Sow-Thistle, Annual
(Sonchus oleraceus L.)

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Table of Contents

1. History
2. Life Cycle
3. Distinguishing Characteristics
4. Control in Corn
5. Control in Soybeans
6. Control in Winter Wheat

History

A member of the composite or aster family and a very come weed in many of the field crops in Ontario. Annual sow-thistle was one of the first weeds added to the Noxious Weed List under the Ontario Weed Control Act.

Life Cycle

Annual, reproducing only by seed.

Distinguishing Characteristics

Spiny annual, annual and perennial sow-thistle are often confused with one another. Perennial sow-thistle can be differentiated from sow-thistle as it will be the first to emerge in the spring and will have an extensive underground root system. The leaves of perennial sowthistle are also not as deeply lobed as annual sow-thistle. Spiny annual sow-thistle can be differentiated from annual sow-thistle by its dark green leaves with purplish margins. The leaves of spiny annual sow-thistle also look and feel extremely waxy. Spiny annual sow-thistle is also more "spiny" or "prickly" to the touch versus annual sow-thistle. Lastly, spiny annual sow-thistle has leaves which have rounded basal lobes that clasp around the stem.

Annual Sow-thistle Pictures
Each thumbnail image links to a larger image

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Herbicide Control in Field Corn

Pre-Plant Control:

Glyphosate is very effective on annual sow-thistle, however a pre-plant application of glyphosate at 1 L/ac will not offer season long control of annual sow-thistle as it has no "residual" to control secondary flushes of this weed. Therefore glyphosate with the addition of a soil-applied residual herbicide should give good control of annual sow-thistle beyond the critical period for weed control (Table 1).

Post Emergent Control

Glyphosate provides excellent control in "Roundup Ready" corn. In conventional corn, the high rate of BANVEL II or PEAKPLUS will provide supression of this weed (Table 2). Although Table 2 identifies the % control rating for LIBERTY as only 65%, LIBERTY does provide very good initial control of annual sow-thistle. However, secondary flushes of annual sow-thistle are not uncommon since LIBERTY offers no "residual" activity and thus the reason for that rating.

Some have commented that these visual control ratings are somewhat contradictory to what is in OMAF Publication 75 - Guide to Weed Control, however only herbicide performance ratings exist for perennial sow-thistle in that publication, which may or may not be applicable to annual sow-thsitle.

Source:

Dr. Peter Sikkema, Ridgetown College, University of Guelph.

Number of Trials:

Table 1 is based on a summary of 1 field trial.
Table 2 is based on a summary of 2 field trials.

Herbicide Rates:

Rates used in this trial are listed in OMAF Publication 75 - Guide to Weed Control.

Weed Stage:

Annual sow-thistle was around the 7 leaf stage (10 cm. in height) at the time of application.

What has been your experience?

We want your feedback. Let us know what you have experienced with these or other products, as well as any other effective management strategies.

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Herbicide Control in Soybeans

A pre-plant application of glyphosate at 1 L/ac will provide good control of annual sow-thistle that has emerged at the time of application. However since glyphosate has no "residual" activity, it will not control any secondary flushes of this weed. Therefore in "Roundup Ready" soybeans, a second application of glyphosate will be required to control annual sow-thistle. If growing conventional soybeans, CLASSIC applied post-emergent, offers the most consistent level of annual sow-thistle control, while FIRSTRATE can also provide good supression/control (Table 1).

Source:

Dr. Peter Sikkema, Ridgetown College, University of Guelph.

Number of Trials:

Table 1 is based on a summary of 3 field trials.

Herbicide Rates:

Rates used in this trial are listed in OMAF Publication 75 - Guide to Weed Control.

Weed Stage:

Annual sow-thistle was around the 7 leaf stage (10 cm. in height) at the time of application.

What has been your experience?

We want your feedback. Let us know what you have experienced with these or other products, as well as any other effective management strategies.

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Herbicide Control in Winter Wheat

Refer to Table 8-1 in OMAF Publication 75 - Guide to Weed Control for herbicide ratings on this species.

What has been your experience?
We want your feedback. Let us know what you have experienced with these or other products, as well as any other effective management strategies.