Alberta’s alfalfa bug survey yields mixed results in first year

News Roundup from the June 2015 issue of Canadian Cattlemen

One concern is the increasing spread of alfalfa weevil.

Year one of a three-year benchmark insect survey across Alberta yielded mostly good news and a few surprises, even for Alberta Agriculture entomologist Scott Meers of Brooks who is heading up the project.

The biggest surprise was the sheer abundance of life in alfalfa fields. Sweep net samples of 100 sweeps each captured several thousand insects. The highest count was over 10,000 in one sample.

As alarming as that number may sound, most of the insects were neutral or beneficial to the alfalfa. They found lots of little moths, thrips, mites, ladybird beetles, and even a weevil that attacks dandelion seed that has been sent away to the Agriculture Canada’s National Identification Services in Ottawa for identification.

No new problem insects were detected in the 150 mixed-alfalfa fields sampled across the province last year.

One concern was the change in intensity and range of the alfalfa weevil. A lot of these pests were found in southern Alberta where the insect traditionally has been an issue, however, they also found fields facing serious weevil pressure around Stettler and the foothills around Calgary.

Generally, the first phone calls Meers gets about weevils come in after the first cut when worried producers notice significant leaf loss or poor regrowth.

The weevil isn’t much of a problem for dairy producers because they cut alfalfa early ahead of the buildup in weevil numbers.

The Alberta survey mirrors the alfalfa insect surveys done in Saskatchewan from 2010 to 2012 so the findings will be comparable. In Saskatchewan they found alfalfa weevils went from an occasional forage pest in 2010 to a major one spread right across the province by 2012.

The western strain of the weevil was first discovered in southwestern Saskatchewan and southeastern Alberta in 1954 where it remained for 40 years before starting to advance eastward into Manitoba. (See Canadian Cattlemen, April 2013, for more on the Saskatchewan survey and weevil control measures.)

Another pest of interest is the alfalfa blotch leafminer. This small black fly slowly migrated from Eastern Canada, where it’s been well established since the 1970s, into Manitoba by the mid-1990s. Its spread westward since then has been more like a jump with it detected both in Regina and Brooks, Alberta in 2005.

The adult fly produces three generations in a growing season. Meers says two, possibly three, species of leafminer can be found in Alberta. Up to now, he says, a local parasitic wasp has kept populations below the economic threshold. The three-year survey will show how it has spread and the location of the different species.

There weren’t any surprises in terms of lygus and alfalfa plant bugs.

Part of this year’s field work will follow lygus in alfalfa and canola to determine whether there is a connection. For instance, if a canola field is cut, will the bugs move into alfalfa? Previous studies say no, but there may be other connections.

The alfalfa-canola lygus project is separate from the benchmarking of 100 as-pure-as-possible alfalfa fields this summer and another 100 in 2016. That averages out to one field per county and two in counties with the most alfalfa and alfalfa insect pressure.

“You never know what you’ll find until you really look,” says Meers.

As far back as records go, there has never been a comprehensive survey of alfalfa insects in Alberta. The project is being funded by the Western Grains Foundation and the Alberta Crop Industry Development Fund.

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