ET, EIL, ACTION THRESHOLDS, Grower Thresholds

1. Economic Injury Level
( EIL )
Economic Threshold
( ET )

2. IPM Theory
 IPM is posited on the premise that certain
levels of injury from pests are tolerable
 Why?
 damage curve, economics, environmental degradation,
ecological backlash (replacement, resurgence,
resistance)
 Without that premise, we are reduced to pest
control (identify and control)
 How then do we determine how much injury is
tolerable?

3. IPM -Theory
 The cornerstone of IPM is knowledge of the pests
attacking a crop and an understanding of the
relationship of density of those pests to crop damage.
 Therefore, every IPM program is dependent upon
periodic scouting to ascertain pest density and upon
establishment of densities when treatment is warranted,
i.e. thresholds.

4. Pest – Damage Relationship
Linear damage relationship
1. Disease transmitter pest.
2. Late pest infestation when crop
could not recover or compensate
the damage.
Threshold damage relationship
1. Economic damage occurs only at
certain level of pest population

5.  Economic injury level was developed to provide objective guidelines
for making informed decisions about control measures (pesticide
use).
 The EIL is the pest density or level of crop injury that will result in
yield loss equal to the cost of managing the pest.
 It is necessary to calculate the cost of control & the loss of estimated crop
yield and compare them to know whether the economic injury level
has been reached.
 The EIL is based on the economic loss caused by each pest and also
the fluctuating values of crop market price and control costs. As the
market value of the crop decreases, the EIL increases. Producers will
be less inclined to control a pest as commodity prices drop.
 As the cost of pest control increases, the EIL increases. More
expensive control measures require a higher level of pest infestation
before treatment is justified.

7. Economic Threshold
Level (ETL )
Tolerance
Level
ACTION
THRESHOLDS

8.  The economic threshold ( ET ) or action threshold:
 Pest density or level of crop injury at which controls
should be applied to prevent an increasing pest
population from reaching the economic injury level.
 The ET represents a pest density lower than that of the
EIL so that the producer has time to implement the
control measure before the EIL is reached.
 The ET is often set arbitrarily at 80 % of the EIL to
buffer crop producer from preventable economic yield
loss.

11. The economic injury level is the pest density or level of crop injury that
will result in yield loss equal to the cost of managing the pest

12. EIL Calculation
EIL =
commodity value at harvest ( price/kg) * damage coefficient (kg/ du. / #pest /du. )
cost of control ( price/ du. )

13.  EXAMPLE:
 Cost of control :
= $6/DU. for material + $1.5/DU for application = 7.5 $ /DU.
 Loss of estimated crop yield:
 Crop market value 2.75 $ / BOX
 Estimated yield loss 2.5 BOX/DU.
 Estimated control percentage = 75%
Loss of estimated crop yield
=Crop market value * Estimated yield loss * Estimated control percentage
=($2.75/BOX) * 2.5 BOX/DU) *(0.75) = 5.16 $ /du
 Because the cost of control ($7.5) is greater than the economic
loss of estimated crop yield ($5.16), this field has not reached the
EIL.
Economic injury level (EIL) : is the pest infestation point at which the cost of
control equals the loss of estimated crop yield.

14.  The formula basically says that economic damage (=financial loss) begins at
the point where costs of damage (yield loss due to insect/disease damage)
are equal to the cost of control (costs of pesticides for example).
 However, to actually calculate the threshold level for your own field situation
is very difficult as most of the values that should be included in the equation
are not known today, or can just be roughly estimated. That results in a very
theoretical value!
 The thresholds vary with stage of crop growth, with costs of pesticides or
labor, with environmental conditions, with market prices, etc., etc. and can
therefore be very different for a region, for a season, for a field!
 in practice, most economic threshold levels are based on fixed infestation or
damage levels. They do not consider the ability of the crop to compensate
for (a large part of the) damage from neither insects nor the natural enemy
population that may control the pest insect to an acceptable level. Many
other factors like weather conditions, personal health, etc.

15.  Limitations of the EIL & ET Concepts :
 We should realize that many factors have limited both the
design of new economic thresholds and the development
of existing ones. Some of the major limitations include:
 Lack of a thorough mathematical definition of the ET.
 Lack of valid EILs due to difficulties of making precise
estimates of crop loss and yield functions in response to pest
population.
 Inability to make cost effective and accurate population
estimates.
 Inability to predict critical ET variables such as market values
and population trends.
 Lack of a simple means to incorporate externalities, especially
environmental costs into EILs.
 Subjective nature of EILs. Depending on an individuals
circumstances and viewpoint, the EIL could vary widely even for
the same pest on the same crop.

16. GROWER THRESHOLDS
 Development of thresholds can be accomplished by close
monitoring of pest levels and by keeping accurate records over
many different growing seasons.
 These records need to record pest population and yield.
 A growers thresholds can be based on published thresholds, but
must be evaluated and suited to the growers particular
environment and crop conditions.
 For example, if the published Sweet Potato White Fly threshold
is found to be 20 adults per leaf, a grower can monitor their field
and control white fly if found in numbers of 5, 10, 20, 25 adults
per leaf on different fields or parts of the farm. Then keep track
of the effect of these different populations on yield.

17. MMS TO FARMERS
 Economic Threshold Level may give a very
general indication for the number of insects that
can be tolerated on a crop but they are seldom
specific for the situation in the field today.
 Be very critical to these threshold levels and
monitor your filed regularly to check for yourself
in your own field what decision need to be taken

18. Factors involved in decision making
for ETL and for AESA

19. “To Keep Pests Below the
Economic Injury Level”
 Economic Injury Level:
 Cost of control = $ amount of damage caused by the
pest
 Includes amount of pest damage
 Cost of each control practice
 Are determined through extensive research
 Economic Injury Level is the information that is
necessary to develop an Economic Threshold, which is
used by crop advisors

20. Economic Threshold
 Pest Population at which a grower must take
action to prevent a pest populations from
reaching the economic injury level
 Economic threshold is slightly below the economic
injury level
 Pest populations must be increasing

21. Time
Pest
Density
Economic Injury Level
Economic Threshold
Pest Population

22. Economic Threshold Concept
doesn’t work for all pests and pest
types
Insects
Weeds
Diseases