Canadian wheat producers should escape the Hessian fly problems that their counterparts in the southeastern United States are encountering, says a Canadian expert.
Many of the genes in the winter wheat varieties grown in that region of the U.S. have lost their effectiveness in warding off the insect.
Scientists with the U.S. Department of Agriculture and Purdue University say farmers should exercise care to ensure resistance genes that have not yet been used in commercial lines are used prudently.
“The number of genes available to protect wheat is limited,” said Richard Shukle, a USDA research scientist and associate professor of entomology at Purdue.
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A recent study by a colleague at Purdue indicated only five of 21 genes evaluated would provide effective resistance to the flies in the southeast and none were effective in all 20 testing locations from North Carolina to Louisiana.
The pest can cause millions of dollars in damage a year in the southern U.S.
Ian Wise, an entomologist at the Cereal Research Centre in Winnipeg, said several factors allow Canadian producers to escape significant Hessian fly damage:
• unfavourable timing of the susceptible crop stage and the Hessian’s flight period;
• high levels of parasites that provide control;
• none of the resistance genes used in the U.S. wheat are present in the Canadian varieties.
“All of our Hessian fly populations are avirulent (not susceptible to damage) to all these genes,” said Wise.
Proper crop rotations that take wheat genetics into account provides a measure of control, but it’s also becoming less effective over time, he said.
Wheat resistance genes recognize avirulent Hessian flies and activate a defence response that kills fly larvae attacking the plant.
However, over time this results in new strains of the fly that can overcome resistant wheat, similar to pesticide resistance.
One suggestion has been to stack genes in a wheat cultivar.
“We can’t afford to release wheat lines with only one resistance gene,” said Shukle.
“If you deploy two different resistance genes, it’s unlikely that a population of flies could overcome both of them.”
Wise said some of the resistance genes that are no longer effective in the U.S. could work in Canada, where Hessian fly pressure isn’t as heavy.
Hessian flies, in the same family as wheat midge, can show up anywhere in the Prairies and are usually associated with late-seeded wheat.
No control products are suitable for spring wheat, but disulfoton is effective on winter wheat.
Hessian fly larvae feed on the plant at the point where the leaf blade meets the stem. This weakens the stem, predisposing it to breakage and yield loss.
There are two generations a year. In winter wheat, the emergence of flies is triggered by fall rain. The flies lay eggs and establish the new generation that causes feeding damage to seedlings.
A second generation emerges the following spring.
