Module 7 - Weeds

Welcome to the final module of the short eight week summer semester. This weeks topic is IPM of weeds. Image source: pawpaw67

ANNOUNCEMENTS

INTRODUCTION
The first thing you need to do is think of the term "weed" as a concept and not simply a list of plant species you memorize for their detrimental impact on the landscape. A weed is simply a plant in a location where it is utilizing resources we would prefer be available to other plants. A plant species can be a weed in one location and desirable in another.

Weeds utilize water, sunlight, nutrients, and ecological niches that could be used by crops, plants installed in the ornamental landscape, or native plants in the ecosystem. Consider all the wasted money that goes to weed management that just results from irrigating non-target landscape areas.

A weed could be a dandelion in the garden, a barberry that has escaped cultivation and now is reproducing by seed in a pasture. A common roadside example is Paulonia tomentosa, an introduced tree species that rapidly colonizes road cuts in many parts of the mid-Atlantic United States.

Similar to many of the other horticultural pests we have covered, weeds require a special skill set to manage properly. Their are several landgrant institutions in the United States that offer a Ph.D. in weed science.

LEARNING OBJECTIVES

• Discuss the concept of a "weed"
• List some of the different life cycles of common weeds
• Compare and contrast some different strategies for weed management
• Differentiate between contact and systemic herbicides
• Discuss some of the modes of action of common herbicides
• Discuss how some novel biological control methods work by taking IPM principles into consideration

Dandelion seed ready for dispersal. Dandelions are infamous as prolific seeders and the taproots can make removal difficult. Image Source: D H Wright

TERMS TO KNOW

• site surveys, transect counts
• headers, competitive plantings
• allelopathy, cultivation, solarization
• organic mulch, synthetic mulch, weed barrier
• dandelion knives, weed knife, hula, hoe, briar hook
• flame weeding, hot water treatment, biological weed control
• contact herbicide, systemic herbicide, organic-approved herbicides
  

READING AND MULTIMEDIA ASSIGNMENTS

• Chapter 7. Weeds. pages 297-340, focus on 297-320.
• Watch YouTube video on using Goats as part of an IPM program
• Watch YouTube video on how invasive snail is being used for weed control of lowland rice

Thistle, another common weed, albeit a beautiful one. Image Source: Aunt Owwee

STUDY QUESTIONS (5 points each, answer in complete sentences)

1. Develop your own concept for "weeds" be sure to cover all potential uses of the word.
   
   
2. A key part of IPM, as in the case of insect pests, is that some weeds be tolerated. How does a horticulturalist determine what can be economically tolerated.
   
   
3. A local landscape maintenance contractor tells you (a new business owner) that the best time to control weeds is late spring "when you can see what you are dealing with" support or refute the contractor's statement.
   
   
4. Discuss three different ways that landscapes can be designed to reduce weed competition from the beginning.
   
   
5. Allelopathy is a tool that is being considered more frequently in modern landscape design. Describe allelopathy and list some commercial applications of this natural defense mechanism. You should be able to find one or two research projects using an Internet Search Engine.
   
   
6. Cultivation, either by hand or mechanically can help control weed populations. Mechanical cultivation requires careful attention. Explain some of the considerations that should be made with mechanically cultivating a site for weed control.
   
   
7. Soil solarization is gaining popularity both as a control for weeds and some pathogenic nematodes. Explain what soil solarization is and how it works.
   
   
8. Discuss the variety of organic mulches that are available.
   
   
9. What are the advantages to using organic mulch as compared to synthetic mulches?, are there any disadvantages?
   
   
10. What are some disadvantages of using synthetic mulches.
    
    
11. Once weeds have emerged what are some ways you can limit population growth?
12. How is flaming used to control weeds?
    
    
13. Watch the Youtube video on goat control of weeds again. How does this pest manager use IPM to control target weeds. Be sure to cover the multiple benefits provided by the goats.
    
    
14. Watch the Youtube video on the invasive species of snail now used to control weeds in lowland rice. How did some clever problem solving lead to a potential solution? Innovators with an open mind can often solve problems by using the resources at hand.
    
    
15. What are some other types of biological controls that were covered in your textbook? Provide specific examples.
    
    
16. Sometimes chemical control of weeds using pesticides becomes necessary. Outline fundamental safety precautions that should always be followed when using synthetic herbicides or any chemical for pest control.
    
    
17. Differentiate between the mode of action of a systemic herbicide and a contact herbicide. Give an example of each that is commonly used in the landscape industry.
    
    
18. Discuss some of the modes of action of preemergence herbicides.
    
    
19. Discuss some of the modes of action of postemergence herbicides.
    
    
20. Conduct Internet Research. Develop a list of the top 10 worst landscape weeds for the Western North Carolina Landscape. Be sure to cite your references.

Out of control weed population in an abandoned lot near a highway. Image Source: Editor B.

EXTRA CREDIT (+5 possible)
Roundup is one of the most popular herbicides in the landscape industry. Explain the mode of action in detail. What does roundup-ready mean for corn and soybeans? How exactly are roundup-ready corn and soybeans produced?