At high densities, smartweed can cause significant yield reductions in cereal and oilseed crops.

Smartweed seedlings
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Smartweed juvenile plant Smartweed plant and root Smartweed leaf
Smartweed ochrea on stem Smartweed flowering seed head Smartweed flowers Smartweed seeds


This weed is an annual that reproduces by seed. Stems are branched, up to 80 cm (30 in.) tall and hairless. The leaves are stalked and tapering towards both ends. They are widest near the middle, up to 8 cm (6 in.) long and 1.5 cm (1/2 in.) wide. The lower leaves are hairless. Some of the leaves may have a reddish 'thumb print'. The base of the leaf stalk has a papery sheath surrounding the stem. The sheath is hairless. The flowers are grouped into dense clusters at the ends of the stems and on short stalks arising from the bases of the upper leaves. The flowers are usually green.

Smartweed produces about 3,000 seeds per plant. It prefers to grow in moist soil conditions and is most common near ponds, dug-outs, and sloughs, especially in the parkland regions.

Scouting Techniques

Take a minimum of 20 weed counts across the field. Check any low spots for patches of this weed because it prefers moist conditions. Annual smartweed is often confused with perennial smartweed, which also occurs in wet spots.

Effects On Crop Quality

Large plants may take a long time to dry in the swath and delay harvesting. Smartweed seed is difficult to clean out of flax.

Threshold/Yield Loss

Smartweed can reduce wheat yields by 30-35% when weed densities are greater than 150-200 plants per square metre (sq. yd.). If the weed emerges 7-14 days after the crop, yield reductions are usually not significant.

Densities of 15-20 plants per square metre (sq. yd.) in canola will reduce yields by 4-5%. If densities reach 100-200 plants per square metre (sq. yd.), yields may be reduced by 25-50%.

Control Tips

Consider growing crops like cereals, canola, and peas on fields with serious smartweed infestations as they offer stronger competition and more effective herbicide options than flax, lentils and other special crops.