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October 30, 2000


Are Bt Crops Beneficial?: A Critique of Bebrook Report of


A Critique of: An Appraisal of EPA’s Assessment of the Benefits of Bt Crops
by Dr. Charles M. Benbrook, October 17, 2000
Prepared for Union of Concerned Scientists

This Critique of the Benbrook Report is authored by Leonard P. Gianessi

National Center for Food and Agricultural Policy
1616 P Street, NW, Washington, DC 20036
Phone: 202-328-5048 Fax: 202-328-5133 ncfap@ncfap.org

October 31, 2000


On October 20, 2000, the Union of Concerned Scientists submitted to EPA a
report prepared by Dr. Charles Benbrook analyzing EPA’s assessment of the
benefits of Bt crops. Subsequently, the Benbrook report has been posted
on the internet: www.biotech-info.net

The Benbrook report discusses the benefits of Bt field corn, Bt sweet corn
and Bt cotton, with most of the discussion focused on Bt field corn.
Benbrook concludes that although Bt field corn increases yields, these
yield increases are modest and could be achieved easily by alternative
techniques. He presents an analysis that is claimed clearly "to refute"
EPA’s conclusion that Bt corn has reduced insecticide use. His bottom
line is that with relatively modest benefits, the relatively modest risks
of Bt corn should tip the risk/benefit scales against the continued
registration of Bt corn.

Summary of Critique

1. Benbrook concedes that, on average, Bt corn has improved yields and net
returns. He argues that this is modest. 1998-2000 were years of very
light insect pressure and low corn yields, and still, positive benefits
were achieved. Many growers benefited far above the average. In heavy
infestation years the benefits will be much larger. With corn farmers in
economic distress, a technology that improves the bottom line should not
be dismissed.

2. The "alternative methods" that Benbrook touts are not new. They have
been researched for 70 years. Farmers do not use them because they are
extremely complicated, time consuming, would require extensive changes in
farming practices and are not as effective as Bt corn.

3. Benbrook’s manipulation of pesticide use data to show an increase in
insecticide use for the European corn borer is arbitrary and unconvincing.
He leaves out of his analysis the one insecticide that clearly went down
in use because of Bt corn. The insecticides that went up in use are not
used for European corn borer (ECB) control. They are used almost
exclusively for other pests. No entomologist or survey supports his
hypothesis. The available surveys support the EPA conclusion that Bt corn
caused a reduction in insecticide use.

Bt Corn

Benbrook claims that European corn borer management options are available.
He asserts that ECB populations only reach damaging levels a few years out
of every ten. Actually, the opposite is true. ECB populations are at
damaging levels most years out of ten. Benbrook asserts that corn growers
have been managing the ECB adequately most years without Bt corn. This is
not accurate. Survey data from Iowa State University indicate that most
corn growers were not managing the ECB at all. Their strategy was to do
nothing and suffer the yield losses. Some harvested early to minimize
losses to ECB, that can cause plants to "lodge" or fall to the ground and
become unharvestable.

Benbrook asserts that additional ECB control options are available for
corn growers to use. He cites research at Ohio State University where
researchers have studied ECB populations on organic farms in comparison
with neighboring conventional farms. Benbrook reports that the Ohio State
research suggests that differences in nutrient management results in less
damage from ECB on the organic farm. Benbrook incorrectly interprets the
Ohio State research as to the reason for less damage. Benbrook asserts
that conventional farms with standard nutrient applications do not develop
adequate defense mechanisms against the ECB. He suggests that organic
corn develops defense mechanisms through more effective use of
slower-releasing nutrients from manures and other organic types of
nutrients. Actually, the Ohio State research suggests that it is
precisely that conventional corn is so much faster growing, resulting in
more sugars and amino acids in the greener leaves, that attracts more ECB
females that lay their eggs preferentially in the healthier corn. The
organic corn is slower-growing and less attractive. Benbrook’s
misinterpretation results in a convoluted conclusion that organic plants
must be emitting some as-yet-undiscovered chemical signal that repels or
discourages ECB feeding. Is Benbrook suggesting that it is acceptable to
have some undiscovered, unknown, untested chemical repellant in the
organic food supply?

Benbrook incorrectly refers to the Ohio State researcher who conducted
that research, Larry Phelan, as an agronomist. Dr. Phelan is an

Benbrook asserts that there are several known management strategies to
suppress ECB populations, including nutrient management, planting shorter
season corn, chopping up stalks in the winter, planting cover crops, etc.
All of these were available and had been studied long before Bt corn
became available. Benbrook notes that the Ohio organic farm operations
were described over a decade ago in an NAS report. These other systems
have not been adopted widely because they have limited effectiveness and
are much more complicated to implement. Farmers make decisions on types
of tillage practices, nutrient practices and when to plant based on many
factors other than simply insect control. The simplicity and
effectiveness of Bt corn is the reason that growers have adopted this
technology. There has been no shortage of studies regarding alternative
means of controlling the ECB. This pest represents the single largest
effort by the U.S. government to discover or develop biological controls.
All of the biological solutions to this pest problem (researched over the
last 70 years) have had limited or no impact on the ECB.

Finally, Benbrook asserts that crop rotation is a "proven" control
measure. This is totally inaccurate. There are no studies to support
this. The ECB is highly mobile and flies between rotated and non-rotated

Benbrook uses tough language to describe research and technology that
produce only modest improvements in crop yields. He suggests that society
and agriculture might be better served by having the Bt corn researchers
working on other problems. The same line of reasoning might be used to
assess the performance of the considerable research effort regarding
"alternative agriculture" over the past decade. What positive net
benefits have they delivered? Where is the cost-benefit ratio concerning
the Leopold Center, a sustainable agriculture research center in Iowa?

Benbrook claims that insecticide use for the ECB actually increased
following the introduction of Bt corn. He cites no surveys of farmers who
say that they have increased their insecticide use for ECB. He cites no
university entomologists who share his view. The available surveys of
farmers show just the opposite. According to Iowa State University
surveys, insecticide usage among Bt corn farmers is declining. In 1996,
insecticide use declined 13% with Bt corn farmers. In 1997 and 1998, 19%
and 26% of Bt corn farmers stated a reduction in insecticide use from
previous years.

Benbrook's logic in explaining why corn farmers increased spraying for the
ECB is two fold.

(1) Growers have been sensitized to the importance of ECB control because
of all the attention focused on Bt corn. While this is a correct
statement, Benbrook argues that some have decided that rather than
planting Bt corn they would spray an insecticide. This makes no sense.
Benbrook claims that the cost of the Bt seed is an extra $10 an acre; the
cost of a single insecticide spray for ECB control is $14 an acre.
Growers are advised to expect from 67% to 80% control of the ECB by
spraying. Bt corn gives 95% control. Why would a farmer decide to spray
instead of planting Bt corn? Benbrook ignores all of the reasons that
growers traditionally have not sprayed, including the difficulty of
scouting and timing treatments. These problems have not disappeared. The
decision to spray is not as simple as Benbrook implies. However, the
decision to use Bt corn is simple. Given this increased interest in ECB
control and Benbrook’s assertion that alternative non-chemical methods are
cost effective, why have the growers not selected a non-chemical method
instead of spraying?

(2) Benbrook also claims that beneficial insects may have shifted in
importance because of Bt corn. There is no evidence to support this claim
at all.

The data that Benbrook manipulates to support his ideas come from USDA
NASS surveys of corn growers 1995-1999. Since the NASS data do not
identify the target pest in the surveys, Benbrook makes his own
assignments. He misattributes all of the spraying of lambdacyhalothrin,
dimethoate and esfenvalerate to ECB. These pesticides are recommended for
many insect pests in corn, including cutworm, stalk borers, leaf aphids,
adult rootworm beetles, European corn borer, armyworm, grasshoppers and
mites. There is no justification to assign all of their use to ECB. In
fact, it is very likely that the increased use of these compounds is
largely the result of increased in-season sprays for cutworms. Benbrook
assigns 25% of the increase in fipronil and bifenthrin to ECB control,
with the remainder going to rootworm control. Bifenthrin is used
primarily for mite control and not ECB. Fipronil was recommended in 1999
for rootworm and grubs. There is no mention in the University Extension
publications for 1999 of ECB control with fipronil. Benbrook arbitrarily
assigns 25% of its use to ECB control.

Benbrook leaves one key insecticide out of his analysis of trends: foliar
Bt, that was used on 1% of the nation’s corn acreage in 1995 and is no
longer recorded as being used following the introduction of Bt corn. Why
apply Bt foliarly when it is in the plant? Some farmers who report a
decline in use of insecticides following the introduction of Bt corn
undoubtedly were spraying Bt in the early 1990’s.

Benbrook does not consider the likely impact of his recommendation that
EPA cancel the use of Bt corn. He is correct in stating that growers have
become sensitized to the potential damage from the European corn borer.
Many growers have been ignoring the damage from ECB for many years and not
spraying. Now they are planting Bt corn and seeing the positive impact on
yields. What happens if Benbrook’s advice is followed, and Bt corn is
taken away? It is quite likely that insecticide use would increase
dramatically as some growers start spraying.

Benbrook grudgingly concedes that with respect to corn yields that actual
data on the performance of Bt corn lends "partial" support to the
conclusion that planting Bt corn has increased corn yields. However, to
put this yield advantage in perspective, Benbrook cites studies where no
differences in yield were estimated. However, the studies that he cites
were conducted before the widespread introduction of Bt corn and are
merely simulations based on historic ECB populations. Benbrook cites
entomologists who clearly advised growers to think long and hard about the
potential benefits of Bt corn for 2000 based on the light infestations
seen in 1998 and 1999. Their advice was only plant Bt corn if your
experience over time indicates that you are likely to have a damaging
population. This is sound advice. Thus, the real question is who planted
Bt corn and what did they gain by planting it? Averages can be very
misleading. Data from Marlin Rice at Iowa State University indicate that
benefits are not uniform. For example, in 1999, 21% of the side-by-side
comparisons in Iowa indicated a yield advantage for Bt corn of nine
bushels per acre while the remaining 79% indicated no advantage. In 1997,
40% of the comparisons indicated an increased yield advantage of 18
bushels per acre for Bt corn while the remaining 60% produced no
advantage. There are growers who have made significant gains from
planting Bt corn. Three factors must be kept in mind in evaluating Bt
corn’s effectiveness:

(1) It’s early in the adoption cycle. Many growers may try out a
technology to see how it works. They may stop using it if it does not
produce significant benefits.

(2) Many growers may be willing to pay the premium for Bt corn seed simply
for its insurance value. In case it is a bad outbreak year, they are

(3) 1998/1999/2000 were very unusual years in that ECB populations were so
low. A10 or 15 year time horizon may be needed to evaluate the technology

Benbrook states that 1997 was a high infestation year. He is incorrect;
1997 was an average or slightly low infestation year. In a high
infestation year the advantage of Bt corn could be as high as 40 bushels
per acre.

Benbrook suggests that a positive net return of $3.31 per acre from Bt
corn is modest and not important. He needs to be reminded of the
extremely low returns that corn farmers have experienced these past few
years. The $3.31 net return estimate is based on a Bt corn fee of $10 per
acre. In actuality, the Bt corn fee has come down significantly and is
probably closer to $7 per acre on average, that, essentially, would double
the calculation of economic benefit of Bt corn to corn farmers.

Bt Sweet Corn

Benbrook reports that the planting of Bt sweet corn has been limited due
to the unwillingness of shippers to accept the genetically engineered
crop. He suggests that there might not be a huge reduction in insecticide
spraying for sweet corn in Florida because of the emergence of the
silkfly, that he asserts accounts for one-half of the insecticide use in
the crop. This is an unsupported assertion. A University of Florida
researcher presented data to EPA based on experiments in 1998 and 1999,
documenting a reduction from as many as 19 sprays in the conventional
sweet corn to 3 in the Bt sweet corn. Benbrook simply asserts that the
silkfly is the result of intense spraying for other insects. There is no
evidence for this, but if it were the case, would not reduced insecticide
spraying in Bt sweet corn also result in more predators attacking the
silkfly and perhaps further pesticide use reduction? Indeed, the
University of Florida researcher presented data for the EPA Science
Advisory Panel that showed that the numbers of predators and parasitic
insects and spiders were all higher in the Bt sweet corn plots.

Benbrook bemoans the discontinuance of the insect resistance breeding
program for sweet corn in the 1970’s. His implication is that further
work with conventional breeding may have reduced the need for insecticides
or for Bt sweet corn. This is not supportable. Sweet corn breeders have
been focused on flavor and yield, and they have done a great job. What
assurance can Benbrook provide that an insect resistant, conventionally
bred sweet corn cultivar will also taste great? Keep in mind that the Bt
sweet corn is insect resistant, high yielding and tastes great.

Benbrook mistakenly refers to methomyl as an organophosphate; methomyl is
a carbamate.

Bt Cotton

Benbrook reports that EPA estimated a reduction of 7.5 million acre
treatments in cotton as a result of Bt cotton, but he tries to put that
reduction in perspective by suggesting that it may not hold up over time
due to changes in pest populations, resistance, etc.

One value of Bt cotton is that it takes much of the pest resistance
pressure from traditional insecticides for control of the bollworm/budworm
complex (BBW) , consequently prolonging their usefulness for other pests
in cotton fields. Bt cotton is just another control technique for
managing a complex set of pest problems in cotton. One sure way to help
improve resistance management to Bt cotton would be register more
insecticides for cotton and keep currently registered insecticides
available for cotton growers to use. One strong concern that Benbrook did
not mention is that EPA may cancel many of the insecticides that cotton
farmers use and put so much selection pressure on the remaining
insecticides and on Bt cotton that resistance will appear more quickly.

He suggests that much of the reduction may not be due to Bt cotton because
it initially occurred in 1996, following a heavy outbreak year in 1995.
Bt cotton was introduced in 1996 and was planted widely in several states
immediately (77% of Alabama’s cotton acreage). Sprays in Alabama for BBW
went from 6.7 in 1995 to 0.1 in 1996. Bt cotton was responsible for this
reduction. 1995 was a bad outbreak year because the chemicals were not
effective enough.

Benbrook manipulates NASS pesticide use survey data to try and associate
certain chemicals with control of bollworm and budworm. He then asserts
that based on his assignments, insecticide use for BBW actually increased
in certain states (such as Alabama) from 1997 to 1999.

He misattributes insecticides to BBW control. For example, the increase
in Alabama is due to increased applications of aldicarb, a pesticide not
targeted at bollworm/budworm, but one whose increased use in Southeastern
states’ cotton is accounted for largely by nematodes. Benbrook assigns
tebufenozide and carbofuran as BBW insecticides; tebufenozide and
carbofuran received emergency registrations for use against armyworms and
aphids, respectively. There is no need for Benbrook to make the target
pest assignments because cotton entomologists do such assignments every
year, and the results are published in the National Cotton Council’s
Proceedings of the Beltwide Cotton Conferences. According to the Cotton
Council’s reports, in every state, sprays for BBW were reduced following
the introduction of Bt cotton. Sprays for the BBW in Alabama did not
double between 1997 and 1999, as Benbrook’s manipulations suggest.
Rather, the National Cotton Council’s estimates are that between 1997 and
1999, there was a 20% reduction in sprays for the BBW in Alabama.

Benbrook tries to put the reduction of cotton insecticide use in Arizona
in perspective by suggesting that it may be due in large part to the
introduction of new, effective insecticides for control of the sweet
potato whitefly and not Bt cotton. There is no denying the positive
impact of the new insecticides, but to give credit where credit is due, it
is instructive, once again, to examine the National Cotton Council’s
estimates. For Arizona in 1999, conventional cotton growers sprayed once
for bollworm; Bt cotton growers did not spray at all for the pest.