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Weed Wisdom March 2017


Narrow-Leaved Hawk’s-Beard (Crepis tectorum)

Crepis tectorum by BLM/AKNHP 2010

The weather conditions in many areas last fall made it difficult to control winter annual weeds and extra attention may be warranted this spring. One such weed to consider is narrow-leaved hawk’s-beard (Crepis tectorum). It used to be considered primarily a weed of the northern Canadian prairies but is now also firmly established as a weed of the brown and dark brown soil zones. A recent weed survey found it to be the 9th most abundant weed in Saskatchewan.

Narrow-leaved hawk’s-beard is an annual or winter annual species that reproduces by seed. It is capable of germinating at low soil temperatures (5 C) and thus can easily establish in late fall or early spring. It readily germinates on or near the soil surface so it is well adapted to reduced tillage cropping systems. Early growth consists of a rosette of leaves with individual leaves being pointed and lobed, 2-4 cm wide, and 10-15 cm long. 

Rosettes can sometimes be confused with those of dandelion but dandelion leaves have a shinier surface and are a darker green colour. Hairless stems containing a milky white sap attain heights of 60-100 cm with bright yellow flowers.

Crepis tectorum rosette

Seeds are 2.5-4 mm long, ribbed, and purplish-brown to purple with a tuft of white hairs. Seed dissemination is widespread due to the seed hairs facilitating movement by wind and water plus the rough ribbed seeds adhere to animals and are distributed with their movement. Seed has little dormancy so it readily germinates after reaching maturity.

Narrow-leaved hawk’s-beard can be quite competitive with crops depending on its emergence timing and infestation density. Overwintering plants resume growth in April and its deep taproot can consume considerable amounts of soil nutrients and water before control measures can be implemented. Emphasis should be placed on controlling seedlings in fall as larger, overwintered plants are more difficult to control. Consider higher glyphosate rates or preferably add a tank-mix partner to your spring glyphosate burndown. There are several herbicides available for in-crop control in cereals, but timing is critical as bolted plants are unlikely to be controlled. While not widespread, Group 2 resistant narrow-leaved hawk’s-beard populations have been documented in Alberta. Thus, careful herbicide selection and application timing is required for this tough-to-control weed.