Using Fusarium Wilt to Control Drug Crops
This exercise has three parts:
- To prepare for the discussion, have students read about Fusarium wilt in a commercial crop. This will help them understand more about the disease and what management approaches are available. Also have students read articles from the New York Times on the use of Fusarium wilt to control marijuana in Florida and the use of both Fusarium wilt and glyphosate to control coca in Colombia and Peru. Have students critically analyze the articles for accuracy.
- Next, have a group discussion to help students focus on accurate and inaccurate information and to help them develop an educated opinion on the use of glyphosate versus Fusarium wilt for control of drug crops.
- Ask each student to write a short paper expressing his or her opinion on which tool to use to destroy drug crops. Students should base their opinions on what they have learned about glyphosate and Fusarium wilt.
Part 1 - Writing Assignment to Prepare for Group Discussion
Fusarium wilt is caused by the fungal species Fusarium oxysporum. There are many subspecies of this fungus that are host specific. This means that they look identical but vary in what plants they can infect. These subspecies are designated by the Latin phrase forma specialis (f. sp.), which means “special form.” The plural of this phrase is formae speciales. For example, Fusarium wilt of tomato is caused by Fusarium oxysporum f. sp. lycopersici.
This fungus infects plants primarily through the roots and then becomes a vascular wilt pathogen, which means it invades the xylem and prevents uptake of water and minerals. Note that the fungus produces three kinds of spores: macroconidia for infection of roots, microconidia to aid in distribution of the fungus in the xylem, and thick-walled chlamydospores for survival in the soil.
Here are two possible sources to use:
- APS Plant Disease Lesson: Fusarium Wilt of Watermelon
- Fusarium wilt sections of various vegetable disease compendia published by APS—for example, Fusarium wilt of tomato in the Compendium of Tomato Diseases.
Directions to Students:
You will use this assignment for the group discussion, and then turn it in. Keep an extra copy for yourself for use in writing the next paper on using Fusarium wilt to control drug crops.
For the Fusarium wilt disease you have been given to study, answer the following questions:
- Host plant (English and scientific names)
- Pathogen name: Fusarium oxysporum f. sp. ______________________
- Symptoms and signs (What does it do to the plant?)
- Means of dissemination (dispersal) and survival (Do you see references to macroconidia, microconidia, or chlamydospores or to water, air, soil?)
- Management: Are any of these methods used for the Fusarium wilt you read about?
- Cultural practices:
Resistant plants (cultivars) available?Chemical (fungicide) treatments recommended? If not, why not? (Hint: Think about how this pathogen enters the plant and where it is located in the plant.)Any other interesting or important information to note?
- Crop rotation?
- Modification of soil pH, fertilizers used?
Part 2—Group discussion of the use of Fusarium wilt for biological control of coca (source of cocaine) in Colombia and Peru and biological control of marijuana in Florida
- Read the following articles from the New York Times. Evaluate each article for accuracy, given what you know about Fusarium wilt, the fungal pathogen Fusarium oxysporum, and the herbicide glyphosate. Note any statements in the article that you doubt.
- Fusarium wilt to control marijuana: “A Fungus to Kill Marijuana Has Environmentalists Wary,” July 27, 1999
- Fusarium wilt to control coca: “Fungus Considered as a Tool to Kill Coca in Colombia,” July 6, 2000
- Herbicide (weed killer) glyphosate to control coca: “No Crops Spared in Colombia Coca War,” January 31, 2001
- Download a fact sheet on glyphosate from the Pesticide Action Network UK
- Answer these questions to prepare for discussing the articles:
- How would you establish the fungus in a coca-growing area to effectively kill the plants?
- What would be the advantages of using Fusarium wilt for biological control compared to herbicides (e.g., glyphosate)? (Consider ethical, biological, and environmental aspects.)
- What would be the disadvantages of using Fusarium wilt compared to herbicides?
- Discuss the articles with your group in class.
- Students can likely find the New York Times articles themselves. Most university libraries offer registered students access to archived articles. Otherwise, the articles can be posted on a class website or printed and distributed in class. Students are usually quite amazed to find inaccurate statements in the New York Times.
- Remind students about the significance of LD50 when discussing glyphosate.
Part 3 - Writing Assignment
Write an essay of 300–400 words (more if absolutely necessary). The essay must be typed. Answer these questions in the essay (don’t just answer the questions):
- How could you use Fusarium oxysporum (Fusarium wilt) to kill a drug crop such as coca or marijuana (i.e., how would you get the fungus to the crop for infection)?
- What are some advantages and disadvantages of using Fusarium wilt, rather than herbicides (weed killers)?
- What is your opinion about using Fusarium wilt for killing drug crops? Is this biological control or bioterrorism?
Note: You may have the opinion that Fusarium wilt, herbicide, or neither should be used. Justify your opinion with scientific facts about both control options.