Ten Reasons why farmers should think twice before growing GE crops

E. Ann Clark, Plant Agriculture, University of Guelph (aclark@plant.uoguelph.ca)

The tide appears to be turning against GE crops, but farmers may well be the last ones to know. Many citizen and professional groups are now on record, urging everything from an outright moratorium to a slower, more reasoned approach. For example, on 2 June 99, the National Federation of Women's Institutes voted 7055 in favor vs. 368 against a 5-year ban on the growing of GE crops in the UK.

My goal today is to give you some of the agronomic reasons why farmers should think twice about growing genetically engineered crops.

1. Do you really need what they offer in the first place? For example,

Are European cornborers (Ostrinia nubilalis (Hubner) sufficiently predictable on your farm as to justify the extra expense of growing Bt hybrids as insurance? Sears and Schaafsma (1998) reported that infestations had to be high enough to cut yields by at least 5-8 bu/ac before Bt-corn was economically competitive. They further noted that conventionally-bred cornborer-resistant hybrids performed as well as Bt-hybrids under low-to-moderate cornborer infestations. Thus, unless cornborer infestation is high, you have other, less costly, options besides Bt-corn.

Table 1. When does it pay to grow Bt-corn? (adapted from Sears and Schaafsma, 1998)

Cornborer Infestation Yield Protection by Bt-Corn Bt-Corn Economically Justified? Conventionally-Bred Cornborer Resistance Sufficient?
Low 3-5 bu/ac no yes
Moderate 5-8 bu/ac yes yes
High 10-15 bu/ac yes no

Transgenic solutions come with a price tag that is high, both in terms of dollars and in indirect costs (see below). Whether Bt or herbicide-resistance, be sure you can justify it economically before trying it out.

2. How much of a yield loss can you experience and still make enough money to justify growing GE crops? And keep in mind, that if cornborer risk is high enough to justify using a Bt hybrid, then you'll also need to factor in yield loss on the 20% or more of unsprayed "refugia" set-aside that you are expected to plant to a non-Bt hybrid - without insecticidal protection..

Contrary to what has been promised, GE crops often do not yield more and not infrequently yield less than the best available conventionally bred cultivars and hybrids. Why? Because not all genetic backgrounds within a given crop will tolerate a transgene1, and those that will are not necessarily the highest yielding ones. Further, there is a metabolic cost to expressing herbicide-resistance or the Bt-endotoxin. So, if you were expecting a yield gain - as promised, if we are going to "feed the world" - then you may well have been disappointed. And the fault was not necessarily yours, no matter what they told you.

A recent review of 40 soybean varietal trials in the north central region of the US by Oplinger et al. (1999) found a mean 4% yield drag in RR soybeans. Even comparing the top 5 varieties from each, RR still yielded 5% less than conventional soybeans. In Ontario, most recent data show a 1-3% mean yield drag in RR soybeans (Table 2), and keep in mind that this is relative to the trial mean - not to the highest yielding cultivars. However, the soybean breeder advises that the yield gap is closing. Nonetheless, there is a cost to the crop from expressing the genes for Roundup resistance, and it manifests itself in lower yields.

Table 2. Two-year mean yields of Roundup Ready soybean cultivars (n=8) (% of trial mean yield, n=57 cultivars) adapted to the 2900-3300 heat unit zone (from 1999 Report Ontario Soybean Variety Trials, Table 4)

Variety Designation Clay Soil Loam Soil Proprietor
Dutton Inwood Ridgetown Talbotville
AG1901 100 99 96 102 Cargill
AG2101 102 99 100 104 First Line
PS86RR 102 98 96 99 Pride
S20-B9 91 94 93 90 Novartis
RR Renown 99 98 95 102 Hyland
AG2301 95 100 100 95 First Line
3101R 93 96 103 99 First Line
MEAN 97 98 98 99  
bu/ac 52.3 54.3 62.9 62.1  

3. When are they going to get it right? The evolution of pest resistance to Bt is a foregone conclusion, as virtually everybody will admit. Pesticidal plants like Bt-corn are no different than DDT or atrazine - insects and diseases, and to a lesser extent weeds, are extremely well adapted to evolve resistance whenever faced with a powerful and efficient "screen" - like tens of millions of hectares of cropland all expressing the same toxin.

The only source of contention among scientists is "when" and how to delay resistance. The high dose/refugia model which has been widely promoted by both industry and government proponents was supposed to be the best available strategy to forestall resistance, but you may have noticed that the size of the recommended set-aside has increased just about every year. When Bt hybrids first came out, producers were told to hold back a 5% refugia (to plant to a non-Bt hybrid). Then it was 10%, and now it is most commonly recommended as 20% (plan submitted to the US EPA by Monsanto, Mycogen, Dow Agrosciences, Novartis, and Pioneer Hi-Bred; AgNews, 23 Apr 99; also by the Bt Corn Coalition to the Plant Biotechnology Office of the CFIA in October 1998), although some are calling for 40%. Why the confusion? Why is the figure changing - and always upwards?

The confusion is caused because those promoting refugia as the best solution have not done their homework. This is a clear example of a general and pervasive problem with agricultural biotechnology - namely, technology has preceded science. Ag biotech has been released prematurely, for reasons of profit, before the scientific evidence has been developed. Proponents, and the researchers in their employ, did not take the time to answer some of the key questions regarding the effectiveness of refugia in restricting evolution of cornborer resistance.

And unfortunately for proponents of this model, many of these untested assumptions have now been challenged by recent research published in the most prestigious journals. What we now know is that the high dose/refugia model is unlikely to work, at least for cornborer.

Table 3. Key assumptions of the "high dose-refugia" model of resistance management.

No. Assumption Evidence to the Contrary
1 Major resistance genes must be very rare In diamondback moth, one of eight species that have already evolved resistance to Bt, Tabashnik et al. (1997) showed that resistance is not rare - its actually 10X higher than the highest previous estimate
2. Resistance genes must be nearly recessive According to Huang et al. (1999), resistance in ECB is dominant, while in other pest lepidopteran species, resistance varies from recessive to incompletely dominant. Furthermore, resistance varies not only among species, but also among types of Bt endotoxins, e.g. CryIAc, CryIAb, CryIIA
3. Non-Bt refuges must provide susceptible pests to mate with resistant ones; requires random mating and suitable dispersal distances Cornborers consuming Bt (and living) typically suffer delayed development, which causes them to reach reproductive maturity out of phase with their neighbors in the refugia. They won't be able to mate anyway.

4. Do the GE crops, in fact, do what is promised? Reduce production costs? Reduce pesticide applications? Increase yield? Increase profit?

Costs and profits are a hard issue to address in the abstract, as much varies with weed and insect pest pressure and other farm-specific issues. Yield is already known to be lower - or at best, no better - than conventionally bred crops. But what about insecticide use? If you use Bt, then you don't need to use insecticides, right? And that protects both you and the environment, and that's good, right?

Indeed, Monsanto made just such a claim in a press release dated 21 May 99, in response to recent research showing an adverse effect of Bt pollen on Monarch butterflies (see below). Monsanto stated:

"In 1998 use of Bt insect-protected corn reduced or eliminated the use of broad spectrum chemical insecticides on some 15 million acres of US farmland".

Now, that would be a pretty impressive achievement, if it were true. So, let's see - some 71.4 million acres of corn were grown in the US in 1998, and data from the USDA National Agricultural Statistics Service (http://www.usda.gov/nass/pubs/rptscal.htm, courtesy Chuck Benbrook, personal communication) shows