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Old pests and emerging insect problems

Some pest problems were up in 2009, while others were down. And there are a few new ones to keep an eye on in 2010.


April 30, 2010
By Bruce Barker
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The cereal leaf beetle feeds on the leaf tissue, leaving semi-transparent strips on leaves. Photo by Bruce Barker.  

Some pest problems were up in 2009, while others were down. And there are a few new ones to keep an eye on in 2010.

Emerging pests to watch
The cereal leaf beetle is working its way across the Prairies.  It was first seen in Alberta in 2005, observed in Saskatchewan in 2008 in the southwest corner, and identified in northwest Manitoba in 2009. John Gavloski, an entomologist with Manitoba Agriculture, Food and Rural Initiatives, says that while the arrival of the cereal leaf beetle was not unexpected, he was surprised where it was found. “Both the Canadian Food Inspection Agency and Manitoba Agriculture, Food and Rural Initiatives have been surveying quite intensively for years, with increased focus along the border with North Dakota. But the beetles, mainly larvae, were found near Swan River, north of where we were focusing our scouting,” says Gavloski. 

When the cereal leaf beetle was observed at Swan River, 12 fields were surveyed and 18 larvae were found in four of 12 fields. “Those aren’t big numbers. If we weren’t looking for the insect, it would have been hard to see, and the damage was insignificant in the area,” says Gavloski.
These cereal leaf beetle larvae were sent to Alberta to be examined for a parasitoid that can be very effective at reducing levels of cereal leaf beetles; but no parasitoids were found.

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In Alberta, Scott Meers, insect management specialist with Alberta Agriculture and Rural Development, says that the cereal leaf beetle numbers continue to increase in surveys conducted in 2009. While populations remain low and economic damage to cereal crops remains variable, the surveys have found that the beetle continues to disperse over an increasingly large area. The most severe infestation was seen in a barley field near Taber, Alberta. Meers says that the parasitoid Tetrastichus julis has established in southern Alberta, and appears to be moving with the cereal leaf beetle populations. 

Saskatchewan Ministry of Agriculture insect specialist Scott Hartley says that the cereal leaf beetle is in southwest Saskatchewan. “We know it is there, but the numbers are low so it is not a big concern at this point.” He says that researchers and entomologists are keeping an eye on the insect, but do not know when or if it will become an economic pest.

The swede midge is another emerging pest to watch. It was found at three locations in Saskatchewan in 2007, and at two sites in 2008 in Manitoba near Glenlea and Portage la Prairie. The swede midge feeds on cruciferous crops, and damage to a young plant prior to stem elongation can result in lack of raceme, flower or pod production. Injury to plants that have bolted already results in all the pods forming at the injury site, causing a bouquet of pods, although yield is typically not impacted in this case.

Gavloski cautions that there are other causes for a bouquet-type injury, including lygus bug or abiotic injury, to the growing tip of the developing flower head.

Meers says that the swede midge has not been found in Alberta although Canola Council of Canada photographs are strongly suggestive of an infestation in central Alberta in 2009 near Vegreville. Plans are underway to monitor the site in 2010 with pheromone traps.

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 Scalloped notches signal the presence of the pea leaf weevil.  
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Swede midge can cause a bouquet-type injury to canola.
Photo courtesy of Canola Council of Canada


 

The cabbage seedpod weevil was first discovered in Alberta in 1995 and in Saskatchewan in 2000. It is not currently known to be in Manitoba. In southern Alberta, Meers says the weevil is a perennial concern, and spraying is routine south of the Trans-Canada Highway.

In Saskatchewan, Hartley says that the cabbage seedpod weevil also has continued to expand east and north from the southwest corner of the province. Although the main economic infestations are still reported in southwest Saskatchewan, surveys have found weevils near Regina and Saskatoon in 2009.

The cabbage seedpod weevil appears to be increasing its range in Western Canada to the north and east at a rate of about 60 kilometres (38 miles) per year. The larvae feeding on developing seeds inside the seed pods cause the main economic damage. Gavloski says that if growers find weevils and they are not sure of the identification, to consult with agronomists to help with identification. He says there is another weevil that can be found in canola, but its preferred host is flixweed and it should remain a minor concern in canola.

Meers says that environmental conditions in southern Alberta were favourable for cabbage seedpod weevil in 2009, so the insect is expected to be a potentially severe problem in 2010.
The pea leaf weevil is primarily a pest of pea crops and continues to cause problems on the southern Prairies. In Alberta, the 2009 damage was generally less than in previous years because spring flights were much later than previous years. Meers says that a wet August tends to favour an increase in populations the following year. 

In Saskatchewan, surveys have indicated the pest’s range has now extended from the Alberta border to east of Highway 4. The northern boundary of distribution appears to be the South Saskatchewan River. It has not been found in Manitoba.

Meers says that Cruiser seed treatment is registered for pea leaf weevil, and that it has given consistent economic returns. Matador is registered as a foliar treatment, but he has not seen an economic return from foliar treatments. Meers also cautions that Decis is not registered, and that using it could result in pea export problems.

Barley mealy bug has also caused localized problems in central Alberta, primarily on barley. Meers says the problem only occurs on cereals grown back-to-back, because the bug does not fly. While chemical control is not registered, a crop rotation with several years out of cereals breaks the insect cycle.

The Hessian fly was also noticed in several areas of Alberta in 2009. Previously most noticeable in southern Alberta, severe Hessian fly damage was noticed on a CPS wheat field near Edmonton. Meers says that the Hessian fly produces crop logging symptoms similar to the wheat stem sawfly. “If the crop breaks off above the node, it is the Hessian fly, because the maggot feeds right above the node,” he explains.

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The usual suspects
Grasshopper has the potential to cause some problems. Grasshoppers may be a threat in parts of the Peace River region and northwestern Alberta. West-central and southwest Saskatchewan have areas of severe risk, as well as areas around Prince Albert. “Grasshoppers look like they may be our biggest insect risk in Saskatchewan at this point,” explains Hartley. “It depends on climatic conditions in the spring, but the fall survey showed some high numbers in those areas.”

Other common insects on the Prairies are running through their typical cycles. The wheat midge forecast map shows localized risk areas in parts of Saskatchewan and Alberta.
Wheat stem sawfly populations were low in 2009, but localized rebounds in the traditional areas may be possible in 2010 with favourable weather conditions.

Flea beetle populations have been gradually increasing, and late infestations in the fall may sometimes indicate a high risk in the spring.

Bertha armyworms are on the low end of their cycle, and no high-risk areas have been identified for 2010. Lygus bug caused some problems in Alberta in 2009, and a dry spring will favour the buildup of lygus bug in 2010. Diamondback moths and some species of aphids blow in on the wind from the US and their infestations are not predictable.

Cutworm risk is also not predictable, but, as in the past few years, cutworms will likely be a problem in those areas that experienced problems in 2009.