Bt Corn and Resistance Management
Abridged
from an article by Sandra Lastovic, University of Guelph, M.Sc. student
To better understand producer attitudes about Bt corn and what types of resistance management strategies farmers
would be willing to implement when growing Bt corn, the University of Guelph – in co-operation with the OCPA –
surveyed commercial corn producers in Ontario during April 1998. A synopsis of results from over 800 responses
is discussed here.
Perceived damage caused by the European Corn Borer (ECB)
Although the severity of corn borer pressure cannot be accurately
predicted from year to year, most farmers (91.3 per cent) think that the ECB can cause serious economic yield losses
in field corn. These growers perceived an average yield loss of 20 bushels per acre. This differed from the actual
yield loss in Ontario, which averaged 11 bushels per acre for the 1998 growing season.
Although the majority (79.4 per cent) of corn producers reported scouting for corn borer (a recommended action
when using Bt hybrids), it’s questionable if they knew when to or even how to scout, considering 32 per cent of
respondents were not certain of the number of ECB life-cycles in their fields. Those farmers who perceived that
corn borer could cause severe economic yield losses, however, were also more likely to personally scout their fields.
Farmers’ perceptions on how Bt corn will influence ECB
control
When asked if any controversy within the general public over
biotechnology would influence their decision to use Bt corn, 13.7 per cent of respondents said that this issue
would be extremely important, and 37.4 per cent indicated that it would be moderately important. Greater than 85
per cent of respondents said ‘yes’ when asked if they considered Bt corn to be “biotechnology.”
The results of this study indicate nearly 55 per cent of Ontario growers planned to plant Bt corn in 1998. Growers
who had used Bt corn in the past were primarily doing so to personally evaluate the Bt technology (68 per cent).
Usually, farmers think corn borer can cause serious economic yield losses were significantly more likely to plant
Bt corn in 1998. In general, farmers who had made a conscious effort to control ECB in the past (i.e., harvesting
early and using tolerant hybrids) were
Often a key deciding factor in utilizing a new technology on the farm
is economic advantage. Producers living in regions of Ontario with typically more than one generation of ECB per
growing season perceived greater corn borer-related yield loss than those who live in single-generation areas.
This could result in concentrated areas of heavy Bt corn use; in these areas there is a greater need to adhere
to resistance management strategies.
Significant yield increases and cost were rated by the majority of respondents as extremely important in their
decision whether to use Bt corn. Yet farmers who had used Bt corn rated their results on these criteria unfavourably.
In fact, only 15.2 per cent of Bt corn users in 1997 said they strongly agreed to having noticed a significant
yield increase when using Bt corn. On cost effectiveness, 30.1 per cent responded that the cost of Bt was acceptable,
whereas 32.5 per cent responded that the price was “a little too high” and 25.6 per cent responded that the price
was “too high”. The implication is that the economic advantages of Bt corn may have been oversold.
Farmers’ perceptions of insect resistance management (IRM)
strategies
The foundation of IRM to delay resistance to Bt corn relies on
refuge and high-dose strategies. Refuge refers to planting a portion of each field with non-Bt hybrids to allow
for interbreeding between corn borers which may have developed resistance and insects that are susceptible to Bt.
High dose refers to the fact that the level of Bt toxin in the crop is 25 times the toxic concentration needed
to kill susceptible larvae.
Almost half of the respondents think that it’s extremely possible for the ECB to become resistant to the Bt toxin
in Bt corn. However, 40 per cent of producers think that it is only somewhat possible for ECB to develop resistance
to the Bt toxin. Since a large proportion of producers are not fully convinced the ECB will develop resistance,
persuading Bt corn growers in Ontario to implement IRM strategies may be difficult. Nevertheless, farmers who think
ECB will develop resistance were also more likely to agree that using resistance management practices was important
and that it should be done on their own farms.
However, the knowledge on how to implement IRM practices is weak. Moreover, scientific uncertainty has translated
into uncertainty at the grower level. Nearly half of the respondents (41.2 per cent) said that although they have
heard of a Bt-IRM strategy, they disagree this method (refuge/high dose strategy) will be effective in preventing
resistance. Interestingly, those farmers who had heard of IRM practices to prevent Bt resistance more likely to
think the ECB will inevitably develop resistance. This attitude may limit farm level implementation of IRM strategies,
if the farmers’ belief is that because resistance is inevitable, there is no immediate reason to spend valuable
time and money.
Another impediment to implementing IRM in Bt corn may be producer attitudes towards alternative products that will
control resistant insects in the future. Not surprisingly, 73.6 per cent of all respondents answered that they
‘agreed to some extent’ that companies will have new products for them to use should ECB resistance occur. For
example variations of the Bt toxin, such as the Cry9C strain, will soon be available. This product has been positioned
as an alternative to Cry1A, the only Bt toxin currently available in Ontario Bt corn. Although Cry9C has a different
mode of action, there is no assurance against the possibility of cross-resistance, a reality that would have serious
implications for ECB control.
IRM strategies growers will consider implementing
When asked to specify in their own words what type of resistance
management strategy respondents had heard of, 42.2 per cent answered “plant some non-Bt corn”, although answers
were very general as to what constituted effective IRM strategies.
The planting methods most preferred by farmers were alternating every row or several rows with Bt and non-Bt corn
(15.2 per cent), and planting Bt corn as a block in each field (15.4 per cent). Nearly one quarter of the respondents
did not know what planting pattern they would most likely consider. Repeat users of Bt corn were generally more
aware of what types of effective IRM strategies are required, and prefer planting refuge in large strips more than
other planting patterns.
Nearly 30 per cent of the respondents were willing to plant 41-50 per cent refuge to delay resistance, whereas
about one quarter of producers did not know the per cent of acres that they would be willing to plant to non-Bt
corn.
Although Ontario corn producers are generally aware of the potential for Bt resistance and think resistance management
strategies are important, there is a discrepancy between what is required for IRM and what growers are willing
to consider doing. If growers do not understand what type of planting pattern is appropriate, they are unlikely
to implement IRM strategies on their farm, even if they feel it is important. Growers are primarily economically
motivated, and there is little immediate economic benefit to implementing IRM strategies. In some cases, growers
may feel that by planting a refuge they are limiting the profitability of using the technology.
Resistance Management and the Role of Information Providers
Several companies who sell Bt hybrids require growers to sign
contracts when they purchase Bt corn to confirm their responsibility to implement IRM strategies. However, growers
do not bear the entire burden for the responsible deployment of the Bt technology. The Ontario Corn Borer Coalition
recognizes that all individuals and institutions in Canada involved with Bt technology are responsible for the
proper stewardship of the technology. As well, the research and extension community accepts the responsibility
to provide timely communication of scientifically based information about using Bt technology to the seed industry
and to corn producers.
The survey results show the top three sources of information that were extremely important to growers in their
decision to use (or not to use) IRM strategies were: seed dealers (40.4 per cent), university field trials (38.3
per cent), and company reps (26.7 per cent). Farm magazine articles (a mass medium) were rated lower in importance
than interpersonal information sources. Overall, there was a need indicated for information sources to better
address the information requirements of producers. It is likely producers judge the accuracy, balance and fairness
of the IRM information on content and on the reputation of the source and the legitimacy of the processes by which
recommendations were developed. The survey results highlight important considerations for the Ontario Corn Borer
Coalition in implementing IRM recommendations.
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