Common Lambsquarters in Field Crops
Common Lambsquarters (Chenopodium album L) is one of the most prevalent summer annual broadleaf weeds in North America. Of particular concern agronomically is how this species of weed has developed resistance and tolerance to different herbicide choices so readily. Of historical note, Triazine (Atrazine, Bladex, Princep) Resistant Lambsquarters were one of the first herbicide resistant weeds discovered back in the 60’s-70’s.
Often confused with or referred to as Pigweed (Amaranthus spp), Lambsquarters is frequently found persisting in fields alongside its mis-identified neighbor--they both tend to thrive in similar field situations, histories, and crops, but are actually quite different. The leaves of Lambsquarters appear lance-shaped, triangular, or diamond shaped and as they emerge, they exhibit a gray, almost silver, mealy coating across the leaf surfaces, which gives them away.
Lamsquarters Identification and Impact
Technically, the most similar looking weed to Lambsquarters is actually Atriplex (Atriplex patula L.). They differ by Atriplex having larger cotyledons, a more branching, spreading habit due to the opposite arrangement of the first several pairs of leaves and branches, and leaf bases with a lobe on each side.
Uniquely, Common Lambsquarters’ germination and emergence can be spread over 2-3 months, and even longer. Peak emergence is in mid to late spring. Though not as significant, they can germinate and emerge well into the summer. Once emerged, Lambsquarters grows very rapidly, making it particularly troublesome in soybeans. Data suggests that as little as one lambsquarter plant per foot of row can reduce soybean populations by as much as 25%. In heavy infestations, lambsquarters in soybeans are particularly annoying to combine operators as they readily clog the equipment at harvest when left unabated.
Perhaps the most significant fact about lambsquarters, leading to its infamous reputation with resistance and tolerance, is that a single plant produces an average of over 70,000 seeds with wide variance in dormancy indices, depending on the relative depths of the seedbank. This persistence is the cornerstone to causing headaches for farmers and advisors alike. On average, it takes 12 years to deplete the seed bank by 50% and nearly 80 years to approach elimination (99%).
Control programs and scouting for lambsquarters should focus on the spring germinating populations. Because of its rapid growth once emerged, planting into a soil where lambsquarters is visible will be problematic. The existing population must be burned down or tilled prior to planting. Once it establishes, it can rapidly develop and rob nutrients and moisture from the desired crop. Later germinating lambsquarters in corn that has formed its canopy over the row, for example, will not likely be an economic threat; but if it grows along with the germinating corn seed, it will ‘pace’ the corn for light, water, and nutrients and can be a real problem.
Resistance and Tolerance Management
Regardless of the nature of the lambsquarters populating your fields, understanding its life cycle and relative presence or absence in your crops is the key to managing it economically. Tillage; crop rotation; and herbicide rotation are and will always be your best approach. Good recordkeeping of what materials have been used in a field, matched with observations from field scouting, and planning short rotations will come together to lessen the impact of this troublesome weed pest.