Stop That Weed!

Overview: This exercise will create an awareness of the methods for controlling exotic species.

Audience: This activity is designed for elementary school students in grades 2-5.

Background: When exotic weeds spread into natural areas, they can crowd out native plants, changing the structure and function of the entire ecosystem. Fighting the spread of invasive weeds often involves the use of multiple control tactics. Herbicides can be effective but expensive and may have harmful effects on other species. Mechanical removal of the weeds by pulling, tilling, mowing, burning, or grazing can help to reduce their spread but usually will not eradicate the plants completely. Biological control agents, such as insects that feed on the plants, can be effective but may take time to establish. When weeds have been reduced, the chances of re-invasion can be minimized by seeding with desirable native plants that are capable of competing with the exotic species. [The ESCAPE web site (http://www.unk.edu/escape) provides additional information on exotic species, an overview of basic ecological concepts, a discussion of the ethics of weed control, and a glossary.]

Time Requirements: This activity can be completed in a 45-minute period.

Objectives: After completing this exercise, students will be able to:
1. List some ways that weeds can be controlled.
2. Describe how weeds compete with other plants.

National Science Education Standards:

• Unifying Concepts and Processes
  • Systems, order, and organization
• Life Science
  • Organisms and their environments
  • Interdependence of organisms
• Science in Personal and Social Perspectives
  • Natural resources
  • Environmental quality

Setting: This activity may be conducted in an outdoor area, such as a park or playground, or in a gymnasium.

Materials:

• Name tags reading "Weed", "Flower", "Herbicide", "Weed-Eater", and "Mower". There should be at least one name tag per student and at least 5 copies of each tag.
• Blind-folds (enough for all the "Weeds" and "Flowers" combined)
• Whistle

Procedure:
1. Ask students, "Have you ever seen a place that was taken over by weeds? Did you ever wonder how those weeds managed to do that and what could be done about it?" Elicit students' ideas about how weeds become numerous. Ask, "What do you think happens to the other plants when weeds take over?" Discuss the possible effects of a weed invasion. For younger students, it may help to relate the topic to their experiences in helping to weed a vegetable or flower garden.

2. Introduce the idea of competition (when living things need the same resources, such as light, space, and water). The students may play "Musical Chairs" to re-inforce the concept of having too many individuals who want the same space.

3. Tell students that since we have come up with some reasons that we don't want weeds to invade and take over, it's time to think about what we can do to fight them. Play one of the following games:

• Game 1:
  • Start with 3 times as many "Weed" and "Flower" name tags as control ("Herbicide", "Weed-Eater", and "Mower") tags. Explain that "Weed-Eater" tags represent insects that feed on the weeds but do not eat flowers.
  • Lay the name tags upside down and allow each student to pick one.
  • Blind-fold the students with the "Weed" tags. These will stand near one another in the center of the game area. The other students will be dispersed within a small distance around the "Weeds".
  • The blind-folded students try to touch or grab or hold the other students in the group. The other students can clap and make noise to confuse the blind-folded weeds as well as to get attention.
  • If a weed touches a student with a "Flower" tag, the flower becomes a weed and is also blind-folded. If a weed touches any control student, the weed is out of the game.
  • The game continues until all weeds are out of the game.
  • Change the number of students in each group to see how the outcome is affected.
    
• Game 2:
  • Start with 3 times as many "Weed" and "Flower" name tags as control ("Herbicide", "Weed-Eater", and "Mower") tags. Explain that "Weed-Eater" tags represent insects that feed on the weeds but do not eat flowers.
  • Lay the name tags upside down and allow each student to pick one.
  • The students form a circle. Choose one student with a "Weed" tag to come out of the circle and run around it
  • At some random time, blow the whistle. The "Weed" should immediately get into the circle by replacing another student.
  • Check the name tag of the person that was replaced by the weed.
  • If the replaced person is a "Flower", the weed gets into the circle and the game continues with the flower running around the circle until the whistle is blown.
  • If the replaced person is a control, the weed is not allowed to enter the circle and should stand out. He or she is considered to be "weeded out". The teacher picks out another weed or flower to run around the circle.
  • The game ends when there are no more seeds or thistles in the circle.
  • Try changing the number of control name tags to see how the outcome of the game is changed.
    

Closure: Gather the students and discuss the activity with them. Students may also write about how weeds affect other plants and how can be controlled.