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Maximum Tolerable Levels and Economic Thresholds in Pest Management, Slides of Pest Management

The LNM Institute of Information TechnologyPest Management

The concept of maximum tolerable levels (mtl) and economic thresholds (et) in pest management. The importance of these levels in decision making and provides a detailed explanation of how ets are calculated using the basic eil model. The document also touches upon the advantages of using thresholds in pest management and mentions some examples of their application.

Typology: Slides

2012/2013

Uploaded on 08/31/2013

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Decision Making
• Have discussed the “Maximum Tolerable Level”
but have not defined it.
•Several Points to Make:
– More than 1 “Level” is usually needed.
–There are many kinds of such levels (cf. p. 200 – 201
in text for one list).
– “Action Levels” or “Thresholds” are one general
method of decision making. We will discuss the other
one (Optimization) later.
•The leader in this field has been L. Pedigo. Be
sure & read his article in the “Reading
Assignments”
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Download Maximum Tolerable Levels and Economic Thresholds in Pest Management and more Slides Pest Management in PDF only on Docsity!

Decision Making

  • Have discussed the “Maximum Tolerable Level”

but have not defined it.

  • Several Points to Make:
    • More than 1 “Level” is usually needed.
    • There are many kinds of such levels (cf. p. 200 – 201 in text for one list).
    • “Action Levels” or “Thresholds” are one general method of decision making. We will discuss the other one (Optimization) later.
  • The leader in this field has been L. Pedigo. Be

sure & read his article in the “Reading Assignments”

The General Problem

Maximum Tolerable Level

Time (Weeks)

Pest Population Density

One problem is that we need to allow for management

response time – The time between when a control decision

is made and when it takes effect

Maximum Tolerable Level

Time (Weeks)

Pest Population Density

1 2 3 4 5 6 7 8

Assume it takes 1 week to decide a control is needed, apply it, and for it to work

Decision must be made here

The other problem is uncertainty

Maximum Tolerable Level

Time (Weeks)

Pest Population Density

1 2 3 4 5 6 7 8

Quick Notes on EILs & ETs

  • ET is always < EIL
  • Units of ET & EIL are the same
    • Often pest density (absolute or relative)
    • Can also be injury (e.g. % defoliation)
    • Can also be implicit factors (e.g. leaf wetness)
  • EIL & ET are hard numbers calculated

from equations developed through field

research.

The Basic EIL Model

The basic concept is that the EIL is the point at

which the cost of a control = the value of

damage that will be avoided by the control.

Value of damage avoided is a product of:

Crop market value (V)

Pest population density (P)

Injury caused by each pest individual (I)

Damage resulting from that injury (D)

Proportion of total damage that cannot be avoided by the control (K)

Example

  • Assume:
    • It costs $50/A to apply a given control ( C )
    • A crop is worth $40/bushel ( V )
    • Leaf area equal to two leaves/row foot are

eaten by each pest individual/plant ( I )

  • The loss of two leaves/row foot results in the

loss of one bushel/A ( D )

  • Even if you apply the control, you will still lose

10 % of the crop ( K = 0.1, no units)

Example, Continued

V I D K

C

EIL P

  

 '

  1. 25

40 2 1 0. 10

50 

  

EIL

Here’s how the units balance

lv/row ft

bu/A

pest/plant

lv/row ft

bu

$

$/A

 

EIL

pest/plant

1/1/(pest/plant)

EIL  Result:

EIL = 6.25 pests/plant

One of the principal advantages of EILs

is their objectivity and scientific basis

V I D K

C

EIL P

I, D, and K are determined empirically through field

& laboratory experimentation.

C is, for the most part, easily determined.

For most agricultural crops, V is commonly

available.

Some examples of EILs & their

derivation.

  • EIL for Mexican Bean Beetle in Soybean –

Details the development of an EIL.

  • EILs for sorghum midge on sorghum –

See Table 1 in the middle of the article.

  • Common stalk borer in Nebraska corn
  • Sweet potato whitefly on cantaloupe

How are ETs calculated?

  • Most common method is heuristic. Most

common rule of thumb is 1/3 EIL.

  • Two examples of more formal methods

are:

(1) ET = EIL/ r

(2) ET = EIL/(expected rate of change in

pest population)

Advantages of Thresholds

  • Conceptually easy to understand makes them easy to

implement/adopt. Can also be represented in many formats: single numbers, tables, charts.

  • Scientific basis to threshold criteria
  • Flexibility gives broad applicability
    • Can be applied to a variety of pests in many situations
    • Can utilize many variables as the action variable. Climatic variables often used for pathogens.
    • Have been extended to take into account many other issues. Examples include - Age distribution - Multiple controls (e.g. biocontrol) - Environmental Impacts (i.e. macroeconomic “C” values) - Risk

Closely read the remainder of this

chapter

  • This is the only place where the following

topics are discussed:

  • Use of field history
  • Field location & size
  • Monitoring climate
  • Use of computer/mathematical models
  • Aesthetic effects
  • Risk Assessment
  • Economics