Dr. Scott Stewart advises on timely management steps for controlling thrips and tarnished plant bugs in cotton. Play podcast
Ginger Rowsey: Thanks for listening to Call of the Week. Our guest is Dr. Scott Stewart. Scott, what’s your call of the week?
Scott Stewart: The call of the week has been thrips control, and that will continue until next week, but I’m also going to start getting calls about plant bugs. I really want to talk about both. We have cotton anywhere from just starting to square to just coming out of the ground or just just planted, and right now our thrips population is peaking, so a lot of our early cotton is out of the woods from thrips injury. But a number of people have called me talking about the high number of thrips and some of the thrips injury they’re seeing on this later cotton, which is kind of what I’m seeing in my plots, as well. It’s been a surprising jump in the last week or so. I’m just encouraging people to get out there and and scout and make treatments. The seed treatments have been performing pretty well, but we all know they have limitations and really what I want to encourage people to do is probably consider making a foliar application to this smaller cotton at the one- to two-leaf stage. I would especially encourage that if they’re already going across the field with a herbicide application because it’s relatively low-cost when you’re doing that. I think the conditions warrant it even though we’re seeing pretty good growing conditions.
Rowsey: Is there a particular product you recommend?
Stewart: Most people are going to use acephate or Bidrin and primarily that’s economics driven. They perform pretty well, they take a little relief off the plant. My favorite product is a product called Intrepid Edge or Radiant, and it works better but it’s considerably more expensive so there’s a trade-off there.
Rowsey: Also, you said you wanted to talk about plant bugs, looking ahead.
Stewart: And not very far ahead because we’ll start getting calls very quickly, and one of the first things I want to say is on this earliest cotton you really need to be alert for plant bugs because very often what happens is once it starts squaring and it’s the only game in town the plant bugs will funnel into it and you’ll get very high populations in those first fields that start squaring. Once a bunch of other fields start squaring, the populations kind of spread out, but you do have to be alert on that first cotton that comes into square, which is occurring right now.
Rowsey: What’s the best way to scout for plant bugs?
Stewart: Our primary method for scouting for plant bugs prior to bloom is to use a sweep net at 25 sweeps at a time in several locations in the field and you’re targeting adults because you’re dealing with adults primarily in that time window and the sweep net is much better at that. So, encouraging people to do that. Later on our thresholds change a little bit. The first couple of weeks of squaring we’re being a little bit more aggressive and the threshold is 8 tarnished plant bugs per hundred sweeps. So, you have to do the math if you’re doing 200 sweeps, or you only do 75. But then it increases once you get into the third week of squaring to 15 tarnished plant bugs per hundred sweeps. Having said all that, you have to use your judgment a little bit because the other way we really encourage you to monitor plant bug injury is by looking at square retention. We’re trying to maintain a minimum of 80% or higher square retention all the way up to first bloom, and if your square retention gets low, close to 80 or below 80, you need to reduce those thresholds to increase your square set.
Rowsey: What else do producers need to be aware of as far as insect issues in cotton?
Stewart: The primary one is tarnished plant bug this time of year. I’ll go ahead and tell you, if you’re seeing square loss this time of year, it’s probably tarnished plant bug. The fruit just doesn’t fall off the plant for no reason and it’s very often insect injury. So, the next obvious question is what do I do about it? And I would encourage you to follow our thresholds first of all, and make those insecticide applications timely. That’s really critical, by the way, especially at the first two weeks of squaring because you don’t have that many squares in the field, so if you have a lot of plant bugs they can take a lot off the plant percentage-wise in in a hurry. Insecticide selection is a little bit challenging but important.
Rowsey: In what way is it challenging?
Stewart: I don’t think we have a whole lot of choices particularly during that first 2-3 weeks of squaring. I’m still pretty comfortable with the neonics like imidacloprid or Centric. If I’m going to use imidacloprid, I’m going to use it at the full label rate, which does change depending on the product you’re using and the concentration. They seem to do pretty well at maintaining square retention even if they’re not really reducing adult populations that much, and you do have to keep in mind, they’ll migrate back into the field. Once we get closer to squaring I get a little bit nervous about those products because they’re not very good at controlling immatures that might be showing up and that’s when we’re going to start talking about mixing in things like a Diamond or maybe using a product like Transform to control both adults and nymphs with confidence. I’ll blog about a lot of this stuff on our news blog and you can keep up with it, but, like I said, I’m still fairly comfortable using the imidacloprids and the Centrics for the first couple of weeks. My testing last year indicated they’re still providing decent protection of the plant.