Grade Level: 6th to 9th; Type: Biochemistry
Allelopathic substances work like herbicides, preventing the germination and growth of the seedlings of competing plant species. The research aspect of this science fair project is to compare the natural allelopathic chemical produced by the Black Walnut tree to that of a commercial herbicide in stopping the growth of a shrub.
- What is allelopathy and juglone?
- How will the honeysuckle shrub be affected by the application of juglone solution compared to that of a commercial herbicide?
- How long will it take for a shrub sprayed with juglone solution to die?
- How long will it take for a shrub sprayed with a commercial herbicide to die?
- Which plant died first?
- Based on the experimental results should juglone be considered as a natural herbicide?
- Honeysuckle shrubs (or seeds)
- Black walnut hulls (or leaves, bark, or roots), which can be obtained from www.scienceinabag.com/AllelopathyPage.html
- Name brand commercial weed & grass herbicide Ϯ
- Three plastic cups or flower pots
- Plant spray bottle
- Large cooking pot
- Marking pen
- Potting soil
Ϯ Purchase only a commercial herbicide designated as being “systemic” if at all possible.
- Gather three young honeysuckle shrub plants and place each in separate flower pots or plastic cups.
- Label the three flower pots or plastic cups, “natural herbicide,” “commercial herbicide,” and “control.”
- Place all of the plants in an area where they will receive the same amount of sunlight.
- Place two or three Black Walnut hulls (or 20 leaves) in a pot and fill the pot half full with distilled water.
- Bring the hull-water mixture to a boil. Boil the hulls (or leaves) and water for 10 minutes using the stopwatch to keep track of time.
- After 10 minutes, use a large spoon to remove the hulls from the water.
- Continue to boil the now extracted juglone solution for 20 minutes.
- After 20 minutes, allow the liquid to cool completely. Once the liquid has cooled, pour it into a flower spray bottle.
- Follow the directions written on the commercial herbicide label for the amount of herbicide that should be applied to the honeysuckle shrub.
- Apply the same amount of juglone solution to the honeysuckle shrub labeled “natural herbicide” as was applied to the “commercial herbicide” plant.
- Do not apply any substance to the plant labeled “control.”
- Observe the plants over several days recording any changes seen. Write all of the observations in a table.
- Use phrases like “no visible change,” “change in leaf color,” “withering of steam,” “stunting of growth,” wilting of plant,” etc. when describing the plants’ appearance over time.
- The data in the table can be visually displayed by plotting a bar graph of natural herbicide vs. commercial herbicide eradication time on graph paper or a computer equipped with Excel, by listing the number of days to the shrub’s death along the vertical axis verses the names of the two herbicides along the horizontal axis.
Terms/Concepts: Allelopathy, Juglone, allelopathic effect, autotoxicity, herbicide, walnut toxicity, Black Walnut Tree, juglone toxicity, Honeysuckle shrub; why might it be more desirable to use allelopathic substances as alternatives to the use of traditional commercially produced chemical herbicides?
- World Food and You, by Nan Unklesbay, pp. 362 (CRC Publishing, 1992).
- Allelopathy in Sustainable Agriculture and Forestry, by Rensen Zeng, Azim U. Mallik, and Shiming Luo, pp. 305 ( Springer-Verlag New York, LLC, 2008).