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Don’t Let Early-Emerging Weeds Derail Your Season

March 30, 2021
THis agronomic image shows lambsquarters

Common lambsquarters

You have many choices to make as a grower, and the right choices are those that will help you preserve your maximum genetic yield potential. With planting just around the corner, understanding weed emergence order will help you get a head start on weed management.

Good weed management goes beyond just understanding which weed species are already present or are likely to be present based on historic knowledge of your field; the Iowa State University Extension advises that it’s important to understand when they arrive each season. Weed emergence timing influences which species will be the most pressing in a given year, as well as how best to manage them.

Weeds can be sorted into groups depending on their emergence time. At this time of year, the ones to be most concerned with are Group 0 (winter weeds and biannuals) as well as Groups 1 and 2 (weeds which will emerge prior to planting, typically from February – April).

Here’s what to look for as you scout your fields before planting:

Marestail (Horseweed)

This agronomic image shows marestail

While this weed may germinate year-round in different geographies, it typically does so in the spring, late summer or fall. Knocking out this weed before its highly mobile seeds spread throughout your fields offers the best chance of management.

Look for:

  • A rosette soon after emergence.
  • Growth up to 6’ tall.
  • Leaves that decrease in size toward the top of the plant.

 Giant Ragweed

THs agronomic image shows giant ragweed

This large-seeded broadleaf can reach heights of up to 20’ and has a voracious appetite for the resources that your crop needs to maximize yield potential. On top of that, giant ragweed seeds germinate deep within the soil profile, making them especially difficult to manage.

Look for:

  • Thick, fleshy cotyledons.
  • Heavily lobed leaves that are rough to the touch.
  • Opposite leaf arrangement as the plant develops.
  • Weed height that is 1 – 5’ taller than the crop with which it is competing.

Common Lambsquarters

this agronomic image shows lambsquarter

This early-emerging weed is one of the most competitive species, particularly due to its rapid growth rate. Each plant produces an average of 72,500 seeds, which are some of the most resilient in the soil seed bank.

Look for:

  • Triangular and egg-shaped leaves that are a pale gray-green.
  • A white, powdery coating on leaf surfaces.
  • Small green flower clusters at the tips of the main stem.


this agronomic image shows velvetleaf

This species is common throughout the Midwest. It can produce 9,000 seeds per plant, and its hard seed coats give velvetleaf seeds longevity in the soil seed bank. Not only is it highly competitive with corn and soybeans throughout the year, it can also interfere with harvest due to its sturdy stems.

Look for:

  • Heart-shaped leaves that are 2 – 6” in length and covered in velvety hairs.
  • Stems that are also covered in hairs and emit an odor when crushed.
  • Typical plant height of 2 – 4’, but it could reach up to 8’ if left unchecked.

Effective Herbicide Programs for Managing Early-Season Weeds

Armed with the knowledge of your trouble weeds and their emergence timing, consider your management options. There are several residual herbicides available from Syngenta to cover a broad spectrum of early-emerging weeds.

In soybeans, Boundary® 6.5 EC, BroadAxe® XC or Prefix® herbicides all contain multiple effective sites of action and can help you stop early-season weeds in their tracks. These flexible options can be used with any trait platform, providing a dependable fit to address your specific field conditions and needs.

  • Boundary 6.5 EC delivers proven protection and residual control against 32 broadleaf weeds, including early-emerging lambsquarters, velvetleaf, common ragweed, shepherd’s purse and early-season grass weeds.
  • BroadAxe XC combines 2 effective sites of action for broad-spectrum activity against key broadleaf weeds, including early-emerging weeds such as Russian thistle, kochia and annual grass weeds, which are more common in the upper Midwest.
  • Prefix delivers extended residual activity – up to 5 weeks – against key grass and broadleaf weeds, including early-emerging marestail, lambsquarters, sunflower, giant foxtail and field pennycress.

When used as part of a system of overlapping residuals with cultural practices – such as early planting and narrow row spacing – these herbicides can help protect your fields from tough and resistant weeds all season long. In dicamba-tolerant soybeans, an overlapping application of Tavium® Plus VaporGrip® Technology herbicide, the first dicamba herbicide premix, early post-emergence can extend the residual performance of your program to prevent weed escapes.

To find out which soybean residual herbicide program will work best with your trait, use the soybean herbicide program planning tool.

In corn, Acuron® herbicide provides season-long control of more than 70 weeds and grass, including early-emerging marestail, lambsquarters, velvetleaf and grass weeds. And, when applied preemergence and at full labeled rates, Acuron outyields all other corn herbicides by 5-15 more bushels an acre because of its unique combination of powerful weed management, longest-lasting residual and proven crop safety.*

Knowing which weeds to expect and when to expect them can help you map out a full-season approach to manage the right weeds at the right time with the right solutions.

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*When applied preemergence and at full label rates. Acuron yield advantage range based on 2016 Syngenta and University trials comparing Acuron to Corvus®, Resicore®, SureStart® II and Verdict®. For more information on Acuron versus an individual product, ask your Syngenta representative.