Fwd: GM Crops Increase Pesticide Use

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Thu, 11 Dec 2003 16:22:58 GMT

GM Crops Increase Pesticide Use

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ISIS Press Release 11/12/03

GM Crops Increase Pesticide Use

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Proponents claim that GM crops substantially reduce pesticide use, but new

evidence shows otherwise. Lim Li Ching reports (ching).

A new report from Dr. Charles Benbrook, director of the Northwest Science and

Environmental Policy Center, Idaho, concludes that the 550 million acres of GM

corn, soybeans and cotton planted in the US since 1996 has increased pesticide

use (herbicides and insecticides) by about 50 million pounds. Benbrook is a

respected agricultural economist and was Executive Director of the US National

Academy of Sciences Board on Agriculture from 1984 to 1990.

The report is the first comprehensive study of the impact of all major

commercial GM crops on pesticide use in the US over the first eight years of

commercial use, 1996-2003. Most studies to date have only focused on the first

three years of GM crop adoption (1996-1998), and no study has estimated impacts

in 2002 and 2003.

Benbrook draws on official US Department of Agriculture (USDA) data on pesticide

use by crop and state to calculate the overall impact of GM crops on the volume

of pesticides applied on corn, soybean and cotton. These three crops account for

nearly all the area planted to GM crops in the US. The analysis focuses on

herbicide tolerant (HT) corn, soybeans and cotton; and corn and cotton

genetically engineered to produce the natural insecticide Bacillus thuringiensis

(Bt).

HT crops allow broad-spectrum herbicides to be sprayed over growing plants,

controlling weeds while leaving crops unharmed, making them popular with

farmers. Despite increased seed prices, HT systems have become less expensive,

largely because the price of herbicides containing glyphosate (Roundup) has

fallen by half since HT crops were first introduced. (Crops tolerant to

glyphosate - known as Roundup Ready varieties - are the largest share of acreage

planted to HT crops).

But the fall in price has meant farmers can spray more herbicides without

feeling the economic pinch. In particular, farmers are spraying substantially

more herbicides on HT soybean. Soybean accounts for about 75% of the 400 million

acres of HT crops and 54% of all GM acres that have been planted since 1996.

While total pounds of pesticides applied to Bt corn and cotton have fallen

modestly (see later), the increase in herbicides applied on HT soybeans has been

far greater. This, combined with the dominance of HT soybean, has led to

dramatic change in overall impact of GM crops on pesticide use.

Benbrook calculates the difference between the average pounds of pesticides

applied on acres planted to GM crops, compared to the pounds applied to

otherwise similar conventional crops. In their first three years of commercial

sale (1996-1998), GM crops reduced pesticide use by about 25.4 million pounds,

but in the last three years (2001-2003), over 73 million more pounds of

pesticides were applied on GM acres.

The increase in overall pounds of pesticides applied across the three crops is

due mainly to the need to apply more herbicides per acre planted to HT soybeans.

USDA data show a marked increase in the per acre rate of glyphosate applied to

HT soybeans between 2001 and 2002 – about a 22% increase, from 0.85 pounds per

acre to 1.04 pounds.

This 22% jump was caused by a major price reduction in glyphosate, the need to

control more difficult weeds, and the emergence of resistance and/or lessened

sensitivity in weed species that were once fully controlled by one glyphosate

application. So for HT soybeans, the difference in average herbicide pounds

applied per acre between GM and conventional crops shifted from a reduction of

0.36 pounds per acre in 1996 to an increase of 0.47 pounds per acre in 2003.

Pesticide use estimates for 2003 in the report are preliminary, since USDA will

not release these data until May 2004. However, estimates for 2003 are based on

2002 levels and trends in recent years. Benbrook is of no doubt that average

glyphosate application rates per acre of HT soybeans continued rising in 2003

due to:

Spread of glyphosate-tolerant marestail (horseweed);

Shifts in composition of weed communities toward species not as sensitive to

glyphosate;

Early-stage resistance in some major weeds; and

Substantial price reductions and volume-based marketing incentives from

competing manufacturers of glyphosate-based herbicides.

HT corn technology reduced herbicide use per acre from 1996 through 2001, but

increased use thereafter. The difference in average herbicide pounds applied per

acre between GM and conventional crops shifted from a reduction of 0.8 pounds

per acre in 1996 to an increase of 0.58 pounds per acre in 2003, due to:

Increases in the rate of glyphosate applied per acre driven largely by shifts in

weed communities, resistance, changes in tillage and planting systems, and

significant reductions in the price of herbicides containing glyphosate;

Incremental increases in reliance of farmers on herbicides other than glyphosate

to assure season-long control of grasses in HT corn; and

Downward trend in average rate of application of herbicides on non-HT acres.

The difference in herbicide application rates on HT and conventional cotton

changed much like that of HT corn and soybeans, shifting from a reduction of

0.64 pounds per acre in 1996 to an increase of 0.17 pounds per acre in 2003.

The report acknowledges that the other major category of GM crops – Bt corn and

cotton – continues to reduce insecticide use by 2 million to 2.5 million pounds

annually. The reduction in insecticide pounds applied per acre planted to Bt

corn and cotton ranges from 0.33 pounds in 1996 to 0.06 pounds in 2003, and from

0.38 pounds in 1996 to 0.2 pounds in 2001-2003, respectively.

However, the increase in herbicide use on HT crops far exceeds the modest

reductions in insecticide use on Bt crops, especially since 2001. The

calculations also don’t take into account the volume of Bt toxin that is

continuously expressed in the Bt crops’ plant cells. This amount is significant

compared to the rates of application in today’s low-dose pesticides.

In short, over the last eight years, HT crops have increased pesticide use an

estimated 70.2 million pounds, while Bt transgenic varieties have reduced

pesticide use an estimated 19.6 million pounds. Thus, total pesticide use has

risen some 50.6 million pounds over the eight-year period.

The increase in pesticide use, largely due to increased use in HT crops,

especially HT soybean, is of no surprise, given that scientists had warned that

heavy reliance on HT crops and a single herbicide (in this case, glyphosate) for

weed management might lead to changes in weed communities and resistance. This

triggers the need to apply additional herbicides and/or increase application

rates to achieve the same level of weed control.

Many farmers have had to spray more herbicides on GM acres in order to keep up

with shifts in weeds toward tougher-to-control species, coupled with the

emergence of genetic resistance in certain weed populations.

" For years weed scientists have warned that heavy reliance on herbicide tolerant

crops would trigger ecological changes in farm fields that would incrementally

erode the technology’s effectiveness. It now appears that this process began in

2001 in the United States in the case of herbicide tolerant crops, " said

Benbrook.

According to Prof. Bob Hartzler, an extension weed management specialist from

Iowa State University, glyphosate-resistant marestail in Roundup Ready soybeans

first appeared in Delaware in 2000, spreading since as far west as Indiana, and

identified in the Southeastern US where Roundup Ready cotton is grown. Other

records of glyphosate- resistant weeds (not necessarily linked to HT crops) are

rigid ryegrass in an orchard in Australia and in wheat production systems in

Australia and California, Italian ryegrass in Chile and goosegrass in Malaysia.

Furthermore, waterhemp populations with individuals capable of surviving

‘normal’ user rates were identified in Iowa and Missouri the first year Roundup

Ready soybeans were marketed. While Hartzler doesn’t think that waterhemp can as

yet be considered glyphosate resistant, the potential exists and should be

closely monitored.

Since the first report of glyphosate resistant rigid ryegrass in 1996, four

additional resistant species with this trait have been identified. According to

Harztler, this rate of development suggests that new resistant biotypes will

continue to arise.

Prospects for GM crops leading to reduced pesticide use in the long-term don’t

bode well either. The pounds of herbicides required to achieve acceptable weed

control is rising on most farms planting HT varieties, compared to the rates of

application common between 1996-1998. In contrast, the amount of herbicides and

insecticides applied per acre on conventional farms continue to trend downward

as a result of incremental shifts toward newer low-dose pesticides and

regulatory restrictions phasing out high-dose herbicides.

As a result, the difference in total pounds of herbicides applied on HT versus

conventional acres has increased steadily since 2000. Given the emergence and

spread of weeds resistant or less sensitive to glyphosate, this difference is

likely to widen further if HT technology continues to be relied on as heavily as

in recent years.

Sources:

*******

Benbrook CM (2003) Impacts of Genetically Engineered Crops on Pesticide Use in

the United States: The First Eight Years, BioTech InfoNet, Technical Paper No 6,

Nov 2003, http://wwww.biotech-info.net/technicalpaper6.html

Hartzler B ‘Are Roundup Ready weeds in your future II’, Submission to UK GM

Science Review, 28 February 2003,

http://www.gmsciencedebate.org.uk/topics/forum/0051.htm

 

 

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