Core Topic Briefs: Soybean Field Pest Walk with John Tooker
Esta exploración se realizo en campos de soya de Pensilvania. El objetivo de esta actividad de exploración era buscar plagas de insectos para determinar a través del Manejo Integrado de Plagas si la aplicación de un insecticida es necesaria. Durante el proceso, muchas especies de insectos, incluyendo los organismos benéficos, se determino si los umbrales económicos se han alcanzado.
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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