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Weed Wisdom April 2018


by Dr. Charles Geddes

green foxtail
An emerging Green Foxtail plant in southern Alberta

Compared to normal, we certainly are experiencing a late spring this year.  What impact will this have on weeds? Good question…

Weed seeds in the soil seedbank rely on environmental cues for germination.  These cues include the temperature, moisture availability, light spectrum, and chemical solution (including nutrients) in the seed’s immediate vicinity. 

Adult Green Foxtail
Adult Green Foxtail growing in southern Alberta.

In many cases, these cues also govern the release of seed dormancy prior to germination. They are also the reason why different weed species have different emergence periodicity (the timeframe in which they germinate and emerge in a given year) because the ideal temperature and moisture availability for germination and dormancy alleviation

can vary among weed species. 


In southern Alberta, for example, kochia (Kochia scoparia) is often one of the first weed species to emerge in the spring.  This is because the base temperature (lowest possible temperature) at which kochia can germinate and emerge from the soil seedbank is quite low (below 2.2°C). For comparison, green foxtail (Setaria viridis) has difficulty germinating at 10°C, requiring about 60 days to reach maximum germination at this temperature.

young Kochia
Kochia emerging from soil in southern Alberta

 To make a long story short, if a late spring also indicates more rapid warming of the soil when spring does arrive, many weed species could be emerging at the same time, rather than a more drawn out distribution of weed emergence under typical conditions.

If we have a cold spring, weeds that thrive under cool conditions may dominate our weed populations. At this point, it is difficult to predict the effect that our delayed spring conditions will have on weeds this year. However, greater than normal snowfall over the winter in southern Alberta likely also had an insulating effect on field soils, potentially buffering the weed seedbank from loss of seed viability due to cold temperatures. The insulating effect of snow has been shown to increase persistence of weed seeds, like volunteer canola (Brassica napus), in the soil seedbank. Hopefully, warmer days lay ahead. Like many farmers in southern Alberta, I am itching to get out in the field. 

Adult Kochia
A thriving Kochia plant growing in a southern Alberta field.