Wheat Stem Sawfly Widespread

REGINA - Feb 2/04 - SNS -- The first survey in 40 years of wheat stem sawfly populations reveals most wheat growing areas in Saskatchewan will face problems with the pest this year.

"Sawfly is definitely going to be out there in 2004," says Dr. Owen Olfert, a research scientist with Agriculture and Agri-Food Canada in Saskatoon. "There is no insecticide for sawfly, so producers should be aware of their options now, because many of these options require pre-planning."

Olfert says the area of infestation follows the boundaries of the Palliser Triangle and extends into the Dark Brown Soil Zone and Parkland. In eco-region terms, this means sawfly populations are found in the mixed grassland, moist mixed grassland and aspen parkland regions.

The insect control specialist with Saskatchewan Agriculture, Food and Rural Revitalization (SAFRR), Scott Hartley, says the 2003 sawfly survey shows that the insect is not restricted to south Saskatchewan. It also corrects any misconception that sawfly is only found in the margins of the field.

"Historically, there has been an edge effect, with more sawfly in the field margins than in the inner parts of the field. But, with this latest resurgence, sawfly is often found throughout fields."

Still, Hartley says, the survey sampled two parts of the fields - near the edge and 100 meters into the field - and, while the results show areas where it is widespread, the edge populations were significantly higher in a number of pockets throughout the province, particularly in the Lucky Lake area.

One of the reasons for the 2003 survey, carried out by the federal and provincial agriculture departments, was the reports from farmers about increased numbers of wheat stem sawfly starting about 1999. Thought to be native to North America, sawfly was considered an agricultural pest by the early 20th century but, partly because of the introduction of a sawfly-resistant, solid-stem wheat variety, became a lesser problem for a number of years.

"This resistant variety, Rescue, was solid stemmed and solved the problem in the affected areas. With the decline in sawfly populations, farmers started growing varieties with higher yields but no resistance, so they were caught by surprise. Fortunately, wheat breeders had produced newer resistant varieties - the solid-stem AC Eatonia and AC Abbey - that had higher yields and quality than Rescue. Under pressure, these varieties are not 100 per cent resistant but they are better than hollow-stem varieties," says Olfert.

One of the ways of dealing with the wheat stem sawfly is by returning to these solid-stem varieties, which are generally effective because the larva cannot cut their stems. It is this cut that weakens the stem so it falls over easily, making harvest difficult and thus lowering yields. Sawfly feeding on the inside of the hollow-stem varieties also affects the transfer of nutrients to the head, resulting in an overall reduction in the number of seeds per head and a corresponding yield decrease.

Because the preferred hosts for the wheat stem sawfly are spring and durum wheat, with rye, triticale and even barley sometimes affected, the most effective way to avoid sawfly damage is to grow oats and broadleaf crops such as canola, flax and alfalfa. If wheat is to be grown as a part of a current rotation, solid stem varieties should be grown. Hartley reminds farmers that AC Abbey has good yields, AC Eatonia has good protein, and both tend to better withstand the drought conditions that often coincide with sawfly outbreaks.

"If damage in the previous year is confined to the field edges and has reached 10 to 15 per cent stems cut, resistant varieties could be seeded around the perimeter of the field as a trap or barrier crop, with a high-performing conventional variety in the remainder of the field. If damage extends across the field in the previous year, the whole field should be seeded with a resistant or non-susceptible crop," says Hartley.

Olfert says the 2003 survey showed several areas of the province had fields with at least 10 cut stems per meter, which is the level at which economic loss occurs. If farmers discover this level of infestation during the 2004 season, he says, they should harvest earlier if possible, or swath with the cutting bar lower than usual.

Dry weather cycles and tight wheat rotations are the primary factors contributing to increased sawfly populations. The 2003 Wheat Stem Sawfly maps will indicate to farmers the potential for losses in these areas. SAFRR's "Wheat Stem Sawfly" factsheet will tell them how to deal with it.

The "Wheat Stem Sawfly" factsheet is available on SAFRR's Web site. Those without Internet access may have the factsheet printed at the nearest rural service center.

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