Manitoba corn growers are the luckiest in North America when it comes to dealing with bugs: many insects can’t hack the weather.
And that’s why Bt corn can be used most aggressively in the Great White North: there’s no need to leave more than a 20 percent refuge zone for pests.
Which is why producers shouldn’t try to push that 20 percent lower, says Manitoba Agriculture pest specialist, Brent Elliott. Bt corn works so well that it would be a tragedy to destroy its effectiveness.
“At some time down the line there will be resistance. It’s like any pesticide. It’s not a question of if. It’s a question of when,” said Elliott.
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“Hopefully it won’t be for a long time.”
Bt corn almost eradicates the damage caused by corn borer, a key pest of corn. The genetically modified crop produces the same substance as a soil borne bacteria that some bugs can’t digest, so when the bugs eat the corn, they die of indigestion.
Bt crops’ effectiveness is ironically undermined by their success: producers like the crops so much that they will seed everything they can with it. But that creates evolutionary pressure on bugs to become resistant to the effect of Bt. If only a few bugs that can survive after eating Bt crops live on and multiply a new generation of Bt resistant bugs will be born.
To eliminate that threat, agronomists say producers in Western Canada should put about 20 percent of their corn acreage into non-Bt varieties. That way there will be a reservoir of non-Bt resistant bugs to breed with the resistant bugs in the other fields, and the resistance problem will be minimized.
The 20 percent recommendation stands for fields that will not be sprayed with any other insecticides. If a producer is also planning to use insecticides, he should be leaving 40 percent in non-Bt varieties.
U.S. farmers often have far more bug pressure to deal with, including bugs that are not susceptible to Bt.
“In Manitoba we don’t have all of those pests,” said Elliott.
“We’re getting a good bang for the buck.”
Elliott said Bt corn isn’t always a necessary investment.
The premium on Bt varieties costs about the same as a single spraying of insecticide on a crop, so if bug pressure is going to be lower than the spraying threshold, it might be better to seed a cheaper corn.
But since it is almost impossible to tell whether corn borer will be a pest in any particular year, using Bt corn has become a key risk minimization strategy for many growers.
“Most people view it as an additional form of insurance,” said Elliott.
“If you have a moderate to high corn borer population it’s a no-brainer. It works really, really well and you’ll get your money back out of it.”
