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Western bean cutworm: what to expect in 2012

The western bean cutworm (WBC) is expanding its range across Ontario and Quebec, as well as becoming a pest in some areas for corn producers. Since the first western bean cutworm moths were captured in a cornfield in Lambton County and a bean field near Blyth in 2008, the insect has pushed further east and north.

Cara McCreary, acting field crops entomologist for the Ontario Ministry of Agriculture, Food and Rural Affairs (OMAFRA), says the WBC has now been reported as far north as Temiskaming, Ontario, and as far east as Kamouraska, Quebec. In addition to appearing in new areas, the number of average moth captures in Ontario has nearly tripled from those in 2010.

In some cases, the numbers were high enough to call for control measures. “There were some isolated areas in Chatham-Kent, Lambton, Elgin, Middlesex and Norfolk where threshold was reached and we needed control,” says McCreary. The threshold for WBC is considered to be the point at which five percent of the scouted corn plants have egg masses on them. According to the recommendations, 20 plants should be scouted in five different areas of the field. “If five of the 100 hundred plants have eggs, that’s considered threshold,” says McCreary.

Tim Wellbanks, lead agronomist for Maizex Seeds, based in Tilbury, Ontario, says WBC is moving relatively slowly and is becoming an issue in hot spots that have emerged, particularly in areas from Bothwell to Strathroy and near Tillsonburg. “We learned that where you’ve got it, it can feed significantly and cause quite a bit of damage, leaving the kernels more susceptible to various ear moulds,” says Wellbanks.

Noting that crop specialists are striving to learn about the behaviour of the WBC, Wellbanks says he suspects the insects seem to favour the sandier soils, an attribute which may help explain the locations of the hot spots. Echoing that, McCreary says that higher populations of the pest are overwintering effectively in the sandier soils. “They overwinter in the ground as pre-pupae and they seem to do that more successfully in sandier regions,” she says. “It may have something to do with soil structure, possibly making it easier for them to emerge from a sandier soil.”

McCreary estimates the average yield losses at about seven bushels per acre – or a 3.4 percent yield loss – in areas where eggs and larvae were present and feeding damage was observed.

Scott Fife, Pioneer Hi-Bred agronomist for eastern Ontario, has participated in the WBC trapping network for 2010 and 2011. He says several moths were captured in 2010 and minimal feeding damage was observed in a farmer’s test plot near Perth, Ontario. He also notes that OMAFRA reported feeding damage in the Chesterville area in 2010.

As for 2011, Fife is not aware of reports about feeding damage, but moth captures were higher, doubling the amount from 2010 in some areas. “In some cases in Prince Edward County, there were around 100 captures in a week,” says Fife. “Definitely the moth catches have gone way up. But I think the levels are still low enough that it’s pretty hard to find (WBC) feeding.”

The WBC’s expansion into Ontario and Quebec follows a trend that has developed for the past 10 years.

Known more as a pest for several decades in western Corn Belt states such as Colorado and Nebraska, the WBC started chewing its way through Iowa, Illinois and Michigan before landing in southwestern Ontario.

Not only does McCreary expect to see migration continue in 2012, but she also says that the potential exists for the moth numbers to climb in the susceptible locations.

“I think, especially in areas where there’s sandy soil or silty loam soil, if they’ve experienced heavy infestations this past year, then there are likely to be overwintering populations.”

Fife concurs, adding that it will be just a matter of time before the WBC gains a stronger foothold in the eastern part of the province. “We basically had the same number of traps in 2011 as 2010 in my area, and we saw big increases in the numbers. So there is reason to expect that will continue next year,” says Fife. “Again, it is far down the list of priorities at the moment for growers in my area, but that will certainly change in the next couple of years and they’ll have to start thinking about it.”

When it comes to combating the pest, growers have some options.

Jocelyn Smith, a research associate at the University of Guelph, Ridgetown Campus, is part of a team that is studying genetic traits and insecticides under Ontario conditions. Herculex I, utilizing the Cry1F gene, on its own or as part of the SmartStax configuration, has shown good control of WBC. “We agree with data from the U.S. that shows that with SmartStax and the Herculex, I basically have the same control at about 70 to 90 percent,” says Smith.

The group also tested the Agrisure Viptera trait, which approached 100 percent control. At the other end of the scale, the original MON 810 YieldGard gene (for corn borer only) offered no control of WBC. Although the test results are still being analyzed, Smith says insecticides such as Matador and Coragen showed good control.

While conducting the research, Smith says they also found that an increase in ear mould was more harmful to the plants that had heavy WBC feeding. Therefore, she says, they are currently analyzing all of their trial samples for mycotoxin.

On a more positive note, the researchers are encouraged by the impact of natural populations of predators and parasites on WBC in Ontario. “There were some natural enemies that were found either feeding on or parasitizing the western bean cutworm eggs,” says Cara McCreary. “We saw some of that in Bothwell, where some of the heaviest infestations were.”

As the western bean cutworm continues to make its way into more and more areas, scouting for the pest will be crucial. “Keep an open mind to the possibility of infestation because there can always be hot spots in small areas that you wouldn’t necessarily expect,” says Fife, noting that Prince Edward County is a relatively small corn-growing area that trapped a relatively large number of moths. “Even though numbers in eastern Ontario are still low, you might be in a hot spot.”

The WBC lays its eggs on the upper side of the leaf of corn plants, usually close to the top of the plant. “You have to walk through the field and look up,” explains McCreary. “They’re difficult to see. When the sun is out, you can see the shadows of the egg masses through the leaf. That’s helpful because they are hard to find.”

She suggests people choose five areas of the field and scout 20 plants in each section, looking for egg masses in the top part of the corn plant. For dry beans, McCreary says people should check for feeding damage. The larvae will start feeding on the leaves and move on to the pods when they get larger.

“In a dry bean field there is no established threshold, so it’s basically…if you find WBC feeding damage, spray.”

If the threshold is met in corn, McCreary says the next thing people should pay attention to should be the eggs’ colour. The freshly laid eggs will be a pearly white. McCreary says the eggs will turn to a deep purple when they’re about one or two days away from hatching.

“When they turn purple, wait one or two more days and then you spray because as soon as they hatch the really small larvae are the ones most susceptible . . . and that’s where you’ll get the most control,” she says.

As the researchers prepare for another year of scouting and tracking the progress of the WBC, they encourage people to learn more about the pest and to keep tabs on the moth catches during the season.

McCreary says that concerned farmers can receive information by sending an e-mail to"> or by visiting the Canadian Corn Pest Coalition website at

March 1, 2012  By Blair Andrews


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