Crop Scene Investigation - 30: What's clipping Wilson's wheat?
Wednesday, February 2, 2011
by BERNARD TOBIN
Tracey Baute, an entomologist at the Ontario Ministry of Agriculture, Food and Rural Affairs, knows her insects. But it's hard to put your finger on a problem pest if you can't find it.
That happened this summer when Baute got a call from Wilson, who farms near Rodney in Elgin County. He wanted her to identify the culprit that was clipping the heads off plants in his winter wheat field.
Before setting foot in the field, Baute had pegged the likely pest. All she had to do was get a visual identification to confirm her suspicions.
Right away, I was thinking armyworm, explains Baute. who immediately sent student scouts out looking for the pest. There was no real leaf feeding on the plant, quite literally just heads in square metres clipped off and laying on the ground.
Using flashlights, she and her troops searched the fields in the evening and early morning – typical feeding time for armyworm – looking for larvae activity. Sometimes, you can find armyworm up on the plant feeding and we were trying to catch them in action, she says. But too few of the pests were found to consider the case closed.
Just as Baute and her team were coming up empty in Wilson's field, more reports were coming in from farmers who were having the same problem.
Growers were calling saying they're finding clipped heads. Sometimes even sections of the stem were clipped off and lying on the ground as well, recalls Baute. There were times when it would literally take down an entire plant. But in all these cases there was no evidence of frass, the tiny dark pellets an armyworm passes as waste after digesting plant parts.
While the damage was not widespread in the fields, small areas were experiencing tremendous injury. The pest appeared to be much more aggressive than armyworm, which has a threshold of four larvae per square foot.
With armyworm declared innocent, Baute then turned her thoughts to corn earworm. All the reports coming in from the damaged fields noted sightings of green caterpillars.
There is no caterpillar in wheat that is green, she thought, but there might be an explanation. With the extremely summer-like spring conditions, corn earworm may have transitioned to wheat in search of food. Beyond armyworm, that would be the only way to explain the presence of green moth caterpillars.
Baute was getting desperate to find an answer. She needed to identify the pest quickly if she was to prescribe an insecticide treatment that could be sprayed before the wheat pre-harvest application window closed. She sent out emails to her entomologist colleagues across the continent to see if they could help and headed back to the fields to do more scouting.
This time she arrived at the field in the middle of the day with a sweep net in hand. I thought if we're not finding them at night, let's try on a cloudy day. When we looked in the sweep nets, we saw these larvae. And given the numbers that we were finding, they had to be the culprit.
What Baute found was a bright, grassy-green larva with many legs and a bright orange head that was tucked under its body, giving it the appearance of looking downward as it tried to feed.
Baute immediately recognized the insect, but she couldn't understand what it was doing in a wheat field. She quickly sent the pest off to Ottawa to confirm her identification. And then an email from a colleague helped solve the puzzle.
Do you know what pest was clipping Wilson's wheat? Send your solution along with your contact information to Better Farming at: rirwin@betterfarming.com or by fax to: 613-678-5993.
Correct answers will be pooled and one winner will be drawn for a chance to win a Wireless Weather Station. The correct answer, along with the reasoning followed to reach it, will appear in the next issue of Better Farming. BF