Soybean Field Scouting

Soybean Field Scouting


Hi, I’m Gus Lorenz Extension Etomologist with
the University of Arkansas. What you see behind me is a soybean field. And, it’s mid-September,
it’s that time of year. We have a late crop this year of soybeans and what goes along
with a late crop is obviously insects. And, we have a lot of pressure in this field today. We’re outside Marianna at the Lon Mann Cotton
Branch Experiment Station in some of my plots. I want to show you some of the damage and
some of what we’re seeing out here right now. So what we got going on in this field, there
is several things. You can see the immature brown stink bug nymph, and it’s distinctive
from the brown stink bug nymph beside it. And here is the adult brown stink bug between
my thumb and forefinger, just to show you the different stages we have out here right
now. And here is what causing the defoliation that
we’ve been looking at out here. That’s called the bean leaf beetle. It’s characterized by
it may or may not have those spots on the back, but they all have the little triangle
behind the neck. Here is a red one with no spots on it., but again it has the black triangle
on it right behind the neck. So they come in several different colors. We not only have bean leaf beetles and stink
bugs, we also have soybean loopers coming in the field. The Soybean looper is characterized
by the two pairs of prolegs. The soybean looper is the only species that have two pair of
prolegs. Bean leaf beetles will often times cause extension
defoliation in the upper part of the plant, but what you need to look at is not only the
to top part of the plant, but you need to look down through the canopy and look at the
level of defoliation across here. When I look at this leaf here in particular. Our threshold
is 25 to 30% defoliation, and what I see here, we have exceeded that threshold. But, on this
leaf right here we are only at about 10%. So when you are looking at defoliation and
trying to make a decision on whether or not you’ve reached that threshold of 25% defoliation
you need to look at the entire plant and not just that part up in the top. The thing about lopers is they are just the
opposite of bean leaf beetles. They like to start down in the lower part of the canopy
on the older tougher leaves and then they work their way up into the new growth. So,
you have loopers working their way up from the bottom, and bean leaf beetles coming in
from the top. The thing is, if we come in and treat these
stink bugs with a parathyroid to get them under control, what it acturally does is destroy
the beneficial complex, kills all the parasites and predators, and opens the door for the
loopers to blow-up. So, what you have seen out here today is a
combination of pests. And in that situation at this time of year it’s going to take more
than one insecticide to clean up this mess out here. In the case of the stink bugs and
the bean leaf beetle a product of choice for those two would be Bifenthrin, which a trade
name would be Brigade, Fanfare, Discipline, Sniper, there is several different brands.
At a rate of a gallon per 25 to 30, or something like that, just to get those under control.
As I mentioned earlier, if you spray a parathyroid out here the chances of you blowing that looper
complex up, the loopers that are out here is pretty great, because you are also wiping
out your beneficial complex. So in that case, you have a few options for products on loopers
that you would tank-mix with that Bifenthrin. Prevathon, Besige, Belt. Another that might
be a little cheaper alternative would be Intrepid. So, those are the products that have proven
to be very effective for loopers. So you’ve got to tank-mix with one of those. And for
that situation it’s a pretty expensive treatment when we get into trying to control more than
one pest species. And there is not just one product that gives good control.