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Milkweed Check-Up


Here's an activity to accompany the information on the common milkweed, biomonitoring and Air Quality Days on EEK!

Students will 1) locate and identify milkweed, 2) observe signs of ozone plant damage, 3) determine the severity of ozone damage to individual plants and plant communities.

Students conduct observations of milkweed leaves and identify signs of ozone damage.


Did you know that plants and animals can give us clues about pollution in our air, land, and water, before humans even notice that something is wrong? Even lichens and birds can tell us about air quality. Biomonitoring is the term scientists use to describe this use of plants, animals, or entire ecosystems to tell if our environment is polluted. These techniques have been used by biologists and scientists to give us information about our surroundings for a long time.

In Wisconsin, common milkweed is a good plant to study for signs of pollution because it is affected by ozone and it grows in a lot of areas. Your students can be environmental doctors and conduct a simple milkweed check-up for ozone damage. Ozone injury on milkweed can be seen on the leaves. This injury is unique and is pretty easy to identify. As plant doctors, students can look for these symptoms: sharply defined, small dot-like lesions, called stipples, on the top (upper surface) of the leaves. These markings appear only on the top of the leaf and are black to dark purple. If the ozone effects are severe you'll see a large dark area on the upper leaf surface as the markings blend together.

Ozone injury can look different on leaves of different ages. Minor ozone injury on young leaves can be found on the tip of the leaf. It is found in the center of fully grown leaves and at the base of older leaves. Leaves that are exposed to lots of ozone may show injury symptoms all over the upper leaf surface. You and your students can view a slide show of ozone and other damage to milkweed leaves to help you in your studies.


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Wisconsin's Model Academic Standards:

  • Information and Technology Literacy B.8.4
  • Language Arts D.8.1
  • Mathematics A.8.6 D.8.1 D.8.2 D.8.3 D.8.4 E.8.2 E.8.6
  • Science A.8.3 C.8.2 C.8.6 D.8.8 D.8.9 E.8.3 E.8.4 F.8.9 F.8.10 G.8.3
  • Social Studies D.8.11


1. Select a Study Area.
Select a study area in late August or September that has these characteristics:

  • Plants are at least 50 feet from the road (to avoid the effects of vehicle exhaust, road salts, and road side mowing). Abandoned fields, remote unmowed areas in parks or prairies are ideal sites.

  • Have students select a study area that has at least 20 milkweed stems that are somewhat close together.

  • Remember, if the area is on private land, get permission from the landowner to conduct research at that location.

2. Have students select milkweed plants to conduct the check-up.

  • a. Have students choose 10 stems at random for the study. Each plant must have a stem with 10 or more leaves on it. Have students avoid plants that are diseased or have insect chewing marks on them.

  • b. Have students draw a map showing the location of the study area. Show features near the site like roads, trails, signs and buildings that would allow another person to easily find the site.

  • c. Have students use the chart below to record their findings.
  • 3. Have students conduct the check up.

  • a. Students should select their first milkweed stem and measure and record the height of the stem from the base to the top. Have students use inches for their measurement and record this on the chart.[stiples - leaf injury]

  • b. Students should count and record the number of leaves showing ozone injury on the plant (see the picture to identify leaf injury).

  • c. Have students estimate the percentage of leaf area injured using the following code:

    Code % of leaf area injured
    0 no visible signs of injury
    1very light to some (1-15%)
    2moderate to moderately heavy (16-50%)
    3heavy (more than 50%)

  • d. Have students count and record the number of leaves showing ozone injury on the plant.
  • They should also record the total number of leaves on the plant. Have them evaluate only mature leaves that measure 2-4 inches in length. Students should then determine the percentage of injured leaves per plant using the guide above. Have them complete all 10 plant check-ups.

    Plant Number Plant Height Total # Leaves # Injured Leaves % Injured Leaves on Plant % Leaf Area Injured

    1. What level of injury did you find?

    2. If you found no ozone injury, what might this mean? How can you verify your results?

    3. What is a bioindicator? How can using milkweed and other plants as bioindicators help us keep the air clean?

    4. What are the advantages or disadvantages to using biomonitoring projects?

    5. Compare your results with a local air quality monitoring agency. Are they similar? Different? What might cause the results to be different?

    Students can collect 10 injured leaf samples and press them for a field notebook.

    In the field students can place leaf samples in a book to keep the leaves from curing and drying too fast. A simple press can be made by placing the leaves between sheets of newspaper and inserting the newspaper between two sheets of cardboard. Then sandwich this between two pieces of wood or hardboard and close tightly using rope or weights. The press should be left in a well ventilated room to enable the leaves to dry properly. Drying will take 7-10 days. When the leaf is dry and brittle, have students carefully tape the leaf to a 8.5 x 11 sheet of paper and be sure to keep the label with each sample. Each leaf should be clearly marked with the plant number and percentage of ozone injury.

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