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Hi, my name is John Tooker. I am an Extension Entomologyst at Penn State
and we're standing in a soybean field here at the end of July
these soy peas are just about to enter the reproductive stage. They just start to flower
we are going to scout this field see if we can find any insect pests.
One of my goals as an extension entomologist is to try to work with growers to
encourage them to use integrated pest management
and integrated pest management is an approach to assessing insect population in the field
looking for economic damage so we can minimize insecticide use
that is: we want to use insecticides only when it makes economic sense
so we'll walk across this soy bean field today seeing what type of
insects are causing damage
see what type of insect populations are out here to assess whether we have
economic damage
or not. It may be a surprise some people but most
soy bean fields in Pennsylvania do not ever achieve
economic damage. There is insect pest in there that are causing damage
but the populations never gets big enough to actually force a grower to lose
money.
Oftentimes insecticides are applied without necessity
they're just being applied because it makes someone feel better and they're not
actually protecting
economic yield. I just pulled this soy bean plant out of the ground to illustrate one
of the challenges of
estimating the amount of defoliation. Soy beans before the pods are set,
can withstand about 25 to 30 percent defoliation
after the pod is set it is cautioned 15 to 20 percent
defoliation but it's a challenge to estimate how much defoliation
particular plant has.
If you look at that leaf you might estimate that to be about
15 percent damage maybe ten percent damage. It is a
little bit subjective how much damage you cause that is up to you.
We could probably scan that leaf and figure out exactly how much damage
is there but we want to do this in the field kinda of on the fly.
There's a tendency to overestimate the amount of damage about so I might call
that fifteen percent damage is more likely closer to 10. When
we're talking about a whole plant defoliation or not talk about individual
leafs. About how much leaf material has been removed from
an entire plant. This plant seems to have a lot of damage. You can see that
leaf,
that leaf, this leaf has some holes in it but I think on balance the great
majority of leafs have
little to no damage. Treasure assessing the whole plant you have
to take all these into consideration so if I have to ballpark this
I'd call that maybe somewhere between five and ten percent
okay, my five and ten percent might be different than your five ten percent
but what you want to do is get
a good representation of the amount of damage you're seeing and not just rely
on what you're comfortable with
right because were using IPM we're not using
comfort zones we are using actual measurements
loss of yield and remember it is not just an individual plant and lets just if this one plant is fifty
percent defoliated
but the rest of the field looks fine and then you have
a non economic concern. It's kind of the average
damage across the entire field. So the first species we found here is actually a
fairly charismatic species.
This is the Silver Spotted Skipper, it's a caterpillar, the Silver Spotted
skipper butterfly.
It is an occasional pest of soybeans, its kinda pretty little guy with a bright
red head with orange dots on it, striped
yellow body and they're kinda fun
but they rarely cause economic damage what they will do,
is they tend to fold leaves. I am going to put that down, they tend to fold leaves
and then they chew on the leaves causing obvious chewing damage
so this is damage caused by this guy. You can see perhaps in the camera here,
that this was folded over. This is kind of a leaf roll.
They kind of hide inside the leaf role and if you pop that open caterpillar will be
sitting right there.
This individual is pretty large, has to be in one of its last developmental
stages
will probably pupae on its way to becoming an adult soon.
So that's the Velvet bean Caterpillar.
The Velvet Bean Caterpillar causes this type of damage on leaves,
also can feed from the edge but they're easy to
diagnose because they have a very distinctive behavior when you bother
a Velvet Bean Caterpillar. They wigle like crazy. Off course it is not going to do it
on camera. see if... Can you get that?
wiggle. Ahh! did you see it
wiggle men! Opps! Did you see that? Did you get that?
that's awesome
so this is the Velvet Bean Caterpillar again and it causes defoliation but just like
the other caterpillar I mentioned, soybeans can withstand a lot damage from
these guys so
an economic spray wouldn't be necessary until you are at 15 percent defoliation. When you have
pods presence
or closer to 30 percent delation when the pods aren't present.
But they are not that common in most fields but sometimes you'll see
a couple per plant and that's when you really start to notice their damage but
again
because a soy bean plant can withstand so much defoliation
they're rarely an economic concern, occasionally but rarely.
So another pest species that were finding out here in the field today, something
called Soybean Aphid
Soybean Aphids are awfully small little yellow dots on the underside of leaves.
they tend to prefer to colonize the really young leaves so the foliage at
the top of the plant. Then they
slowly spread across the plant. Soybean aphids can be awfully damaging if
they get the really big populations
in fields like these though where we haven't used insecticides, lady beetles and
other predatory insects do a great job
holding back Soybean Aphids. populations
For a while in Pennsylvania, we had a two-year cycle where we had low
aphid populations and big aphid populations, the last year we had a
really big aphid numbers in Pennsylvania was 2009.
Since then the population has been awfully low and they haven't been an economic
concern
so they're certainly here and growers are nervous that they're in their fields
but as long as you use IPM and scout and look for the pest
you can determine whether a problem for you or not.
So everyone's familiar with stink bugs these days because the brown marmorated
stink bug.
this happens to be a good stink bug and a good stink bug is one that's a
predator
so this is something called the spine soldier bug and it's a beneficial insect.
it prowls around crop fields like this soybean field
and eats soft body insects, so you can see this one here has
a caterpillar on the end of its beak. At the end of its mouthpart
and this caterpillar is pretty much done causing any damage
to this
soybean field so one way on that
integrated pest management is beneficials as we avoid insecticidal sprays unless
absolutely necessary
because we're trying to maintain population to these good insects that
can kill
the pests that are trying feed up on the field so this
caterpillar likely caused some damage that looks like that but
because that stink bug has killed that, sorry caterpillar,
the damage has stopped so the grower doesn't have to worry about that particular caterpillar
anymore, right and soybeans are a great place for that to happen because
how close the canopy is there's a lot of good kinds of
micro-environments down there for natural enemies to live
and a they'll help protect your fields.
So here we have Japanese Beetle, we have four individuals feeding and this
kind of lacy damage is very distinctive of Japanese Beetle.
Japanese beetles tentd to aggregate like this because while they're feeding
an odor is emitted from the plant and that oldor attracts other individuals, they
kind of
group together like this. They can mate
if they all get together.
They can also kind of feed altogether and if you can see
others places in these field we have very distinctive
and the lacy damage attributable to Japanese Beetle
but again because soybean is so good at tolerating damage,
this is a low-level damage and is not an economic concern
that's called a Syrphid Fly or Hover Fly
and adults are very common
floral visitors but the larvae of that thing are aphid feeders
so I showed you a Soybean Aphid earlier, the maggot of this fly
will wander around soybean plants looking for
soft-bodied insects to feed upon and they'll often find aphids and that'll be a wonderful
treat for them but we got a couple flying around here.
The next species that we run across here in our soybean field.
This is the Bean Leaf Beetle, this is the adult of the bean leaf beetle
and it causes this type of damage causing little holes
in the leaves it's not quite the same as Japanese Beetle damage which is more
lacy type damage but these little holes they can add up.
One challenging thing about Bean Leaf Beetles is they can come in a variety of
colors
so this is a yellow one with black dots there also red ones with black dots
but the key is this all triangle kinda right after their neck
so that neck is what I'd call therefore act right behind their thorax.
Right behind their thorax, is a little v triangle, black triangle
that is always there whether it's a red one or yellow one like this
but it's all been leaf beetle and rarely do they cause economic damage
this time of year so again we're at the end of July.
They can cause more of an economic concern in the spring
when soybeans are just emerging from the ground and they're attacking the cotyledon
stage of soybeans
also, they have two generations a year but this time of year
it's not a huge concern. One exception to that would be if they're feeding on the
pods
this field here, the soybean pods have yet to form
but if you have large populations of Bean Leaf Beetles feeding on pods
and there is a lot of pod damage, then you have an economic problem that would require
treatment
but prior to the pod formation where they are just causing this kind of cosmetic leaf
damage it's no great concern. So one of the more common insect species that we would be
able to find here in these soybean field today
are grasshoppers. We have adult grasshoppers, we have nymph grasshoppers
and they appear to be fairly common
grasshoppers like these though, are rarely economically damaging
in Pennsylvania soybeans, they are more problematic in the Great Plains
or even on the Eastern Shore of Maryland and Virginia
where for some reason grasshopper populations you just go wild
but here in Central Pennsylvania they are not that big of a deal.
You see them hopping around a lot. You see them causing a little bit of damage but again they
never really
cause that 30 percent defoliation that would be relevant
for economic control in soybeans so we've spent a fair amount of time in this
soybean field today looking for insect pests
and not surprisingly to me we haven't found that many. Again most soybean fields
beset by insect problems just occasional fields are pretty well
infested
so the key to controlling insect pest effectively in this type a field is to
getting out there
and scouting to see what's out. Seeing what's causing the damage
is key to understanding what needs to be controlled. So today we found Bean Leaf
beetle,
we found Silver Spotted Skippers, we found Japanese Beetles,
we found a couple of caterpillar species besides the Silver Spotted Caterpillar
and they're all causing relatively low amounts of damage.
The main pest I would be concerned about would be Soybean Aphid.
Soybean Aphid populations can grow awfully fast
but if you have a good population natural enemies that's going to
substantially spoil their growth even stop their growth
so I would recommend not doing anything with this field. That is not applying
insecticides,
coming back in two weeks scouting it again
seeing what the past population looks like. It's likely that this field would
get through all the way to harvest
without needing an insecticide application and again
that seems to be the case for the great majority of soybean fields
in Pennsylvania. They're out there going effectively
and not being dogged that much by insect pest populations.
All right well also thank you for joining us today as I scouted this soybean field.
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