaw RE, Dosdall LM, Stevenson FC, Ferguson T (2004) Fall and spring seeding date effects on herbicide-tolerant canola (Brassica napus L.) cultivars. Canadian Journal of Plant Science 84:419-430