W4, IPM; Integration, economics, pest forecasting Flashcards
Explain at least 3 ways that IPM could be used to improve pest management in various production systems (e.g. citrus, greenhouse tomatoes, etc).
- ↓ rate of resistance buildup
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Protection of biological control agents
- Prevention/control of secondary pests and pest resurgences
- Unforseen problems
- Integration provides better control
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↓ rate of pesticide resistance buildup
- = ↑ sustainability
- diamondback moth shows resistance to pretty much all insecticides
- powdery mildew resistance to benzimidazoles occurred only 1 year after introduction
- not only good for farmers, also good for the people developing the chemicals - it takes a lot of time and costs a lot of money to develop, so being able to get a decent lifespan out of a new product so they can make a profit is obviously a priority.
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Protection of biological control agents
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Prevention/control of secondary pests
- By applying chemical controls, natural enemies/pradators are removed too, and in some cases, such as with two-spotted spider mites, the pest is able to recover far quicker than the predator, meaning you end up with an outbreak of a secondary pest.
- predatory mites are more sensitive to miticides than the pest.
- By applying chemical controls, natural enemies/pradators are removed too, and in some cases, such as with two-spotted spider mites, the pest is able to recover far quicker than the predator, meaning you end up with an outbreak of a secondary pest.
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Pest resurgence
- Similar to the effect of secondary pests
- By applying pesticides, there’ll be a decrease in the pest population, but there’ll also be a decrease in the predator population, which allows the pest to recover, often to numbers greater than they were originally, because the predatory control pressure on them is reduced.
- Because pest/predator cycles are delayed slightly, it might be too late for the cash crop by the time the predator population increases to the pont where it can control the pest (assuming there wasn’t another application of pesticides that started the cycle over again).
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Prevention/control of secondary pests
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Unforseen problems
- We never really know what the full consequences of control strategies are going to be, and sometimes, especially with chemical controls, they can be problematic.
- for example, fungicide sprays for late blight fungus were associated with increased levels of potato leaf-roll virus.
- the fungicide supressed the blight fungus, but also killed a fungus that was pathogenic to aphids, meaning that the aphid population increased, and they acted as vectors for the potato leaf-roll virus.
- It could’ve also resulted in the aphids themselves causing enough physical damage to be a problem, requiring another control.
- for example, fungicide sprays for late blight fungus were associated with increased levels of potato leaf-roll virus.
- We never really know what the full consequences of control strategies are going to be, and sometimes, especially with chemical controls, they can be problematic.
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Integration provides better control
- Can control multiple pests with the same strategy
- = ↑ profitability
- Back-ups in case certain control strategies fail or aren’t sufficiently effective.
- Basically, increasing the number of practices decreases the number of pests that can withstand any one, or combination of, strategies
- = ↑ reliability
- = ↑ robustness
- = ↑ effectiveness
- Basically, increasing the number of practices decreases the number of pests that can withstand any one, or combination of, strategies
- Can control multiple pests with the same strategy
Explain this table, what tolerance ratio refers to, how to calculate it, and why Bt has such a low one.
Something similar was asked as a previous exam question.
The tolerance ratio is calculated as the LC₅₀ of the test strain / the LC₅₀ of the standard strain. (LC₅₀ = lethal concentration for 50% of population).
In other words, it gives a ratio of how much pesticide is required to kill the tolerant strain vs the standard strain.
So a tolerance ratio of 10 would mean that 10x the amount of pesticide (recommended dose) would be needed to kill 50% of the resistant/’test’ strain vs the ‘standard’ strain.
Why Bt has such a low tolerance ratio
Pesticides have particular modes of action; i.e. strategies for defeating the pest’s defences.
Biological controls provide more than one mode of action, which is far more difficult for a pest to build a resistance to.
Are Encarsia formosa (parasitic wasps) a good choice of predator for greenhouse tomato crops?
They can be, depending on the variety of tomato.
They’re predators of whitefly, laying eggs in the nymphs.
However, they don’t like the long hairs found on the leaves and stems of some tomato varieties (which actually act as a defence mechanism for pests), and so aren’t a going to be very successful with these varieties.
What is the EIL?
EIL = Economic Injury Level
EIL = [pest] where crop loss ($) = cost ($) of controlling the pest
i.e. the density of a pest where the loss caused by it is equal in value to the cost of controlling the pest.
Define ET (in terms of IPM) and give another name for it.
ET = Economic Threshold, aka “Action Threshold”
ET = pest population density where management is required to prevent an increasing population from reaching the EIL.
Would you get any benefit by controlling pests once they reach the EIL?
No, because the cost of controlling the pest is the same as the value of damage the pest is causing.
Would you get a benefit from controlling a pest once it reaches the ET?
Yes.
The goal is to control pests once they reach the ET to prevent them from reaching the EIL.
In other words, you want to control them while the cost of control is < the value of the damage they will cause (unchecked).
How are economic thresholds calculated?
Using regression of yield on pest population density or levels of damage.
Most ET are based on empirical observations and trial and error, and are usually good enough.
e.g.
- Choose a range of action thresholds that spans the expected threshold (e.g. pests/leaf, pests/plant)
- Trial each threshold in replicated fields
- Record yields, costs, and financial returns
- yield vs action threshold (# pests/leaf (or plant, whatever))
- # sprays vs action threshold (# pests/leaf)
- gross income and cost of control vs action threshold
- net income vs action threshold
- Determine which action threshold provides the best net returns
- best action threshold = the highest point (net income) on graph.
How does the optimal ET change depending on the value of the crop and cost of spraying?
- As the value of the crop increases (relative to the cost of spraying), the optimal ET threshold (i.e. number of pests you’d tolerate) decreases.
- i.e. as the value of the crop approaches the value of control, it is better to hold off on controls to save money.
- As the cost of spraying increases relative to the value of the crop, the optimal ET increases (i.e. will tolerate more pests
a) Draw a graph of the population density of a hypothetical pest over time with appropriate labels. Show the EIL and ET.
b) List TWO (2) key factors that determine the ET.
a) see attached image
b)
- the value of the crop ($/t)
- the cost of controlling the pest ($)
An action threshold for native budworm attacking chickpea in Northern Australia has been reported as 6 larvae/m². Assuming the price is $500/tonne and the cost of an insecticide spray is $80/ha:
a) How could the accuracy of this threshold be verified? (10 min)
b) What would happen to the threshold if the cost an an insecticide spray dropped to $60/ha? Explain. (5 min)
a)
- Trial various thresholds either side of the reported thresholds on replicated field trial.
- Record yields, costs, and financial returns
- yield vs action thresholds
- # sprays vs action threshold
- gross income and cost of control vs action thresholds
- net income vs action thresholds
- Determine which action threshold provides the highest net income return.
b)
- The optimum action threshold would go down.
- As the cost of control decreases, the amount of pest damage (i.e. the population density) that you’re going to tolerate before taking action is going to decrease.
- This will depend on the crop and the value of damage relative to pest population density.
How would you calculate/summarise the expected losses (in $/ha) from this table?
Sum(losses ($ha)*probability of losses)
In other words, (0*0.66)+(10*0.28)+…
Which is the better option, based on this table?
Option 1: Hard insecticide
Option 2: Soft insecticide
Option 3: Bt spray
Option 4: No action
Option 2 or 3.
Which would be the best is going to depend on:
- The likelihood of the crop value changing over time, in what direction, by how much, and what the goals of the producer is.
- ↑ crop value = ↓ the amount of pest damage you’d be willing to tolerate, meaning the greater the degree of control you might be aiming for (lean towards Option 2) .
- How it fits in with an IPM strategy
- Might not want to use chemical control methods in order to capture the benefits achieved by maintaining predators
- secondary pests
- pest resurgence
- Might not want to use chemical control methods in order to capture the benefits achieved by maintaining predators
What were the results of switching from insecticides to IPM in a study by Hardman et al. (1993) in a citrus orchard in Queensland?
Costs: much lower (about half) after switching
% 1st grade fruit (i.e. fruit quality): comparable or slightly better
Result = increased profit
Why do we use degree days as the most common development rate model for pest forecasting?
Because insect developmental time is directly related to temperature.
↓ T = ↑ developmental time
Why does the developmental rate drop off after ~32 °C?
The high temperature causes damage to certain enzymes, which increases mortality.
What is the arrow pointing to?
(The bottom axis is temperature)
The developmental threshold (the temperature below which the developmental rate effectively = 0)
