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Wednesday, 14 December 2011 15:20

Lethbridge Research Centre trying to clip the wings of sawfly

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By Jamie Woodford — This email address is being protected from spambots. You need JavaScript enabled to view it.

The Wheat Stem Sawfly (WSS) is a serious cereal pest.


One female sawfly can carry as many as 50 eggs which it releases into the stems of wheat that the larvae tunnel through.

When they emerge as an adult, the flies damage the base of the stem causing it to fall to the ground. The result is lower yields not only from stem boring, but also in trying to recover the fallen stems come harvest.

The drier areas of southeast Alberta and southwest Saskatchewan are “hot spots” for the native pest that have been around since the 1800s, but after collecting more than 10 years of data, scientists have created an effective management strategy to keep the pest at bay.

Cereal agronomist Dr. Brian Beres and insect pest management researcher Dr. Héctor Cárcamo of the Lethbridge Research Centre, have developed a plan for successfully managing the pest that “requires a complex approach integrating host plant resistance, agronomic and biological control strategies.”

The threat of WSS is not as bad today as it was just a few years ago. An outbreak in 2000 reminded wheat growers and researchers that consistent monitoring and pest management needs to be a priority.

“It was quite devastating. It was quite honestly surreal,” said Beres of the outbreak.

“There was just oceans of wheat just down, and it was hitting everywhere — eastern Alberta through down to southern Alberta, and then the drought kind of made its way into Saskatchewan and so did this major outbreak.”

He estimated about 100 million hectares were affected annually.

“Generally you’re going to lose about 30 per cent of your attainable grain yield. In the prairies, it was probably around 150 million (hectares) at its peak,” he said.

One of the problems with sawfly is that it’s immune to insecticides.

“The biology of the sawfly is such that you can’t really intervene with a chemical like you can with grasshoppers. Their flight period is so short when they’re outside the stem that you can’t kill them when they’re in flight, and we probably don’t want anything that’s systemic enough on a seed at planting that would remain in the plant til June to kill the larvae that’s inside,” he said.

Thanks to cooler, wetter springs the WSS epidemic subsided, but wheat fields are not out of the woods yet.

“Once we get some dry weather again, that could change awfully fast,” he said, which is why releasing the strategy now is important so farmers can start planning.

The strategy focuses on six areas: pest surveillance and monitoring; pre-seed residue management; cultivar selection; cropping system; nitrogen management; and harvest management and bio-control.

“I started at activities before seeding, during seeding and at harvest, that we could do that would either manage our risk in a sawfly environment or conserve those biocontrol for natural enemies of sawflies,” Beres explained. “Basically, we just took the results of our studies and then I came up with this sort of schematic of what I thought would be a good idea in terms of managing.

“My point here was that pest surveillance should be the over arching thought to get the rest of these ideas flowing,” he said.

“Then, just follow it up with what I thought were components of a good integrated pest or crop management system for it.”

Risk maps are used to determine what type of threat is expected in a particular area.

“Then, that could be followed later up in the year with in-crop assessments,” he said. “You could determine your risk by going for a walk in your fields splitting some stems, and if you find some of those guys cuddling inside — if there’s more than say two to four out of every 10 stems that you split, that’s getting to be a moderate threat. Anything more than that would be a high threat.”

Once it’s determined whether a field is a low to moderate threat or a moderate to high threat of infestation, farmers can use the strategy provided in each of the five areas to decide on the next course of action.

“In the back of my mind as a producer, I would want to be thinking I’m probably going to have to adjust my practices at harvest so that instead of encountering all these stems flat on the ground, it may be think about things like swathing ahead of combining,” he said.

Sawfly management should not be about eradication, said Beres.

“What it should be about is a sort of peaceful co-existence where you’ve taken a threat that’s high and you’re managing it so that it’s relatively low when you are growing your wheat. I think that’s do-able if you can as much as possible think about each area and each component and do your best to integrate it and if you can do that, that’s when things like harvesting at a higher height in the fall helps.”

The research was conducted in collaboration with scientists at the Lethbridge Research Centre, the University of Alberta, Montana State University, and Alberta Agriculture and Rural Development.

Articles on this research is publicly available from journal websites Agronomy Journal (Vol. 103, Issue 6; https://www.agronomy.org/publications/aj/new-articles) and Prairie Soils and Crops Journal (Vol. 4, 2011; www.prairiesoilsandcrops.ca).


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