Epidemiology
What is the disease progress curve? And what are two ways to measure it?
Change in disease variable over time.
-Disease Incidence
-Disease severity
What disease principle does this match to?
1. Reduce or eliminate a pathogen that already exists at the production site
2. Reduce disease by making the environment less conducive, even though the host and pathogen are present
3. Prevent a pathogen from entering the growing region or production site
1. Eradication
2. Avoidance
3. Exclusion
Define the four modes of action of biological agents
1. Predation/Parasitism (biocontrol agent feeds on the target organism).
2. Competition (biocontrol agent outcompetes the target organism for resources).
3. Antibiosis (biocontrol agent produce substance that inhibits the target organism).
4. Indirect effects (biocontrol agents have an effect on another organism or the environment which controls the target organism).
What is the difference between chemical products that end in -cides vs. -stats
-cides: irreversible inhibition of the pathogen
-stats: reversible inhibition of the pathogen
What is economic injury level?
Point at which loss from damage exceeds cost of control
Differentiate between disease severity and Incidence
Disease Incidence is a binary(qualitative) measure and is usually expressed as a percentage (%).
Disease severity is a quantitative or semiquantitative measure that involves disease rating (%leaf area infected, lesion size, disease scale).
Reducing the initial inoculum of the pathogen will be most efficient for what type of epidemic? Monocyclic or Polycyclic?
What strategy works for the other?
Monocyclic (this is because both initial inoculum and rate of disease spread have the same multiplication factor).
For Polycyclic- Reducing the rate of disease spread is most efficient.
A cellulolytic fungus used as a biocontrol agent that prevents an oomycete from producing sporangia, thereby reducing the disease severity caused by the pathogen, uses what kind of mode of action?
Antibiosis
The fungus produces cellulase that prevents the oomycete fungus from reproducing and disseminating.
What are the systemic types of active ingredient movement in plant tissues?
- Local (across waxy surface)
- Translaminar (through leaf lamina)
- Apoplastic (movement in water, between cells and through xylem)
- Symplastic (movemment cell to cell and in phloem)
- Amphimobile (both up and downward)
What is IPM?
Integrates cultural, biological, and chemical control
- manage disease, pest, and weed problems
- achieve control with lowest possible inputs
- achieve control with least possible impact on environment
List 4 factors you need to know when forecasting a disease.
-Biology of the pathogen.
-Favorable weather conditions for the disease
-Amount of inoculum set as threshold for detection.
-Pattern of disease progress.
What principles do the following cultural methods follow?
1. Regulatory control and Inspection of pathogen-free seeds.
2. Row spacing in the field and use of raised beds.
3. Early planting to favor the host over the pathogen.
4. Removal of sclerotia-infested soil in the field.
1. Exclusion
2. Avoidance
3. Avoidance
4. Eradication
The pathogen can be native or non-native, but the natural enemies are native, but in few numbers.
The natural enemies are then grown elsewhere and introduced into the system in small numbers.
What kind of biocontrol application is this?
Inoculative Augmentative biocontrol.
What are the types of chemicals?
- Inorganic (copper, sulfur, carbonate compounds, phosphate)
- Organic (contact & systemic)
- Antibiotics
- Soil Fumigants
What are some examples of IPM?
- Crop location
- Crop rotation
- Cultivar selection & seed source
- Irrigation (type, timing, frequency)
- Bed preparation
- Sanitation
- Chemical application
- Planning and harvest time
- Forecasting and monitoring
What is inoculum density and inoculum potential?
Which is difficult to measure and requires a bioassay?
Inoculum density- number of propagules per unit weight of volume (easy to measure).
Inoculum potential- number of propagules (quantity) and proportion of inoculum (quality) that can infect.
-Inoculum potential requires you to perform a bioassay.
Crop rotation with alternating crops will not be most effective for which of these?
1. Airborne spores vs. Soil-borne propagules
2. Soil survivors vs. Soil inhabitants
1. Air-borne pathogens
2. Soil survivors (they are in the dormant stage in the soil).
Pepper leaves sprayed with Pseudozyma churashimaensis strain RGJ1 showed a 60% reduction in disease severity from Xanthomonas axonopodis infection.
In culture, the RGJ1 did not inhibit X. axonopodis growth.
Disease reduction could be observed whether RGJ1 was applied as a foliar spray or root drench, after infiltrating the pathogen directly into leaf tissue.
What is the mode of action for this biocontrol?
Induced resistance
What are some methods of managing resistance?
- Reduce number of applications
- Use early, before log phase
- Alternate chemistries
- Mix chemistries
- Sub or combine with non-chemical methods
What is the use of action thresholds in IPM chemical controls
- Applications made relying on monitoring and knowledge base
- Importance of disease forecasting systems
Monocyclic vs Polycyclic
1. Rust disease will follow what type of epidemic model?
2. Powdery mildew will follow what type of epidemic model?
3. Disease caused by root knot nematode will follow which epidemic model?
Monocyclic- One infection cycle per growing season (saturation curve).
Polycyclic- multiple cycles per growing season (Sigmoid curve).
1. Rust - Polycyclic
2. Powdery mildew- Polycyclic
3. RKN- Monocyclic
What principle(s) can be used to disrupt the following part of the disease cycle:
1. Inoculation, 2. Attachment, 3. Penetration,
4. Infection, 5. Survival
1.Inoculation (Avoidance)
2. Attachment (Protection and Avoidance)
3. Penetration (Avoidance, Protection and Resistance)
4. Infection (Resistance)
5. Survival (Eradication)
List 3 considerations of a good biocontrol agent.
List 3 limitations in using biocontrol agents for disease control.
Considerations:
Easy to grow, Easy to store, specific to the target organism, competes well with other organisms.
Limitations:
Lack of specificity, poorly adapted to the site of use, variability in efficacy.
How does pesticide resistance work?
After pesticide application, targeted susceptible pathogen population will significantly reduce in number, and resistant populations will persist.
As pathogens reproduce, the previously underrepresented resistant pathogen now has less competition, and is able to become the dominant pathogen population
What are some advantages and drawbacks to IPM?
Advantages:
- reduce costs of inputs
- reduce worker exposure risk
- encourage more sustainable practices
Disadvantages:
- requires extensive knowledge of pathogen biology and epidemiology
- may involve increased labor
- effects on chemical control