TDOC

z TA245.7 3'16“ 
B873 February 1990
NO.1644

 

Economic Decision Criteria

for Fleahopper and Bollworm

Management in Cotton:
Texas Coastal Bend

 

3}: , - . % . _ - . . . “a



 

The Texas Agricultural Experiment Station, Charles J. Amtz Director
The Texas A&M University System, College Station, as

CONTENTS

Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 1

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 2

Literature Review . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 2

Study Area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 3

Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 3
Insect Pest Injury - Plant Yield Loss Models. . . . 3
Cotton Fleahopper . . . . . . . . . . . . . . . . . . . . . . . . .. 3

Bollworm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 3

Economic Decision Model . . . . . . . . . . . . . . . . . . . 4

Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 4

Yield Decline: Fleahopper . . . . . . . . . . . . . . . . . . .. 4

Yield Decline: Bollworm . . . . . . . . . . . . . . . . . . . . .. 6

Economic Impact . . . . . . . . . . . . . . . . . . . . . . . . . .. 6

Summary and Conclusions . . . . . . . . . . . . . . . . . . .. 10

Limitations of the Study . . . . . . . . . . . . . . . . . . . . . .. 10

Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . .. 11

Literature Cited . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 11

Appendix1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 13

Appendix 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

K Economic Decision Criteria for Fleahopper and
a Bollworm Management in Cotton:
Texas Coastal Bend

Sharif M. Masud
John H. Benedict
Ronald D. Lacewell‘

Abstract

This study focused on two areas. One was a
method (1) for incorporating economic decision
criteria into models of plant damage from insect pests
and (2) for developing an economic decision model
for cotton pest management in the Texas Coastal
Bend. The second was applying the economic
decision model to alternative levels of fleahopper and
bollworm damage and thereby comparing economic
and yield decline losses for cultivars and growth
stages at infestation.

P Lint yield reductions caused by cotton fleahoppers

i, ere estimated for eight cotton cultivars for the
growth period of the fifth true-leaf through the first
week of bloom. Yield reductions were estimated for
fleahopper infestation at levels of 3%, 10%, 15%, and
30%. The analysis suggests that cotton cultivars are
not equally affected by infestations of fleahoppers.
Although SP-37H incurred no yield reduction at the
30% level of fleahopper infestation, CAB-CS, SP-21,
SP-21S, SP-37, and RDC-102 were highly sensitive
to fleahoppers, and treatment was economical at
levels of infestation as low as 3%.

The model lint yield reductions caused by
bollworms were estimated for four cotton cultivars for
the growth period of the sixth true-leaf through the
first week of bloom at levels of bollworm-damage
squares of 3%, 10%, 15%, 20%, 25%, and 30%. The
four cotton cultivars, CAMD-E, SP-37, STV-213, and
RDC-102, experienced yield reductions from bollworm
injury as low as 3% damaged squares; treatment was
economical at levels of damaged squares as low as
4%.

At lint prices of 50¢, 65¢, and 80¢ per pound,
economic losses per acre were estimated for cotton

fleahopper infestations, assuming no insecticide
treatment. Economic losses per acre varied con-
siderably between cultivars and levels of infestation
as the fleahopper infestations were varied from 3% to
30%. At the same alternative lint prices, however,
economic losses per acre for bollworm infestations
were only moderately different between culitvars and
levels of infestation. This analysis indicates that for
CAMD-E cultiver, the breakeven treatment point is at
the level of 23% fleahopper infestations and at 4%
bollworm-damaged squares.

This modeling of various scenarios provides a
general guide for producers in the region relative to
the potential economic injury of cotton fleahopper
and bollworm. In particular, results indicate a strong
economic incentive for chemical control at very low
infestation levels when numbers of insects and injury
are increasing. The information emphasizes the need
to continue development of integrated pest
management technology. Further, these results in-
dicate that the economic incentive differed among
cultivars, the two insect pest species, and the growth
stage of the plant when attacked.

Estimates of yield decline and economic impact
presented herein were not considered for all the
dynamics of crop production, such as weather,
continuous insect infestation, and simultaneous
infestations of fleahopper, bollworm, etc. A second,
future infestation of an insect pest was not included in
the projections. In addition, the study did not consider
the potential infestation of other species of late-
season insect pests, the effect of control decisions on
beneficial insects, or the potential costs involved if
insect pests develop resistance to insecticide.

Key words: Economic decision model, fleahopper, bollworm, yield decline, economic loss, breakeven

treatment

in

‘Respectively, visiting assistant professor, Agricultural Economics Department; professor, Texas Agricultural Experiment
Station, Entomology Department, Corpus Christi, Texas; and professor, Agricultural Economics Department, Texas

A&M University.

Introduction

The cotton fleahopper Pseudatomoscelis seriatus
(Reuter) and the bollworm Heliothis zea (Boddie) are
distributed throughout the Coastal Bend region of
Texas. These pests appear to have become in-
creasingly important economically because of the
widespread adoption of short-season cotton varieties
and accompanying changes in cultural practices.
Intensive insecticide application for the cotton flea-
hopper and bollworm reduces population densities of
the beneficial insects and spiders. For control of the
cotton fleahopper and bollworm on short-season
cotton, insecticides are either applied as a scheduled
preventive treatment or, more commonly, when
damage becomes visible and reaches or exceeds a
fixed arbitrary treatment threshold.

Neither of these approaches is entirely satis-
factory as a pest management practice or from an
economic viewpoint because the possible outcomes
for treatment of a particular insect infestation cannot
be predicted economically or biologically. The pest
manager cannot optimize his/ her investment in pest
management or reduce risk of economic losses.
Insecticides applied for the cotton fleahopper, boll-
worm, or boll weevil can also induce the occurrence
of late-season tobacco budworm, especially if harvest
season is prolonged (Rummel et al. 1986). Efficient
management practices for these pests, therefore,
depend greatly on making biologically, ecologically,
and economically correct integrated pest management
(lPM) control decisions.

Short-season cotton production techniques are
an integral part of the lPM program in the Texas
Coastal Bend, and determinations of the economic
injury level (EIL) (Benedict et al. 1989) are basic to
lPM. The primary goal of lPM is the maintenance of
pest damage and subsequent yield loss below a pre-
established and economically defined ElL (Schneider
et al. 1986). The ElL has been defined as that pest
density at which economic damage results in an
economic yield loss (loss of returns) equal to the cost
of controlling the damage. Traditionally in the ento-
mological literature, economic threshold level (ETL)
has been defined as that pest density at which control
measures are imposed to prevent an increasing pest
density from reaching the ElL (Rabb et al. 1974, Smith
1971, Stern 1973, Stern et al. 1959). The general
absence of accurate and statistically justifiable ElL's
that clearly predict the economic need for artificial
control measures, however, has been considered a
major reason for the confusion over “when to treat" in
lPM today (Van den Bosch et al. 1971).

As crop profit margins narrow for farmers, pro-
duction systems must be fine-tuned to reduce the risk
of economic loss. Thus, if scientists would integrate
fundamental insect injury/ plant response studies of
cotton fleahopper and bollworm with economic
models, farmers would have a more accurate and
rational basis for decisions about cotton production.

Recently, Zummo (1984) developed bollworm
ElL's for a range of control costs, three crop ages,
and four cotton cultivars in South Texas. His ElL
calculations were based on the regression slope of
the percentage of damaged squares to the percentage
of lint yield loss. In addition, Benedict and co-workers
(unpublished data, 1983-86) developed fleahopper
injury-yield response regression equations for four
short-season dryland cultivars using the number of
fleahoppers present rather than the square damage.
We used these pest damage regression relationships
as the foundation to develop an economic decision
model for insect pest management in cotton.

The incorporation of economic decision criteria
with selected regression models was designed to
provide an integrated decision model that would
indicate when the cost from damage of insect pests
was equal to or greater than the control costs. The
cost-benefit analysis was a marginal analysis that
indicated expected value of the lint loss compared
with change in costs of insecticide applications,
harvesting, ginning, and other yield-related costs. By
incorporating economic decision criteria into pest
models, a more precise timing of needed insecticide
applications can be established according to the
dynamics of a given production region or year. The
integrated decision model was programmed for a
microcomputer and is being field-tested at selected
farms.

The purposes of this report are, first, to present
the method used to develop the decision model and,
second, to demonstrate use of the model in evaluating
insect management decisions considering alternative
lint, pest control, and other input prices. This second
purpose is the major focus of this report. Results of
these analyses provide a basis for developing general
recommendations of insect pest control on cotton in
the Texas Coastal Bend. The model is applicable to
other cotton-producing regions across the U.S.

Literature Review

McCarl (1981) developed a detailed literature
review concentrating on economic aspects of insect
pest management. The concept of the static economic
threshold of insect pests triggering a need for
insecticide spray (Stern et al. 1959) provided the
stimulus to work on the cost/ benefit of pest control,
especially insecticides (Headley 1972). Shoemaker
(1973a, b) laid the theoretical groundwork for estab-
lishing optimal insecticide use according to a
dynamic-programming approach. Hall and Norgaard
(1973), meanwhile, expanded on Headley's work by
considering the optimal use of pesticides when both
timing and dose were treated as a variable.

According to simulations, the intrinsic growth
rates of pest populations in cotton have a surprising
influence on the economics pest control (T alpaz and
Borash 1974). At higher insect growth rates, for
example, the optimal application policy was estimated
to be fewer treatments but at higher pesticide doses.

Interestingly, this also resulted in higher profits than

K in lower insect growth rates. Regev et al. (1976) used

a simplified version of the Gutierrez et al. (1976)

alfalfa - Egyptian alfalfa weevil model to optimize a‘

profit function for the alfalfa weevil and alfalfa crop.
Talpaz et al. (1978) used the Curry et al. (1980) cotton
and boll weevil model to maximize net revenue and
employed a numerical algorithm when insecticides
were applied to control the weevil. Other such
simulation studies included the analysis of pesticide
use and timing for Lygus spp. control (Gutierrez et al.
1977) and biological control of boll weevil (Murty et al.
1980 and Curry and Cate 1984).

Economic evaluations indicate considerable
success owing to the implementation of pest manage-
ment science. Several studies (Lacewell and Taylor
1980, Masud et al. 1981, and Shaunak et al. 1982)
.indicate that short-season cotton production systems
generally increased yields at less cost and also
decrease pesticide use and farmer risk. Masud et al.
(1985) analyzed the economic value of the uniform
planting date and showed great economic returns
from relatively simple cultural control practices.

Study Area

The study area was near Corpus Christi in the

Coastal Bend region. The climate is intermediate

between that of humid, subtropical coastal area to the
northeast and that of the semi-arid area to the west
and southwest. Average rainfall is 28.5 inches, and
average length of the growing season ranges from
335 days near the coast to 288 days in the western
part of Nueces County. Soil types are mostly dark

loamy and clayey Orelia and Victoria (U. S. Department -

of Agriculture 1965). The main agricultural products
in the region are cotton, grain sorghum, and corn. In
addition, pastureland for grazing cattle is also
maintained.

Methods

The study to incorporate economic decision
criteria into selected entomological models was
designed to assess the economic impact of alternative
pest levels. The economic analysis was a comparison
of expected value of yield loss (less yield-related
costs) to costs of treatment for a selected pest
infestation level.

Insect Pest Injury - Plant Yield Loss Models

Data collected by Benedict et al. (1989) on the
cotton fleahopper and bollworm at Corpus Christi
were converted to a percentage of fleahopper infes-
tations, a percentage of bollworm-damaged squares,
and a percentage of yield losses. The percentages
were transformed to arcsin (in radians) because of
the wide range (0 to 40). This transformation helped in

pstabilizing the error variance and made treatments

and replication effects additive. For both the cotton
fleahopper and bollworm, the insect injury and plant
yield response regression relationships were devel-

oped on four cotton cultivars and three stages of
growth. Results of the estimates along with statistical
interpretations are presented in Ring et al. (1989).
These regression relationships have been developed
into yield reduction equations and were used for the
economic decision model for the two insect pests.

Cotton Fleahopper

Equations of insect injury/plant yield loss for the
cotton fleahopper are as follows, where Y equals a
percentage of yield reduction in pounds of lint per
acre caused by fleahopper damage, and X equals a
percentage of cotton fleahoppers calculated from
numbers per 100 plants:

Growth period ll, i.e., fifth true-leaf through the
first week of bloom:
Cultivars
1. CAMD-E: arcsin \/\7= +1.24 (arcsin w)
- 0.05 (arcsin J7)?
2. SP-37H: No yield loss found.
3. CAB-CS: arcsin Y = -1.89 (arcsin \/)T)
+ 0.03 (arcsin {K2
4. STV-213: arcsin \/\7= +1.60 (arcsin J?)
'- 0.05 (arcsin JY)?
The following relationships for the cotton flea-
hopper were also calculated from published
field studies or from estimates from cultivar field
test comparisons:

5. SP-21: arcsin W= -1.46 (arcsin 
6. SP-21S: arcsin \./\7= -1.64(arcsin  -
7. RDC-102: arcsin \/.\7= -2.15(arcsin 
8. SP-37: arcsin \/\7= -1.60 (arcsin 

There were no models for growth period l, i.e.,
seedling through the fourth true-leaf, and growth
period lll, i.e., second week of bloom through the boll
maturity stage in this study. This was based on the
assumption that cotton fleahoppers do not damage
cotton during these growth periods; thus, insect treat-
ment was not recommended for these two growth
penods. G

Bollworm

The equations for the bollworm were as follows,
where Y equals a percentage of yield reduction in
pounds of lint per acre owing to bollworm damage.

Growth period ll, i.e., sixth true leaf through
the first week of bloom where T equals a
percentage of bollworm-damaged squares:
Cultivars
1. CAMD-E and SP-37: arcsin JV = -0.a3
(arcsin 
2. STV-213: arcsin \/-Y_= -0.68(arcsin \/'IT).
.3. RDC-201: arcsin \/Y= -0.95(arcsin \/T_).

Growth period lll, i.e., second week of bloom
through boll maturity where S equals a per-
centage of bollworm-damaged squares:

Cu/tivars

1. CAMD-E: arcsin \/\7= -0.72 (arcsin/A/S).

2. SP-37: arcsin \/\7= -O.92(arcsin S)

3. STV-213: arcsin _ Y=-0.87(arcsin 

4. RDC-102: arcsin \/7= -0.95(arcsin 
ln addition, published data from other

scientists (Heilman et al. 1981) were used to
determine the following relationships:

Growth period I, i.e., seedling through the
fifth true-leaf where R equals a percentage of
bollworm-damaged terminals.

Cult/vars
1. CAMD-E and SP-37: arcsin \/\7= -0.65
(arcsin R).

2. STV-213: arcsin \/)7=-0.43(arcsin J5).
3. RDC-102: arcsin \/)7= -0.75(arcsin 

The bollworm equations represent a single
infestation of bollworm lasting approximately 15 days.

Economic Decision Model

The economic decision model is composed of
the aforementioned insect injury models and budget-
ing procedures combined with breakeven analysis.
As in the previously discussed pest model, the
economic model for both the cotton fleahopper and
bollworm were built for four cotton cultivars and three
stages of growth. The model is user friendly and
menu-driven. lt was developed to evaluate changes
in yield of lint and seed caused by the level of pest
infestation of fleahopper (as a percentage of infested
plants) and bollworm (as a percentage of damaged
squares). This was accomplished through a subroutine
developed from the insect pest injury models that
estimates percentage of yield decline from the re-
gression slope of percentage of fleahopper numbers
to percentage of yield loss for the fleahopper equation
and the percentage of damaged squares to percentage

of yield loss for the bollworm equation, by cultivar and
growth period. In addition, six equations were included
in the model to calculate (1) yield with bollworm or
fleahopper infestation, (2) lint yield decline and
associated seed yield decline, (3) value of lint and
seed yield decline, (4) reduction in harvest cost
because of less yield, (5) net economic loss, and (6)
insect treatment benefit. A schematic diagram of the
economic decision model is presented in Figure 1.
Data necessary for the economic calculations
include a base lint yield (yield expected without these
insect pests), prices of lint and seed as well as
insecticide treatment costs, total variable production
costs and those per unit costs, total variable pro-
duction and those per unit costs related to yield, such
as harvesting, moduling, hauling, ginning, and bags
and ties. Lastly, the cost per acre for an insecticide
application must be included. These estimated prices
and costs used in the illustration are shown in Table
1. They represent dryland cotton production in the
Coastal Bend (Texas Agricultural Extension Service
1987). These values were used to estimate the lint

yield decline and the economic outcomes for various
cotton production scenarios under alternative levels

of percentage of fleahopper-infested cotton terminals \-

or percentage of bollworm-damaged squares.

Table 1. Assumed yield, price, and production costs
of cotton, Texas Coastal Bend region,

1987.
Fleahopper Bollworm
model model

Lint yield without insect (lb/ ac) 750 750
Lint price (cent/ lb) 658 65a
Seed price ($/ton) 110 110
Total variable costs ($/ ac) 30 30
Cost per treatment for insect

control, including cost of

insecticide and applications

($/ac) 2 7
Stripper harvest cost ($/ cwt) 15 15
Module and hauling cost
($/cwt)
Transportation cost ($/ bale) 5
Ginning, bags, and ties cost
($/ bale) 77 77

aA/ternate/y assumed 50¢//b and 80¢//b.

Results

To estimate lint yield decline caused by the
cotton fleahopper and bollworm infestations in the
Texas Coastal Bend, we set a base yield without
pests at 750 lbs of lint per acre for illustrative purposes.
The base yield may differ by variety and by farm
operator. Regression equations representing the
insect injury/yield loss relationships were used to
estimate the percentage of yield decline for given
pest infestation levels. The estimated yield decline
value was then used to estimate net loss per acre for
alternative scenarios. Scenarios included alternative
levels of percentage of fleahopper infestation and
percentage of bollworm-damaged squares, prices of
cotton lint, different plant growth stages, and different
cultivars.

Yield Decline: Fleahopper

Lint yield reductions owing to cotton fleahopper
infestations were estimated for eight cotton cultivars
for the growth period of the fifth true-leaf through the
first week of bloom (growth period ll) and for six
alternative levels of fleahopper infestation: 3%, 10%,
15%, 20%, 25%, and 30% (Table 2). There were no
yield reductions for SP-37H. CAMD-E and STV-213
cultivers incurred the least amount of yield decline.
For CAMD-E, yield reduction did not occur until
fleahopper density increased to 20%. Of all the
cultivars damaged by fleahoppers, STV-213 incurred
the lowest level of yield decline (1 lb/ac) at the 30%

Pest model:
insect pests
damage function

Insect pests

A . infestation

level

Percentage of
lint and seed
yield decline

Reduction in
lint and seed

l

Value of
production
loss

Net economic loss

Expected yield
with no insect
pests

V

Insect pests
treatment cost

1%

Figure 1.

Reduction
in harvest
cost

Treatment

benefit

>0, treat
<0, do not
treat

Schematic diagram of the economic decision

model for the cotton fleahopper and bollworm.

Table 2. Estimated lint yield reduction by percent-
age of fleahopper infestation and cultivar,
Texas Coastal Bend regionfi

Table 3. Estimated lint yield reduction by percent-
age of bollworm-damaged squares and
cultlvar, Texas Coastal Bend region!

Cultivar Percentage of plants with fleahoppers Cultivar Percentage of bollworm-damaged squares
3 10 15 20 25 30 3 10 15 20 25 3O
-------------- -- (lbs/awe) -------------- ---—-----Yield reductions (lbs/acre)---------
1) CAMD-E 0 0 0 1 14 44 CAMD-E 16 52 79 106 133 161
2) SP-37H 0 0 0 0 0 0 SP-37 16 52 79 106 133 161
3) CAB-CS 56 130 160 177 184 184 STV-213 10 35 54 72 91 111
4) STV-213 O 0 0 0 0 1 RDC-102 20 68 102 136 171 205
5) SP-21 47 154 226 294 359 421
6) SP-21S 60 190 276 356 430 497 aAssumes the cotton plant stage of growth to be the sixth true-
7) M30102 1QQ 395 427 52g 511 674 leaf through the first week of bloom.
8) SP-37 57 182 265 342 414 480

aAssumes the cotton plant stage of growth to be the fifth true-leaf
through the first week of bloom.

fleahopper density level. This cultivar incurred no
yield decline at fleahopper densities of less than 30%.
For the remaining cultivars, yield reductions varied
considerably as the percentage of fleahoppers in-
creased from 3% to 30% For example, CAB-CS yield
reductions ranged from 56 lbs/acre to 160 lbs/acre
as fleahopper densities increased from 3% to 15%.
Yield reductions however became more stable at
fleahopper infestation levels of 20% to 30%.

Lint yield reductions for SP-21 increased steadily
as fleahopper infestations increased from 3% to 30%.
Yield reductions of SP-21S and SP-37 cultivars
followed the same pattern as that of SP-21. However,
SP-21S sustained higher yield decline than did SP-
21, and SP-37 sustained a slightly lower yield decline
than did SP-21S as the percentage of fleahopper
densities increased from 3% to 30%. The highest yield
reductions were incurred by ROG-102. Yield was
reduced about 100 lbs/acre of lint at a fleahopper
infestation level of 3% and increased to a yield loss of
about 674 lbs/acre at a fleahopper infestation level of
30%. RDC-102 is more sensitive to fleahopper infesta-
tions because it is smooth and glandless. From
variety testing, entomologists know that ROG-102
sustains more damage and yield loss from fleahoppers
than do CAB-CS or SP-21S.

Yield Decline: Bollworm

Lint yield reductions caused by a single bollworm
infestation were estimated for four cotton cultivars for
the growth period of the sixth true-leaf through the
first week of bloom (growth period ll) and for six
alternative levels of bollworm-damaged squares, 3%,
10%, 15%, 20%, 25%, and 30% (Table 3). Similar
analyses could be done to estimate lint yield reduc-
tions from bollworm infestations for growth period l,
seedling through the fifth true-leaf, and for growth
period lll, second week of bloom through the boll
maturity. In this example, however, yield reductions

from bollworm were not estimated for growth period I
and growth period lll.

Lint yield reductions for the four cotton cultivars
started at 3% bollworm-damaged squares and in-
creased linearly as the percentage of bollworm-
damaged squares progressed to 30%. For CAMD-E
and SP-37 cultivars, yield reductions were found to
be identical at each of the selected levels of per-
centage of bollworm-damaged squares. Yield reduc-
tions ranged from 16 lbs/acre at 3% bollworm-
damaged squares to 161 lbs/acre at 30% bollworm-
damaged squares for these cultivars. STV-213 cultivar
experienced the lowest yield reduction among the
four cultivars as a result of bollworm infestations.
Yield reductions for this cultivar was 10 lbs/acre at
3% bollworm-damaged squares and 111 lbs/acre at
30% bollworm-damaged squares. Finally, of the four
cotton cultivars affected by bollworm, RDC-102 ex-
perienced the highest lint yield reduction at each of
the six levels of bollworm-damaged squares. For this
cultivar, yield reduction ranged from 20 lbs/acre at
3% bollworm-damaged squares to 205 lbs/acre at
30% damaged squares (Table 3).

Economic Impact

Cotton yield loss by cultivar demonstrates the
estimated effect of insect pest infestations on dryland
cotton yields in the Texas Coastal Bend. A critical
issue, however, is the effect on costs and returns to
cotton producers. By applying the values in Tables 1,
2, and 3, net economic losses (lint and seed) per acre
were estimated under alternative levels of percentage
of fleahopper infestation and percentage of bollworm-
damaged squares by price of cotton for each cotton
cultivar and each insect treatment cost. In general,
the net economic effect with no insecticide treatment
for each cotton cultivar was estimated by subtracting
the reduced harvest and processing costs caused by
a yield decline from the value of yield decline. To
calculate the value of a per acre yield decline,
assumed lint prices were alternately placed at $0.50,
$0.65, and $0.80 per pound. An estimate of the
potential economic benefit to the farmer from insect
treatment was obtained by subtracting the treatment

cost (material and application) from the net economic
loss expected with no treatment.

F/eahopper. Net economic losses per acre
caused by fleahopper infestation, assuming no in-
secticide treatments, were estimated for seven cotton
cultivars for the growth period of the fifth true-leaf
through the first week of bloom and at fleahopper
infestation levels of 3%, 10%, 15%, 20%, 25%, and
30%. Net losses were not estimated for SP-37H
because no yield losses were estimated for this
cultivar.

An example of output from the economic decision
model is presented in Appendix 1 and summarized in
Table 4. ln the example, we compared per acre
economic impact of fleahopper infestations with and
without insect treatment for CAMD-E. Estimates of
economic impact also include a 23% fleahopper
infestation level to illustrate the approximate break-
even point for insect treatment. As indicated earlier,
yield reduction for CAMD-E did not occur until the
percentage of fleahopper infestation increased to
20%. Thereafter, yield decline continued steadily to
about 44 lbs of yield/acre at 30% fleahoppers. The
resulting value of yield decline assuming the lint and
seed price of $0.65/ lb and $110.00'/ton, respectively,
was $0.93/acre at the 20% infestation level and
increased to $32.48/acre at the 30% fleahopper
infestation level. A decline in yield from fleahopper
infestation resulted in less cotton harvested. The
reduction in harvest cost owing to yield decline was
estimated to be $0.42/acre at the 20% fleahopper
infestation level (Table 4). Reduction in harvest costs
from fleahopper infestation levels of 20°/o to 30% were
not enough to compensate for the decline in value of
the yield. in the absence of any insecticide treatment,
CAMD-E cotton initially incurred a small economic
loss of $0.52/"acre at the 20% infestation level, which
then steeply increased with the increase in fleahopper
densities (Table 4 and Figure 2).

Assuming a treatment cost of $2.00/ acre (insecti-
cide and applications), CAMD-E cotton was not recom-
mended for treatment until the fleahopper infestation
level increased to 23%. At this infestation level, a
reduction in farmer economic benefit by not treating

$Iacre
2s v I

Lint Price

4m:
G

0' soc

O- 05c

ungr-
3

I-aoc

5n

°I. I I ‘i! : f
3 t0 i5 20 25 30
FLEAHOPPEI INFESTATDII! (1)

Figure 2. Economic loss per acre caused by
damage from a range_of fleahopper infestation
levels, asaummlng no treatment (CAMD-E Cotton).

Table 4. Estimated economic impact of a range of
fleahopper infestation levels for CAllIiD-E
cuitiver, Texas Coastal Bend region!

Yield
Fleahopper decline, Valueof Reduction Net Potential
infestation lint yield in harvest economic economic
level cotton decline costb Iossc benefitd

(%) (lb/ac) ($/ ac) ($/ac) ($/ac) ($/ac)

3 0 0 0 0 -2.00

10 0 O O 0 -2.00

15 0 0 0 0 -2.00

20 1 .26 0.93 0.42 0.52 -1 .48

23 6.96 5.18 2.31 2.87 0.87

25 13.81 10.27 4.58 5.69 3.69

30 43.69 32.48 14.47 18.01 16.01

aAssumes the cotton plant growth period to be the fifth true-leaf
through the first week of bloom.

bAssumes a price of 65¢llb for lint and $110/ton for associated
seed.
cAssumes no insecticide treatment for fleahoppers.

dAssumes insect treatment costs (insecticide and application) at
$2.00/acre.

CAMD-E was $0.87/acre (Table 4). Examining the
economic loss at 23% fleahopper-infested plants, we
found the breakeven point for treatment of CAMD-E
to be $2.87/acre. This is the point where the cost of
yield losses from insect damage equals the cost of
control, when the price of lint was set at $0.65/lb
(Table 4 and Figure 2). For a lint price of $0.50/lb, this
breakeven point will be at a higher level of fleahopper
infestation (e.g., 24°/0), and conversely, for a lint price
of $0.80/lb, the breakeven point will be at a lower
level of fleahopper infestation (e.g., 22%).

The estimated economic loss for the other
cultivars, assuming no treatment of fleahopper in-
festation, is presented in Figures 3-8. Of these culti-
vars, STV-213 was the least sensitive to damage and
incurred net economic loss per acre only at the 30%
fleahopper infestation level (Figure 3). Economic loss
among the remaining cultivars differed considerably
as the percentage of fleahopper-infested plants varied
from 3% to 30%. The net economic loss per acre for
CAB-CS reached a peak at the 25% infestation level
and actually began to decline at the 30% infestation
level (Figure 4). The net economic loss per acre for
SP-21 increased linearly as the fleahopper infestation
increased (Figure 5). Although the net economic loss
per acre incurred by SP-21S was higher than that for
SP-21, this loss followed a pattern of increased loss
similar to that of SP-21 (Figure 6). Similarly, the net
losses per acre incurred by SP-37 was slightly lower
than that of SP-21S, and it followed a pattern of
increased loss similar to that of SP-21 and SP-37
(Figure 7). Finally, of all the cultivers, RDC-102 in-
curred the highest net economic loss per acre at
each level of fleahopper infestation (Figure 8).

IIQF Illll

UIOF IIIII

$Iacre

ill , ,
OSJ I -
‘i: °“" 0 um Price
t 0J1 I .'5°‘
9 0- 65¢
8
s "24 ' I-BO:
Q.‘ q |
J 10 15 20 2S 30
FLEICIIQ ZEIAIX (i)
Figure 3. Economic loss per acre caused by damage
from a range of fleahopper infestation levels,
assuming no treatment (STV-213 Cotton).
Slacre
12a ,
I00 -
Llnt Price
Ill Q
' O-soc
.. r 015C
4 2 2 "30;
40 i
2O
' _ L
3 Ill I5 20 25 30
_ 518i $31111 ti)
Figural. Econoniclossperacrecausedbydamage
from a range of fleahopper infestation levels,
assuming no treatment (CAB-CS Cotton).
Slacra
l!‘ I p
Llnt Price
O-soc
O-ssc
I-aoc

 

° l p n Q l
U I j i I I

I IO l5 2O 25 3O
Rim IQTIIi (i)

Figure 5. Economic loss per acre caused by damage
from a range of fleahopper infestation levels, assuming
no treatment (SP-Zt Cotton).

QIQF‘ 4M2

S/acre
ZEU I
F n
20° i I .’ ,\J
180 . ,  I  Lin: Price
‘$00
. v i. O45‘
100 1 r /. .,.°‘

 

3 l 0 l 5 2 0 2 5 30
FLEAHOPPER INFESTATIONS (H

Flgure 6. Economic loss per acre caused by damage from

a range of fleahopper lnfestatlon levels, assuming no
treatment (SP-21S Cotton).

 

$/acre
30° 1
F
a
zso /
a
20o ‘l /Q um m“
150 I/ /° ‘ism
/ /o  0'85‘
10° 1r ‘  ‘ ivfl‘
x4’
5d 
g/
° .% : . . . y:
3 10 l5 2O 25 30
FLEAHOPPER INFEBTATIONS (18)
Figure 7. Economic loss per acre caused by
damage from a range of fleahopper infestation
levels, assuming no treatment (SP-37 Cotton).
S/acre
4001f
I
I/
soc.) I/
I} /0 Um m“
m.- / /O
. 9-90:
0'0!»
I10;
§ 1-0 1-6 2-0 2-5 :0
FLEAIIOPPEI llFEITAflOlll (i)
Flguie 8. Economic loss per acre caused by
damage from a range of fleahopper Infestation
levels, assuming no treatment (RDC-102 ._

Cotton).

4f'\

Bo//worm. Net economic losses per acre from
alternative bollworm infestations, assuming no insect-
icide treatment, were estimated for four cotton cultivars
and for the growth period of the sixth true-leaf
through the first week of bloom (growth period ll). An
example of output from the economic decision model
is presented in Appendix 2 and summarized in Table
5. ln the example, we compared the per acre eco-
nomic impact of bollworm infestations without
insecticide treatment and with insecticide treatment
on CAMD-E and SP-37 cultivars. The economic
impact was also estimated assuming 84% bollworm-
damaged squares by estimating the breakeven point
for treatment. Unlike the fleahopper example, yield
decline for CAMD-E and SP-37 from bollworm infest-
ations started immediately and was foundto be highly
sensitive to bollworms at all levels of damaged squares
(Table 5). The value of yield decline, assuming lint
and seed price of $O.65/lb and $110.00/ton, respec-
tively, was $15.43/acre at 4% bollworm-damaged
squares and increased to about $1 19.00/acre at 30%
bollworm-damaged squares. The corresponding re-
duction in harvest cost ranged from $6.87/acre at 4%
bollworm-damaged squares to $53.20/acre at 30%
damaged squares.

Net loss per acre, assuming no insecticide
treatment on CAMD-E and SP-37 cultivars, was
estimated to be $8.56/acre at the level of 4%
bollworm-damaged squares. This net loss increased
linearly to $66.21/acre at 30% bollworm-damaged
squares (Table 5 and Figure 9). Assuming a treatment
cost of $7.00/acre (insecticide and application),
CAMD-E and SP-37 cultivars were recommended for
treatment at 4% bollworm-damaged squares. This is
because at the level of 4% bollworm-damaged

Table 5. Estimated economic impact by percentage
of bollworm-damaged squares tor CAMD-E
and SP-37 cultivars, Texas Coastal Bend

regionfi
Yield
Bollworm- decline, Value of Reduction Net Potential
damaged lint yield in harvest economic economic
squares cotton decline costb lossc benefitd

(%) (lb/ ac) ($/ac) ($/ac) ($/ac) ($/ ac)

3 16 11.56 5.15 6.41 -0.59

4 21 15.43 6.87 8.56 1.56
10 52 38.83 17.30 21 .53 14.53
15 79 58.58 26.10 32.48 25.48
20 106 78.58 35.01 43.57 36.57
25 1 33 98.85 44.04 54.81 47.81
30 161 119.41 53.20 66.21 59.21

aAssumes the cotton plant growth period to be the fifth
true-leaf through the first week of bloom

bAssumes a price of 65¢/ lb for lint as well as $110/ton for
associated seed.

¢Assumes no insecticide treatment for bollworms.

dAssumes insect treatment costs (insecticide and applica-
tion) at $7.00/ acre.

squares, the value of the expected yield reduction
exceeded the cost of treatment. At this level of boll-
worm infestation, a reduction in farmer economic
benefit by not treating CAMD-E or SP-37 cotton was
$1 .56/ acre (Table 5).

On examining the economic loss at the level of
4% bollworm-damaged squares, we found the break-
even point for the treatment to be $8.56/ acre. This is
the point where economic losses from insect damage
were equal to the cost of treatment, when the price of
lint was set at $0.65/lb (Table 5 and Figure 9). The
price of $0.80/lb of lint increased the yield loss value
ateach infestation level (e.g., 3%); thus we recommend
treatment at a lower infestation level than that were
the price at $0.50/ lb of lint (e.g., 6°/o).

The estimated economic losses from bollworm
infestations assuming no treatment for the remaining
two cotton cultivars are presented in Figures 10 and
11£Net loss per acre among the cultivars (including
CAMD-E and SP-37 cultivars) from bollworm infest-
ations differed moderately. STV-213 incurred the
least net loss per acre at each level of percentage of
bollworm-damaged squares (Figure 10). Finally,
RDC-102 incurred the greatest net loss per acre at all
levels of bollworm infestation (Figure 11).

S/acre
100 up

LIM Prlee

O~M
O- as:

\
\\

- '\
. \\

lOLLUOII-OAIAGED IGMIEI (i)

Figure 9. Economic loss per acre from bollworm-
damaged squares, assuming no treatment (CAMD-E
and SP-37 Cotton).

S/acre
701p

I". -/'
“ -// 

0' ass

/ I-m

MIDI

4°1-

\
- \\

DOLLIOII-OAIAGED SQUARES (Q

Figure 10. Economic loss per acre from bollworm-
damaged squares, assuming no treatment (STV-
213 Cotton).

COOP 4m:

S/acre
12¢ q p

1004,

l0 1 I Llnl Prlce

O- 50¢
0- use

I 00¢

2 5 3O
IOLLIOII-OAIAGED OOUAIEI M)

Flgure 11. Economic loea per acre from bollworm-
damaged aquarea, aaaumlng no treatment (RDC-102
Cotton).

Summary and Conclusions

This paper is concerned with reports on the
development of an economic decision model and
with comparisons of the economic impact of various
insect management scenarios using the model for
cotton pest management in the Texas Coastal Bend.
The economic decision model was used to assist in
evaluating whether or not to treat simulated fleahopper
or bollworm infestations as indicated by the cost of
control versus the cost of insect-related damage.

The model was applied to alternative levels of
percentage of fleahopper infestation and percentage
of bollworm-damaged squares to determine yield
decline by cultivars and growth stage at infestation
and to determine economic loss assuming no in-
secticide treatment. When the net economic loss from
insect pest injury is approximately the cost of treatment
or greater, there is economic incentive to treat. This
study does not include an analysis of secondary pest
outbreaks or of development of pesticide resistance
by insect pests.

Lint yield reductions caused by cotton fleahopper
were estimated for eight cultivars for the growth
period of the fifth true-leaf through the first week of
bloom and for fleahopper infestation at levels of 3%,
10%, 15%, 20%, 25%, and 30%. The analysis indicates
that the cultivars are not equally affected by flea-
hoppers. The SP-37H cultivar incurred no yield
reduction even at the 30% fleahopper infestation
level. ln addition, STV-213 was not affected by flea-
hoppers until the 30% infestation level was reached,
and CAMD-E experienced no yield reductions until
fleahopper numbers reached 20%. The remaining
cultivars, such as CAB-CS, SP-21, and RDC-102,
were highly sensitive to fleahoppers, and treatment
was economical at levels of infestation as low as 3%.

Lint yield reduction caused by bollworms were
estimated for four cotton cultivars for the growth
period of the sixth true-leaf through the first week of
bloom at bollworm-damaged squares of 3%, 10%,

15%, 20%, 25%, and 30%. The four cotton cultivars

1O

CAMD-E, SP-37, STV-213,yand RDC-102 were highly
sensitive to bollworm infestations; yield reductions
occurred at levels as low as 3% damaged squares,
and treatment was economical at levels of infestations
as low as 4%.

At lint prices of 50¢, 65¢, and 80¢ per pound,
economic loss per acre from cotton fleahopper
infestations among the eight cultivars varied consider-
ably as the fleahopper infestations were varied from
3% to 30%. Economic loss per acre was estimated for
no insecticide treatment. At the same alternative lint
prices, the economic loss per acre from bollworm
infestations among the four cultivars were moderately
different. This analysis indicates that for CAMD-E
cotton, the breakeven treatment point is at the level of
23% fleahopper numbers and 4% bollworm-damaged
squares.

These various scenarios provide a general guide
for producers in the Coastal Bend region relative to
economic implications of alternative levels of cotton
fleahopper and bollworm. In particular, this study
indicates economic incentive for chemical control at
a very low level of infestation for some cultivars but
not for others. Economic incentive for chemical control
also depended upon insect pest species and growth
stage of the cotton plant when attacked with both
fleahopper and bollworm. We observed changes in
the average number of days to crop harvest (mean
maturity date) depending upon level of insect infest-
ation, cultivar, and plant growth stage at infestation.
Our data, however, are not complete for all cultivars
and insects and, thus, could not be presented here.

Limitations of the Study

All the dynamics of crop production, such as
weather, continuous insect infestation, simultaneous
infestations of bollworm and fleahopper, or multiple
infestations of insect pests, were not considered in
the estimates of yield decline and economic impact
presented herein. ln addition, we did not consider
potential infestations of other late-season insect pest
species, the effect on beneficial insects, the potential
costs involved if these insects develop resistance to
insecticides, or the economic costs associated with
changes in mean crop maturity dates following insect
damage. Another limitation of this analysis is that
future insect population size with or without control is
not projected. Treatment of these pests at or below
the breakeven infestation level is justified only when
infestations are predicted to be increasing in damage
potential.

A further limitation of this analysis is the thorough-
ness of the insect injury/crop damage equations.
Most of these regression equations were developed
from sound replicated experiments; however, some
were from data taken in only one study in one year
rather than averaged from data collected over several
years and from several studies. One was also esti-
mated from variety test results.

Acknowledgments

Sincere appreciation is extended to Jim Mjelde and
Torn Knight, Department of Agricultural Economics, and
Ray Frisbie, Department of Entomology, all of Texas A&M
University, for their review and suggestions related to this
bulletin. Our appreciation is also extended to Marian
Schneider, Rachel Carrier, and Adrienne Morgan for their
patience and competent work in typing several drafts of this
manuscript.

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12

Appendix 1
Economic Implications of Fleahoppers on CAMD-E Cotton

FLEAHDPPER DEDIEIDN MODEL BY E. MAEJD, R. LACENELL, AND J. BENEDICT
EXPECTED CDTTDN YIELD WITHOUT FLEAHDPPERS PRESENT (LBS/AERE)= 750
EXPECTED PRICE FDR LINT (CENTS/LD)= E5
EXPECTED PRICE FDR EEED <$/TON)= 110

EXPECTED TOTQL VARIABLE COST, EXCLUDING FLEAHOPPER CONTROL AND HARVESTINO CO3?
($/ACRE)= SO

COST PER TREQTMENT FOR FLEAHOFPER CONTROL INCLUDING COST OF INSECTICIDE AND
QPPLICATION ($/QCRE)= 2

COTTON VARIETY =CAMD—E

COTTON PLANT ORONTH PERIOD =5th TFue—1eaF Through 1st Week 0F Bloom
METHOD OF HARVEST=StrippeP I

COET FOR ETRIPPER HARVEST ($/CWT OF LINT COTTON)= 15

MODULE AND HAULINO COST T$/BfiLE)= 5

TOANSPORTATION COET ($/BALE)= 5

OINNINO, BAG & TIEC COST ($/BALE)= 77

I

_~-_--_-_--_-_--_—-1--_--_-.-__--_-_.._.-1.__-@1111--_-—--_-_.—--_--_--_1-<-~>-__--¢-_-_-11111111111

Pct Eleahonmer Yld H/Fieahopper Yld Decline Yld Decline Va?
X) (lbs/ac) (Tbs/ac) ($/ac)
23.00 743.04 6.96 ;.1O
10,00 750,00 0,00 0,00
j ff _ 00 750 ,, 00 0, 00 0 _ 00
20.00 748.75 1.26 0.93
25.00 736.1? 1E.E1 10.17
30.00 7C:.21 43.é° 32.45

._------._--—--_---_-1-~_.--___-__1_-~_._-_—--_-1---—--_--_---_¢--_-i-11111111111111111

13

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