Western Bean Cutworm Moth Captured in Ontario

Just a week after putting up our pheromone traps in Ontario, we have captured the first western bean cutworm moth. This is the first record of WBC in Ontario, though as mentioned in last week's article, it was an expected event for us in the near future. I was just hoping that it wouldn't happen so soon.

Catching a moth does not mean we will reach threshold levels this year. It does indicate that WBC can make it here and therefore we now have the potential to experience injury and need to monitor traps regularly to observe when peak flights occur and scout our corn and bean crop to monitor for activity.

Peak flight in neighbouring jurisdictions tends to occur in mid to late July. With no reports of damage or trap captures in Ontario in 2007 we are assuming that the moths are just arriving from the US so we will also monitor activity in Michigan and Ohio to help predict activity. Only one site so far (Port Lambton) out of our 18 trap locations captured an adult. We will be checking all of our traps each week and will let you know if more moths are captured.

Other jurisdictions recommend scouting in corn to start weekly, one week after first trap capture particularly in areas where moths are captured. Though beans are also at risk, WBC do prefer to lay their eggs in corn, especially before it tassels. Other states indicate that only if they accumulate 700 or more moths in their traps before the peak flight are beans also at risk and would then require treatment in 10-20 days after peak flight. Bean fields neighbouring corn fields that required treatment most likely also require treatment. But given that we have only captured one adult so far, let's focus our scouting efforts on the corn crop first.

In corn, particularly fields in Lambton county where our first moth has been trapped, scout 20 plants in 5 areas of the field. Focus efforts on the top three to four upper leaves of the plant where the majority of eggs are laid. In corn, WBC lay their eggs on the upper surface of the leaf, preferring hybrids that hold their leaves upright. So admittedly, scouting in corn is not going to be fun, especially if you are vertically challenged. I might need to buy a step ladder!

WBC eggs are pearly white when first laid and are shaped like tiny cantaloupe. As the eggs mature, they turn tan and then purple in colour. Eggs hatch in about 5-7 days. University of Nebraska recommends treatment in corn when 8% of the plants scouted have egg masses or small larvae. If the eggs have hatched, spray at 95 percent tassel emergence or if tassels already emerged, when most of eggs are expected to hatch.

Figure 1. Newly laid Western Bean Cutworm eggs.
(Photo Credit: Marlin Rice, Iowa State University)

Figure 2. Western Bean Cutworm eggs turn purple as they mature
(Photo Credit: Marlin Rice, Iowa State University)

If there is an indication that we are going to experience threshold levels this year, an emergency use registration for foliar insecticides will be submitted. But for now, my recommendation is to not panic but to start to scout in particular, those areas that we capture moths in.

Next week I will discuss scouting procedures for the bean crop and keep you informed about our trap captures.