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Test Your Corn and Soybean Weed Identification Skills

July 14, 2020

Think you know tough weeds? This quiz can help you get the most out of your in-season field scouting. Give it a try, then scroll to the bottom of this post for the answers.

This agronomic image shows a range of corn and soybean weeds

Can you name them all? If you need a hint, look for these distinguishing features of some of the toughest weed species:


According to Michigan State University Extension and Take Action, season-long competition from waterhemp can reduce soybean yield by 44%. On top of that, just 1 late-season waterhemp plant can deposit up to 1 million seeds into the soil, causing future problems.

Look for:

  • Absence of hair.
  • Glossy and elongated leaves.
  • Stem color that varies from light green to dark red.

Palmer Amaranth

Out of many tough weed species to scout for, this pigweed is one of the most unpredictable – it can emerge at any point in the season. Due to its erratic nature, begin scouting for Palmer amaranth early and continue throughout the year.

Look for:

  • Diamond-shaped leaves varying from green to pink.
  • Seed heads that grow up to 30” long.
  • Possible white, V-shaped markings on the leaves.

Marestail (Horseweed)

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

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

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 control.

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 Cocklebur

At the seedling stage, this weed is easily confused with giant ragweed, because the long cotyledons of the 2 species look similar. However, giant ragweed emerges several weeks prior to corn and soybean planting, whereas common cocklebur emerges closer to the end of planting. Cocklebur’s large leaves intercept a lot of sunlight, making it highly competitive and a yield reducer.

Look for:

  • Leaves that are approximately 2 – 6” in length and triangular or ovate in shape.
  • Stiff hairs on the surface areas of the leaves.
  • Three veins extending from the same point on the upper side of the leaf.
  • Long petioles.

Common Lambsquarters

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.

Our Recommendations

Be sure to choose the correct herbicide program for the weed challenges in your fields.

For soybeans, we recommend a strong preemergent herbicide, such as Boundary® 6.5 EC, BroadAxe® XC or Prefix® herbicides. Tavium® Plus VaporGrip® Technology herbicide is an effective early post-emergent option in dicamba-tolerant soybeans for controlling a broad spectrum of tough broadleaf and grass weeds. Delivering 2 effective sites of action, it also helps with weed resistance management. Tavium is the market’s first and only premix dicamba herbicide that provides both contact and residual control of weeds.

For corn, Acuron® herbicide delivers 5-15 more bushels an acre when used preemergence at full label rates by controlling the tough weeds that other products miss*. Acuron has unmatched application flexibility, from 28 days preplant up to 12” corn. It can be followed by a post-emergence application of Halex® GT corn herbicide**, for a program that provides 4 total sites of action for resistance management.

Visit ResistanceFighter.com or talk to your local Syngenta retailer or sales representative about knocking out tough and resistant weeds in your area.

Weed ID Quiz Answers

A: Common lambsquarters

B: Giant ragweed

C: Waterhemp

D: Common cocklebur

E: Palmer amaranth

F: Marestail (horseweed)

Did you name all the weeds correctly? Let us know!
  • Yes, I got them all! 80%, 24 votes
    24 votes 80%
    24 votes - 80% of all votes
  • I almost got them all! 20%, 6 votes
    6 votes 20%
    6 votes - 20% of all votes
Total Votes: 30
July 15, 2020 - August 16, 2020
Voting is closed

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

** Halex GT should be tank mixed with atrazine or dicamba. When applying Acuron followed by Halex GT, Acuron should be applied 1.25-1.5 qt/A, depending on soil type and organic matter.