Target Grade Level / Age Range:


Estimated Time:

45 minutes – 1 hour


Students will gain an understanding of the definition of an invasive species, and what impacts invasive species pose to farmers.


  • Access to the Internet
  • Student laptops, computers, or tablets to complete the online game included below
  • Deck of playing cards

Vocabulary (with definitions)

  • I nvasive species: a species that is 1) non-native (or alien) to the ecosystem under consideration and 2) whose introduction causes or is likely to cause economic or environmental harm or harm to human health (USDA)
  • Pal mer amaranth: an annual broadleaf weed in the amaranth genus which is only native to the Southwest and is considered a weed throughout the United States (USDA). Also called: carelessweed, dioecious amaranth, Palmer’s pigweed

Background – Agricultural Connections (what would a teacher need to know to be able to teach this content)

Why Invasive Species are Harmful to Farmers

  • Significantly impacts the yield, or overall production of crops
  • It is estimated that Palmer amaranth can reduce corn yields up to 91 percent, and soybean yields up to 79 percent
  • Invasive species “choke out” native species and crops farmers have planted. With the ability to spread far, fast, and wide, invasive species are sometimes deadly to crops.
  • Palmer amaranth specifically:

Preventative Measures

  • Herbicides: Farmers can apply herbicides, or chemicals that target weeds and invasive species.
    • These applications do not harm crops, but significantly damage and kill invasive species. By using herbicides, farmers can prevent losing significant portions of their crop yield.
    • Downfall to herbicides: potential resistance
      • Resistance refers to a weed’s ability to live and reproduce effectively after treatment intended to eliminate it. Plants can become resistant through evolutionary changes. Weeds are more likely to develop evolutionary resistance when then are repeatedly and consistently treated with herbicides from the same inhibitory action group. Each inhibitory action group targets a different part of a plant’s anatomy or physiology. This link lists the action groups:
      • Resistance of Palmer amaranth: Primarily due to high genetic diversity, some Palmer amaranth is resistant to multiple herbicides. In addition, some Palmer amaranth seed arrives already resistant to multiple herbicides. This is due to its spread from the southwest United States, were several herbicides have been used in an attempt to control it.
  • Tillage: Farmers are able to use equipment to overturn soil, uprooting any potential weeds. Tilling is also used to incorporate some fertilizers, such as manure, into the soil. The tillage process is useful for eliminating weeds but can lead to negative outcomes as well.
    • Negative: Tilling can increase soil erosion in a field. This is harmful to a field because erosion washes away some of the topsoil, which is uppermost layer of soil. The topsoil is typically rich with organic matter from the previous year’s crop remnants.
    • Positive: Tilling provides farmers another preventative measure against weeds. In addition, tillage is a great option for organic farmers, who are not permitted to use traditional herbicides for weed management.

Interest Approach – Engagement (what will you do to engage students at the beginning of the lesson)

Have students play this game as an introduction to invasive species and their impacts. This game explains the invasion of Asian carp into the Great Lakes. Students will progress through the game, making choices on how to minimize the impact of the invasive Asian carp. Students will be able to observe that some of their choices, despite the positive intention, have potential to produce an additional negative outcome.       

Link to game:

Have students discuss the following questions in pairs, groups, or a whole class:

  • What are some behavior characteristics of the Asian carp?
  • What are the impacts of the Asian carp? How did their behavior contribute to their impacts?
  • How did you try to keep Asian carp from invading?
  • Did you face any unexpected challenges?
  • What did you learn about invasive species from this game?


  1. After students have completed the game and the corresponding discussion, ask them to define an invasive species. Post the students’ definition where students are able to view it.
  2. Introduce students to the Palmer amaranth species and why it poses an issue to local farmers.
    1. Chokes out crops
    2. Damages farmers’ yield
    3. Proliferates extremely fast. Each Palmer amaranth plant can release from 500,000 up to 1 million seeds!
    4. Ask students: Why is this an issue?
  3. Explain the purpose and function of herbicides.
    1. Herbicides attack weeds and other invasive species in a field. Farmers often spray their crops with herbicides to stop the growth of weeds.
    2. Some of the crops farmers plant are resistant to herbicides, meaning herbicides do not harm the growth of the crop. However, this is not always the case. Some types of crops are not resistant to herbicides, meaning farmers would have to find an alternative method for weed management.
    3. An example of a crop that IS resistant to an herbicide is Roundup Ready Corn. Monsanto, an agriculture company, introduced this in 1998.
  4. Explain the purpose and function of fertilizers.
    1. Just like humans, all plants need nutrients in order to grow. Fertilizers provide essential nutrients to farmers’ crops.
    2. This can help increase yields and make stronger, healthier crops.
  5. Complete the activity with students described below. This activity is similar to the game Mafia.
    1. Note: The maximum number able to participate in this game at one time is 52 students, plus one moderator.
    2. This video does a great job of explaining the basis of the game. However, feel free to alter number of various types of players based on class size.
    3. Take a deck of 52 playing cards and sort out two face cards of each type (Kings, Queens, and Jacks) from the deck. Kings will be the “killers” (Palmer amaranth), Queens will be “police” (herbicides), Jacks will be “doctors” (fertilizer). All other cards with represent the crops in a field, such as corn or soybeans. Hand out facedown cards to students randomly, ensuring to hand out two of each face card. Ask students to look at their card, but not to share with anyone else. The number of Kings, Queens, and Jacks can be modified to fit class size.
    4. When all students have a card, ask them to place their heads down on their desks. Next, ask students who represent Palmer amaranth (Kings) to open their eyes. Together, they will silently pick another student to eliminate. Ask those students to put their heads back down.
    5. Next, ask students who represent herbicide (Queens) to open their eyes. Working together, they will try to determine which students represent Palmer amaranth. Students get one guess. If they guess correctly, the student who represents Palmer amaranth is eliminated. If not, the game continues. Ask students to put their heads back down.
    6. Ask students who represent fertilizer (Jacks) to open their eyes. These students will choose another student they want to save. The teacher then confirms whether they correctly identified the Palmer amaranth’s target. If they guessed the student correctly, s/he is saved. If not, the student will still be eliminated. Ask students to put their heads back down.
  6. Now, ask all students to open their eyes. Create a story as to how the student picked by the Palmer amaranth students was eliminated. For example:
    1. A local farmer planted corn in a field this spring. One day, when the farmer went to check on crops, he discovered Palmer amaranth had taken over a portion of the field. As he looked closer, he noticed some of his corn had been smothered out. I’m sorry student name , but you have been eliminated by the invasive species Palmer amaranth!
    2. There will be an alternative ending, depending on if fertilizers (Jacks) correctly identified the student targeted by the Palmer amaranth students (Kings):
      1. A local farmer planted corn in a field this spring. One day, when the farmer went to check on crops, he discovered Palmer amaranth had taken over a portion of the field. The farmer was thankful he had previously applied fertilizer to the field. Student targeted by Palmer amaranth , you were targeted by Palmer amaranth, but survived due to fertilizer (Jacks).
    3. Stories can be changed to fit the scenario and to interest students.
  7. Ask students if they have any guesses as to who represents the Palmer amaranth. Students can make arguments and debate. If students want, they can pick someone to eliminate. The student who is eliminated now watches the whole game.
  8. Students can also choose to reveal their identities. For example, if the herbicides (Queens) correctly identify the Palmer amaranth (Kings) during their turn, they may choose to accuse that students. They can reveal their identity to support the argument. For example, a student may say, “We should eliminate John. I know he is Palmer amaranth, because I am the herbicide.”
  9. The game repeats from step 7 until all the crops have been eliminated, or students have correctly identified the Palmer amaranth.
  10. After the game, discuss with students. How realistic is the activity to what actually happens in farmers’ fields? Explain how the game represents how difficult it is to completely eliminate an invasive species, even with the help of modern farming techniques.
    1. What challenges were there within the game? Does this correlate to challenges farmers may face?
    2. Why do you think herbicides were/were not effective? Is this an accurate representation of herbicide resistant crops?
    3. What do you think was the primary reason(s) crops/Palmer amaranth won the game? What parallels can be draw between these explanations and actual invasive species control and prevention.
  11. To incorporate a mathematical model into the lesson, ask students to compute and graph how exponentially Palmer amaranth reproduces. For example, in the article linked below, a particular sample of Palmer amaranth showed an 88 percent survival rate.
    1. Suppose a field contained 10 Palmer amaranth plants. Due to such small numbers of the weed, the farmer did not notice. The Palmer amaranth therefore grow to maturity and are able to reproduce. Suppose each plant produces 750,000 seeds. Around 75 percent of the seeds take root in the following year.
      1. How many Palmer amaranth plants take root in the following year (year 2)?  Answer: 750,000 x 0.75 = 562,500 plants take root
      2. Assume the measures listed above are taken to control the Palmer amaranth (there is an 88 percent survival rate). How many Palmer amaranth plants will root in the next year (year 3), assuming 75 percent of remaining seeds will take root.  Answer: 562,500 x 0.88 = 495,000 surviving plants; 495,000 x 0.75 = 371,250 plants take root
      3. This year, an increasingly effective herbicide is introduced. Only 20 percent of plants will survive and reproduce. How many plants will take root (still assuming 75 percent)? Answer: 371,250 x 0.20 = 74,250 surviving plants; 74,250 x 0.75 = approximately 55,688 plants take root
    2. Have students make adjustments! How could the Palmer amaranth population be lowered quickly? Which makes a larger difference: adjusting plant survival rate or plant root rate? This scenario and its rates can be altered to best suit needs.

Did you know? (Ag facts)

  • Palmer amaranth grows extremely fast under ideal conditions—as much as 2-3” in one day!
  • This invasive species can also grow very tall. It can reach heights of 6-8’!

Extension Activities (how students can carry this beyond the classroom)

  •  Ask students to create a “WANTED” poster on another invasive species that is affecting local farmers. On the poster, students can include:
  • Have students do further research on herbicide resistance. Ask students to find a particular case of documented herbicide resistance.
    • What caused the resistance?
    • What weeds/invasive species became resistant to the herbicide?
    • Thinking back: Are there ways the resistance could have been prevented?
    • How were crops affected? What actions did farmers have to take?

Suggested Companion Resources (books and websites)



Kaia Johanningmeier        

Organization Affiliation

The University of Iowa

Agriculture Literacy Outcomes

  • Identify non-native or invasive species in the state that impacts the sustainability and/or economic value of natural or agricultural ecosystem.

Iowa Core Standards

  • HS-LS2-2. Use mathematical representations to support and revise explanations based on evidence about factors affecting biodiversity and populations in ecosystems of different scales.
  • HS-ESS3-3. Create a computational simulation to illustrate the relationships among management of natural resources, the sustainability of human populations, and biodiversity.
  • HS-ETS1-2. Design a solution to a complex real-world problem by breaking it down into smaller, more manageable problems that can be solved through engineering.

Creative Commons License

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