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Question 1

Define ‘pest’.

Answer 1

Any organism causing harm or damage to people or their animals, crops, or possessions.

Question 2

Which causes more production losses worldwide:

1. Weeds
2. Pathogens and nematodes
3. Insects and mites

Answer 2

3. Insects and mites

Question 3

True or False?

Worldwide crop losses would increase from 40 to 50% without chemical controls.

Answer 3

False.

Worldwide crop losses would increase more than that, from 40% to 70% (Oerke et al. 1994)

Oerke, E.C., Dehne, H.W., Schonbech, F. and Weber, A. 1994. Crop Production and Protection: Estimated Losses in Major Food and Cash Crops. Elsevier, Amsterdam.

Question 4

True or False?

Pesticide use could be reduced by 30% without reducing crop yields or substantially reducing cosmetic standards.

Answer 4

False.

Pesticide use could be reduced by 50-60% without reducing crop yields or substantially reducing cosmetic standards (Peshin & Pimentel, 2014).

Peshin, R., Pimentel, D., 2014. Integrated Pest Management: Experiences with Implementation. Volume 4. Springer, New York.

Question 5

When are decisions about plant protection made?

Answer 5

Constantly.

Even from the very beginning of the planning phase, a producer should know the condition of their soil (for example) and the pest load it carries in order to make decisions about which crops and varieties to grow.

Question 6

Define ‘Integrated Pest Management (IPM)’

Answer 6

Gentz et al. (2010) summarised Integrated Pest Management (IPM) excellently, stating that:

“[IPM] combines chemical, biological, and cultural control [methods] to provide targeted and efficient pest management solutions that can be tailored to specific climates and habitats in order to maximize a program’s efficacy.”

In other words, IPM represents a combined approach to managing agricultural pests and diseases, where reliance isn’t on any one particular strategy, but on the effect of multiple strategies working together.

Question 7

What are the (5) pillars (controls) of IPM?

Answer 7

• Biological
• Behavioral
• Chemical
• Cultural
• Genetics

Question 8

What are the foundations of IPM, without which the control strategies would be useless.

Answer 8

• Taxonomy (knowing which pest it is)
• Biology (how they live and die)
• Ecology (their interactions with the environment)
• Thresholds (at what point (size) their population requires management to prevent economic losses)
• Sampling (to monitor population density)
• Models (to estimate changes in population density based on certain conditions (temperature, humidity, light, population size, competition, crop maturity, etc).

Question 9

There are 5 main aims of IPM. Explain them.

Answer 9

1. Understand the pest biology and its status in the target system
   
   • Which species are (or might be) present
   • At what density
   • What factors affect their population density
   • What damage do they cause
2. Understand the economics of pest damage
   
   • How does their presence affect yield and quality
   • What are the financial consequences of their affect?
   • How much will it cost to control
   • What yield/quality gain can be achieved by control
3. Understand the ecological and sociological impacts of pest control strategies
   
   • Effects on natural predators
   • Effects on non-target organisms
   • Effects on surrounding ecosystems
   • Effects on human health and safety
   • Customer/consumer confidence
4. Avoid or prevent pest problems in the first place (i.e. before they become a problem)
5. Careful selection of control measures
   
   • Preferential use of least-toxic means of pest supression
   • Preferential use of methods that are least disruptive to natural enemies and non-target organisms
   • Use of methods that are most likely to be permanent
   • Use of methods that are cost effect in the short and long term.

Question 10

What are the (6) main steps in developing an IPM program?

Answer 10

1. Diagnosis (Identify the cause(s) of damage)

• species
• spatial distribution
• population density

2. Thoroughly understand the pest’s biology and ecology

• life cycle
• interactions with other pests, predators, and organisms in the target system (incl. plants)
• seasonal activity
• dormancy
• method of dispersal
• how they’re affected by environmental conditions (temp, humidity, light, wind, etc)
• source of nutrients

3. Set action thresholds (at what level of infestation you’ll take action)

• How does their presence affect yield and quality
• What are the financial consequences of their affect?
• How much will it cost to control
• What yield/quality gain can be achieved by control
• Population density < EIL, cost > benefit
  Population density > EIL, benefit > cost

4. Formulate control strategies

• Target weak links in the biology/ecology
• If possible, change the system to avoid or prevent losses by pests
• Consider social and environmental impacts (externalities) and any other adverse (e.g. health) affects.
• Preferential use of least-toxic strategies
• Combine strategies if cost-effective to do so

5. Utilise IPM practices

6. Evaluate outcomes

• Economic returns
• Environmental impact
• Social consequences (e.g. customer perception)

Question 11

Before any pest control can occur, one must ask the question whether there is a real pest problem or a perceived pest problem. Why is this?

Answer 11

Because many symptoms can appear as pest damage, but are actually caused by abiotic or other biotic stresses such as:

• nutrient deficiency/toxicity
• frost
• waterlogging or water unavailability
• wind
• salinity
• weed competition
• birds
• herbicides

Question 12

Is crop damage influenced by the stage the plant is at in its lifecycle?

Answer 12

Yes.

Younger plants are generally more susceptible.

The economic consequences are also going to be different depending on the life stage; e.g. if a cereal becomes infected by a pest at the late heading stage, it might not be that big of a problem if the head is already mostly formed.

Question 13

How does the season affect the interaction between pest organisms and plants?

Answer 13

• Temperature
• Moisture availability
• Wind (air)
• Light
• Day length

Question 14

Describe the disease triangle

Answer 14

A graphical representation of the interaction between a pathogen or pest, it’s host, and the environment.

Question 15

Which pest is most likely to cause the least symptoms and why?

1. Bacteria
2. Viruses
3. Necrotrophic fungi
4. Biotrophic fungi

Answer 15

4. Biotrophic fungi

Relies on the host being alive and unaware of its presence (to avoid initiating a defense response)

Question 16

How do insects infect/enter plant hosts?

Answer 16

Entry is mechanical (chewing, piercing, sucking) or enzymatic (breaking down the cell wall, sucking out the juice).

Question 17

How do bacteria infect/enter plant hosts?

Answer 17

Infect through natural openings (e.g. stomata) or wounds

Question 18

What symptoms would you expect from a bacterial infection?

Answer 18

• Necrosis
• Wilting
• Rotting of fruits/tubers
• Gall formation

Question 19

True or False?

Bacteria are mostly necrotrophs

Answer 19

True

Question 20

True or False?

Bacteria are mostly biotrophs

Answer 20

False.

(Bacteria are mostly necrotrophic)

Question 21

How do viruses infect/enter plant hosts?

Answer 21

Infect through wounds or vectors but become systemic (i.e. spread throughout the plant)

Question 22

True or False?

Viruses are mostly necrotrophic

Answer 22

False.

(They’re biotrophic - they need a host to replicate, so they don’t want to kill the tissue, and hence cause less damage)

Question 23

True or False?

Fungi are mostly biotrophs

Answer 23

Fungi can be either biotrophic, necrotrophic, or hemibiotrophic, where they start out biotrophic, then become necrotrophic.

Question 24

How do nematodes infect/enter plant hosts?

Answer 24

Entry is mechanical (stylet)

Question 25

What symptoms would you expect from a viral infection?

Answer 25

• Dwarfing (affecting hormones)
• Leaf necrosis (ring spot)
• Mosaic
• Leaf roll
• Yellow stripe

Question 26

What symptoms would you expect from a nematode infestation?

Answer 26

• Growth reduction
• Wilting
• Mineral deficiencies
• Decreased winter-hardiness

Because they’re getting into the root, it changes the root function and makes it difficult for the plant to take up water and nutrients. Mineral deficiencies are often the most obvious symptoms.

Question 27

Explain some features of necrotrophic fungi

Answer 27

• Kill cell before invasion
  
  • toxins, cell wall degradation
• Usually grows through tissue without any major problems
• Usually have a wide host range (e.g. Botrytis cinerea grows on > 3000 different species)

Question 28

How do fungi and oomycetes infect/enter plant hosts?

Answer 28

Entry is mechanical (penetration and formation of haustoria) or with toxins/enzymes.

Question 29

Explain some features of biotrophic fungi

Answer 29

• “Sneak in” without causing major damage in order to avoid being recognised by the plant and initiating a defense response.
  
  • Can require enzymes such as pectinase and glucanase
• Obtain nutrients from the apoplast (intercellular space) or by forming haustoria (pushing against the plant’s plasma membrane and forming a structure with a large surface area inside the plant’s cell (think of pushing a hand into a balloon through the side)).
• Very narrow host range (e.g. Puccinia graminis, the fungi that causes leaf rust, only grows on some cultivars of wheat)

Question 30

Define ‘pathogenicity’.

Answer 30

The ability of a pest to cause disease on a particular host

Question 31

Define ‘virulence’.

Answer 31

The degree of damage caused by the pest to the host.

Question 32

Why is the distinction between pathogenicity and virulence important?

Answer 32

Because a pathogen might have the ability to cause disease (i.e. have a high level of pathogenicity), but may cause minimal damage (i.e. have a low virulence), making it not worth worrying about.