Module 5 - Plant Diseases

A tree with root rot has fallen over. The increased soil moisture resulting from a Beaver dam facilitated disease development by impacting by altering the environment component of the disease triangle. These leaves an opening for plant succession, but in the landscape this is undesirable and could lead to increased soil erosion.

ANNOUNCEMENTS

INTRODUCTION
Plant disease causing organisms are present in every landscape. However, by managing certain factors a horticulturalist can control the level of disease in the landscape. Disease can be reduced by using resistant plants, starting with the highest quality planting material, using appropriate plant health-based design principles, monitoring irrigation, applying appropriate nutrition, using proper pruning (as seen in previous modules), and practicing good sanitation.

Plant Pathology is a discipline unto itself. This module can only be considered a cursory review. Additional training is available in many extension courses and through University courses. This module will use Dutch Elm Disease and information provided by the American Phytopathological society to review some common themes in the spread of plant diseases.

LEARNING OBJECTIVES

• Discuss the various types of disease causing organisms
• Differentiate between hallmark disease symptoms and their associated pathogens
• Explain disease management strategies commonly used in horticulture
• Familiarize yourself with some disease cycles

Occasionally, virus infections can yield interesting ornamental patterns. The color breaking pattern in the tulip (right) is the result of a virus. Some modern cultivars with consistent breaking patterns are not result of infection, but rather breeding. Although, colorful the virus infection does result in a loss of vigor. Image Source: RcktMsnIL

TERMS TO KNOW

• fungi, bacteria, viruses, phytoplasmas
• resistant plants
• sanitation
• soil sterilization
• biological control
• beneficial microorganisms
• fungicides and bacteriacides
• the disease triangle
  

READING AND MULTIMEDIA ASSIGNMENTS

• Read Textbook pages 209-271. Focus on 209-222
• Dutch Elm Disease Lesson ALL MENU ITEMS
• Watch YouTube Video on Diseases in the Garden
  

In addition to the direct damage from feeding aphids also transmit viruses, although this is a much bigger problem in food crops than in the landscape. Image Source: Jeanette H.
STUDY QUESTIONS (Answer each question below in complete sentences, 5 pts each).

1. Briefly describe the 4 classes of plant pathogens as discussed in your textbook.
   
   
2. Conduct internet research. (Hint: you may want to start with the American Phytopathological Society link below). Come up with an estimate of the economic losses due to plant disease that occur on an annual basis globally.
   
   
3. How do you treat a landscape plant that has become infected with a virus?
   
   
4. Describe the plant disease triangle.
   
   
5. For the plant disease triangle list 4 things that a horticulturalist can do for each of the 3 corner concepts that will limit plant disease development in the designed landscape.
   
   
6. How can a landscape designer help improve plant health by optimizing planting site and design?
   
   
7. Describe proper sanitation. Thinking holistically how do you manage sanitation while also promoting healthy populations of biocontrols (see figure 4.5 in your text as an example). Can you see how developing a pest management strategy can quickly become complicated? Again we are trying to control many small practices in order to avoid a major intervention such as a broad spectrum pesticide.
   
   
8. Discuss the role of irrigation in the development of soil borne root diseases. Briefly discuss how irrigation can be scheduled throughout the year to help limit such problems.
   
   
9. Where should irrigation microsprinklers be placed for a mature Red Maple in the a Western North Carolina residential landscape?
   
   
10. Briefly describe how to treat 'shot hole' on a Purpleleaf plum in a client's landscape.
    
    
11. Differentiate between synthetic fungicide, botanical fungicide, and inorganic fungicide.
    
    
12. Differentiate between the symptoms of scabs, rusts, viruses, and bacterial blights. Obviously your answer needs to be very generalized.
    
    
13. Choose one disease of interest to you covered in your textbook and describe its lifecyle.
    
    
14. How was Dutch Elm Disease introduced to trees in the United States?
    
    
15. Discuss the factors that contributed to the rapid spread of Dutch Elm Disease to the large population of Ulmus americana in the United States, frame your discussion in terms of the disease triangle.
    
    
16. Describe the life cycle of the two pathogens known to be responsible for Dutch Elm Disease.
    
    
17. Describe the symptoms of Dutch Elm Disease.
    
    
18. Choose one of the three control strategies for Ductch Elm Disease and discuss it in detail.
    
    
19. What lessons from the Dutch Elm Disease epidemic can be utilized to reduce the potential of plant disease in any ornamental landscape?
    
    
20. Give two examples of virus infections that result in enhanced ornamental characteristics for their plant hosts.
    

EXTRA CREDIT (+3) briefly summarize the approach and results to date of one of the several plant breeding programs around the U.S. specifically focused on reducing the impact of Dutch Elm disease.

OTHER RESOURCES
American Phytopathological Society

American Elm tree in decline from Dutch Elm Disease. Image Source: Drab Makyo