Saskatchewan Wheat Stem Sawfly Outlook Bad

REGINA - Mar 19/03 - SNS -- The number of options available to Saskatchewan producers who want to plant a crop which will not be ruined by insects or disease this season is shrinking.

While some specialty crop companies are looking for growers to move land from lentils to wheat because of worries about grasshopper outbreaks, provincial agriculture officials are warning growers to consider alternatives to wheat because of the high risk of severe outbreaks of wheat stem sawfly this year.

Scott Hartley, insect control specialist, Saskatchewan Agriculture, Food and Rural Revitalization, says, "There are no effective or registered insecticides for wheat stem sawfly, so producers who experienced damage greater than 10% to 15% of last year's wheat crop must use other strategies to manage this pest. The most effective way to reduce damage from the wheat stem sawfly is to plant resistant crops in a rotation. Barley and oats tend to be resistant, while broadleaf crops such as canola, flax, alfalfa and pulse crops are considered immune."

If it is necessary to grow wheat as part of the current rotation, solid-stem varieties should be chosen. AC Abbey and AC Eatonia appear to have the best resistance, but Hartley emphasizes that they are resistant, not immune, to sawfly damage. Under severe sawfly pressure, even solid-stem varieties can be cut by this pest, though to a lesser degree than hollow-stem varieties.

"The production of solid stems by AC Abbey and AC Eatonia is variable from year to year, as it is influenced by environmental conditions and possibly soil type. This means that the resistance of these varieties can vary from year to year. Producers should note that seed supplies of AC Abbey and AC Eatonia continue to be limited."

Hartley says winter wheat has been recorded as a major sawfly host in Montana, where producers now consider sawfly to be the number-one insect problem in the state. Winter wheat, to some degree, has become a sawfly host in southern Alberta as well. Recent trials with durum wheat have shown that some varieties appear to be more affected than Canada Western Red Spring (CWRS) wheat.

"Solid-stem wheat varieties, oats or barley can also be planted as a border/trap, with a conventional hollow-stem variety inside the field, but this strategy is only feasible if the previous year's damage was confined to the field margins. If two different wheat varieties are seeded, it is important that both varieties are eligible for grades of the same class: for example, if the border is seeded to CWRS wheat AC Abbey, the inside of the field should be seeded to another CWRS wheat such as AC Barrie. Other factors, such as maturity and height, should also be considered if the varieties are to be harvested together."

Damage by the wheat stem sawfly is done after the adult female lays its eggs in the plant stem. Although feeding within the stem during the course of the season will result in reduced seed set and shrivelled seeds, the greatest damage occurs when the larvae eventually burrow downward and cut a V-shaped groove around the inside of the stem about one inch above the soil surface. This weakens the stem and the plant falls over, making harvest difficult. But the females will not lay their eggs before elongation of the stem occurs, or after the boot stage. The timing of these stages is determined by the planting date, but also by environmental conditions.

If field scouting has identified sawfly infestations, one option is to swath the affected fields as soon as possible to avoid lodging, generally as soon as the kernel moisture drops below 40%.

"All these management strategies should be applied over the long term because several years are needed to reduce sawfly populations," says Hartley.

One strategy that is not recommended is the mowing or burning of ditches and field edges. These areas may harbor the pest but they are also home to the natural enemies of the wheat stem sawfly, such as the parasitic wasp. It has been shown that the parasites over-winter higher in the stem than the sawfly so, to assist parasite populations, a current research project is considering optimal cutting height during harvest. Other research has shown that a bio-chemical produced by plants is an attractant to the wheat stem sawfly; the production of this biochemical differs among varieties, which may account for the variability in cutting by the sawfly among hollow-stem wheat varieties.

The Agriculture and Agri-Food Canada Research Centre at Swift Current continues to breed sawfly resistance in both spring wheat and durum. Current varieties have been bred from a single source of the solid stem trait in spring wheat, but breeders now have a second source for this trait. One promising line, which has greater solidness and a seven% higher yield than AC Abbey, has been submitted for registration.

Because of the return of the wheat stem sawfly as a major pest of spring and winter wheat in extensive regions of Saskatchewan, Alberta and Montana, the International Sawfly Working Group was formed in late 2002. It is hoped that the collaboration of researchers and two levels of government in Canada and the United States will result in the development of practical management methods without the duplication of resources.

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