Lamb’s-quarters is one of the most common weeds found in Ontario. In 2016 it ranked as Ontario’s worst weed in a University of Guelph survey and it consistently ranks in the top five most troublesome and popular weeds. To make matters worse, herbicide resistant populations are spreading throughout Ontario. As early as 2016, Group 2- and 5-resistant biotypes were documented in Ontario and some farmers are also reporting variability in control from their glyphosate application. If left untreated lamb’s-quarters can cause yield loss of up to 38% in soybeans and 35% in corn.
Early season control matters
The best time to manage lamb’s-quarters is in the fall or early spring. Herbicides will perform better on the weed before the plant reaches 10 cm in height, and glyphosate control is most consistent when the plant is less than 2.5 cm tall1.
Below is a chart from the 2017 OMAFRA Weed Guide showing farmer’s opinions of glyphosate control of lamb’s quarters in relation to the size of the weed.
OMAFRA 2017 Weed Guide
Since the germination window can stretch several weeks the best spring herbicide strategy should combine both contact and soil active residual herbicides.
Lamb’s-quarters is a weed that is best managed through a multi-pronged herbicide program. Before planting soybeans consider applying BlackHawk® with a pre-emergent residual herbicide and glyphosate. BlackHawk and glyphosate will act quickly on the early emerged lamb’s-quarters while the pre-emergent product will have activity on later emerging weeds. This is also a solid weed resistance management strategy, applying multiple modes of action to the weed seed bank slowing the adoption of herbicide-resistance and protecting the efficacy of the herbicides for future years.
BlackHawk is an excellent fall or spring burndown product for controlling actively growing lamb’s-quarters. It combines two complementary active ingredients: 2,4-D ester (Group 4) and pyraflufen-ethyl (Group 14). This combination provides fact activity on lamb’s-quarters and many other broadleaf weeds. BlackHawk also makes an excellent tank-mix partner with many pre-emergent herbicides as well as glyphosate.
1. OMAFRA 2017 Weed Guide
Always read and follow label directions.
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