WBC – What We Learned in 2010

I am sure we will be talking about western bean cutworm all winter but there are a few key learnings that we gained in 2010 that I thought I would point out:

1.  The dark bands behind their heads that we use to identify the larvae are not obvious until their last few stages of instars.

2.  Fields with sandy soils had the heavier infestations, at least in corn.  Bothwell to Newbury had the heaviest, though sandy fields in other counties also had their share of damage.

3.  WBC moths are like Goldilocks.  They want their corn field to be in just the right stage to lay most of their eggs in.  If the crop is too young (ie. in the whorl stage) the larvae will die.  If the crop is in full tassel and shedding pollen, they are not interested.  The crop needs to be in pre-tassel to be JUST RIGHT for them.

4.  On average. the damage in both corn and beans was not as bad as it could have been.  Most fields have low levels of feeding.  This is probably due to most of the corn crop being past the crop stage they prefer to lay their eggs in.  Now as for beans…I am not sure why we have not seen more damage.  I think some of the later planted beans that are just being harvested might find more feeding once the combine goes through.  But the bulk of the moths had to lay their eggs somewhere after peak flight took place the week of July 25th.

5. I think we are fortunate that harvest is happening early so that the crop is off before ear rots and pod diseases could set in.  During our surveys, the corn kernels were maturing so quickly that the larvae had to dig down closer to the cob to beat the milk line.

So what does this mean for 2011?  There are a lot of larvae that are going to try to overwinter.  The sandier the soil, the more successful they will be.  So fields that already had moderate to heavy pressure this year should expect the same for next year.  Plant early to try to get the corn crop beyond pre-tassel by peak flight so that the moths avoid laying eggs in your field.  Bt corn containing the Viptera trait will provide control.  Products containing Cry 1F (Herculex or SmartStax) will provide protection but some feeding may still occur.  Not every field will have infestations next year but we should expect that 2010 was just a hint of what may come in 2011.

2 thoughts on “WBC – What We Learned in 2010

  1. I Tracy,

    I found 2 cobs with damage along pheromone trap in Shawville, QC, with western bean cutworm mature larvae. Many other cobs had corn borer damage (easy to recognize). It is too late now to do a proper scouting since damage could be any beast: corn borer, corn earworm, fall armyworm, or western bean cutworm.

    1. Hi Francois

      WBC feeding is very different from ECB. ECB does not gorge on the ear like WBC does. The others are a little more difficult to sort from each other. To be 100% sure you really do need to see the actual larvae which is starting to get to be too late to find now. But there are a couple of signs you can go by. Both WBC and FAW can leave entry/exit holes on the husk but WBC doesn’t always enter from the side of the ear. I often find that WBC feeds throughout the ear and this year, because the kernels were drying down so quickly, WBC had no choice but to drill down towards the shank so that it could feed on the moist parts of the kernel below the milk line. But when the feeding is only at the tip of the ear, you really can not be 100% sure it is WBC versus the FAW or CEW. Just make note of those fields this year and try to scout fields nearby earlier next year to confirm. As WBC becomes more common up your way in Eastern Ontario and Southern Quebec, it will probably be easier to tell.

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