Hi, I'm Brian Jensen with UW-Madison Department of Entomology and Division of
Extension. I would like to talk to you today a little bit about black cutworm
management in seedling corn, why cut worms are an occasional pest on corn.
Because they don't overwinter up here but migrate up to our state on spring
weather fronts, we never know for sure if that migration will be to our west to
our East, or gets stalled out to our south, or if we'll get a lot of moths flying up
here. The immature stage is what is what
causes the damage to our corn usually from emergence up to v4 stage of
development. After that the corn pretty much out grows out of black cutworm damage.
Here's an example of larger cut worms feeding on mid-sized corn v3 v4. They are
burrowing into the plant below ground level and they're feeding right at the
growing point. And above ground symptoms that you'll see are this wilted whorl
eye, and sometimes a the plant may be laying over. So dig around within 2
inches of a damaged plant looking for the black cutworm, and you won't find
them around every plant, but here we did find one. The immature stage at best is
described as kind of a grayish color light gray dark, gray maybe sometimes black. But I look at
both finding the worms and the type of damage that they caused before I say
it's black cutworm damage in a field. I always advocate scouting each and every
field that you've got. I also understand in the spring you don't always have the
time for that, so what I'd like to give you is a couple hints to target fields
which have the highest probability of seeing black cutworm damage. And those
areas are corn planted after soybean stubble for some reason- the adult female
moth likes to key in on that soybean stubble to lay eggs.
Also you can find significant black cutworm feeding in fields that have low
densely growing broadleaf weeds in them. And then finally those fields
with low lying areas next to streams wet spots and things like that. To scout for
black cutworm I would suggest you walk a w-shaped pattern within a field. That
gives us a good random assessment of the entire field. And at each of five areas I
would count the type the damage that you have on 50 consecutive plants. So a field
sample is 250 plants. The type of damage that cutworms caused is dependent on the
size of the cutworm, and it's also dependent on crop stage. Small larve can
only cause holes in leaves. They can only make holes in the leaf. They cannot cause
any cutting. Medium stage black cut worms can, on small corn, cut the plant. And
large larvae are pretty much going to burrow into that plant below ground
level, and your above-ground symptoms will be what we commonly call dead heart
or wilted whorl. So in probably two damaged plants and each set of 50 plants
I would dig up next to a damaged plant dig up and try to find the worm. It's
important to know how large that cut worm is; and the length of the cut worm
is not very diagnostic. Rather I would use the head capsule gage that's in our
pest management in Wisconsin field crops bulletin and finally the economic
threshold for black cutworm x' we're only looking at the growth stage of e1
through about 3/4 on corn and if you have approximately 5% damaged plants on
field average then it could be time to this brave there are really no cultural
management characteristics that or cultural
management practices that you can use for more information please go to our
our extension bullets in a 3646 pest management and Wisconsin field crops
thank you