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Sawfly cuts across Prairie wheat acreage, spurs research to rescue

Wheat biologist Brian Beres remembers the first time he witnessed the devastation of the wheat stem sawfly. There was no sign of damage, no hint of the pest. Then the wind blew.

“We went out to this field in Southern Alberta. The producer was gearing up to go in and combine at the beginning of the week, when a severe windstorm hit over the weekend and toppled everything that was cut or girdled by sawflies. It was quite a sight – his whole field was about 90 percent cut,” says Beres.

That was three years ago, in a relatively isolated case. But this year producers are seeing the high-water mark in a rising tide of sawfly damage across the Prairies. Early estimates put the level of sawfly-toppled wheat at 30 to 50 percent in at-risk areas throughout the heart of wheat country, with some fields experiencing over 75 percent cutting.

The increasing damage and lack of control options has spurred a beefed-up research effort from scientists across the Prairies. Farmers are supporting this research through the Wheat Check-off Fund administered by Western Grains Research Foundation.

The major research effort to breed sawfly-resistant wheat varieties is led by Dr. Ron DePauw and Dr. Fran Clarke of Agriculture and Agri-Food Canada’s (AAFC) Semi-Arid Prairie Research Centre in Swift Current and Dr. Taing Aung of the AAFC’s Cereal Research Centre in Winnipeg.

The focus of this effort is to develop solid-stemmed wheat varieties, says DePauw, head wheat breeder. “Female sawfly insert their eggs into the hollow stem of the wheat plant, and the damage is caused by the larvae that develops inside the stem. By developing wheat with higher stem solidness, we can prevent the sawfly from inserting eggs and reduce the chance of larval survival.”

Already an important variety developed by DePauw’s team, AC Abbey, is getting out to producers. The variety was registered in 1998 and seed will be widely available in 2002. “AC Abbey is not immune, but it helps reduce the sawfly population,” says DePauw. Though this variety does not have a high degree of stem solidness, it has enough resistance to significantly reduce sawfly damage by over 50 percent compared to hollow-stemmed wheat.

A drawback is that AC Abbey produces up to 0.8 percent lower protein than newer hollow-stemmed wheat such as AC Barrie. Older solid-stemmed varieties such as AC Eatonia are also available, but carry a large yield penalty. “Traditionally, the solid-stemmed wheats have not yielded as well as the hollow-stemmed wheats – so there’s an economic disadvantage to producers,” says DePauw.

The researchers plan to overcome those obstacles. Several potential successors to AC Abbey are in development, with higher sawfly resistance and a better quality package. The first of these is expected to be up for registration in two or three years.

In the meantime, farmers should take steps to reduce their risk. Brian Beres of AAFC’s Lethbridge Research Centre leads a multi-disciplinary sawfly study that includes a strong risk management component. It involves Lethbridge entomologists Dr. Hector Carcamo and Dr. Bob Byers, along with DePauw and Clarke. This study is supported in part by AAFC Matching Investment Initiative funds matched to the Wheat Check-off Fund.

“Since sawfly overwinter in the previous year’s stubble, producers should expect high numbers again in 2002,” says Beres. “Our goal last year, once we had compiled some preliminary results in September, was to deliver the message to producers that the wheat stem sawfly was back and producers in areas prone to attack should brace themselves for a heavy infestation of sawfly in 2001. The same message will be delivered for 2002.”

Aside from shifting away from wheat or tight wheat rotations, the best defense is to plant solid-stemmed varieties from a certified seed source, says Beres. One option is to seed the perimeter of the field to solid-stemmed varieties, while seeding the inside to a high-performing variety (it’s important both varieties are eligible for grades of the same class.) The sawfly is a weak flier and can often be confined to the outer 30-60 feet of wheat fields. “Trap cropping can be a good compromise to offset yield losses, but in high risk years such as this one, the sawfly populations are so high they often go far beyond that perimeter,” he says.

The sawfly is an old wheat problem that had tapered off before this past upward swing in the population, and it will likely die down again eventually, he says. In recent years, the dry weather cycle, conservation tillage systems and tight wheat rotations using hollow-stemmed varieties likely contributed to the current outbreak.

The farmer funded and directed Wheat Check-off Fund allocates approximately $3 million annually to variety development research.

WGRF information at www.westerngrains.com

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