Importance and Control of Kudzu Bug in Soybeans - March 2014Link to transcript
"Importance and Control of Kudzu Bug in Soybeans"
[Jeremy Green – Professor of Entomology, Clemson University. Picture of Jeremy in a field. Pictures of Kudzu bugs. Arkansas Soybean Promotion Board. U of A Division of Agriculture Research and Extension University of Arkansas System.]
Alright, so we’re going to talk about kudzu bugs. I mentioned we’ve been experiencing this insect for several years now in the southeast. I’m going to take you through just about the entire history of it being here and what we’ve found out about it. [Slide - Picture of a someone holding a crystal ball – Prediction: Kudzu bugs will continue to establish in the Mid-South and become an important nuisance and agricultural pest. Slide – Picture of publication: Kudzu Bug Identification in Soybeans. www.kudzubug.org. www.clemson.edu/extension/kudzubugs/. Up-to-date map of distributions. Links to Extension materials. United Soybean Board publication.]
Just a little bit about the species and what it looks like. [Slide – Pictures of Kudzu bugs in various stages.] You’ve got egg masses laid in two rows, the immatures hatch from those and develop through five instars, much like stink bugs before they become adults. Give you an idea about the size of the adults, they are about the size of an eraser on a pencil. About the same size as a lady beetle. It’s unlike anything you will see in soybeans. [Slide – Picture of Kudzu bugs on leaves with a dime to compare size.] You will see this insect in large numbers on non-legume hosts. It will rest on anything in large numbers and almost look like it’s feeding and hurting that host plant. But its preferred hosts are legumes. [Slide – Various pictures of Kudzu bugs in various stages on legume and non-legume hosts.] Soybeans, kudzu is a legume, wisteria is a legume, peanuts is a legume, but interestingly, this insect doesn’t like peanuts. You can find them on peanuts, but it doesn’t use it as a reproductive host.
Kudzu is its preferred wild host. [Slide – Pictures showing overgrowth of Kudzu. Kudzu bug is a beneficial bio-control agent of Kudzu, capable of 30% + reduction in biomass. Zhang et al. 2012 – Environ. 41 (1): 40-50.] The “kudzu bug”, incidentally, is not its approved common name, it’s just what we call it because if you go in a kudzu patch, it’s in the kudzu patch in an infested area. You are going to find it on kudzu first. It’s actually the good guy on kudzu. There’s a published paper already that it reduces kudzu growth by 30%, so it’s actually a bio-control agent of kudzu. It’s not going to eradicate kudzu, not going to get rid of kudzu, it just feeds on it and slows its growth down.
Kudzu occurs in a very large portion of the United States. Pretty much where we grow soybeans. The whole eastern half of the country, so those two hosts overlap nicely for this insect. [Slide – Map of the United States showing the distribution of kudzu in the United States. Slide – Map showing the portion of the United States that produces soybeans.]
This is a video one of my graduate students took about a dozen sweeps in an infested area of this field. It’s pretty dramatic. You see these things just boiling out of the sweep net. [Video showing a sweepnet full of kudzu bugs.]
You can find it early. This is an early May picture. Early vegetative soybeans like B2 and they are just covering every stalk in the field. Pretty abundant quick. And at the end of the season, they can be really thick if you don’t do anything about it. [Slide – Picture of soybean plants with kudzu bugs covering the stalks.]
This is where kudzu bug is from. It’s from Asia. That’s where we get a lot of our invasive species, but they’ve been here since 2009. [Slide – World map with Asia circled showing the native land for kudzu bugs.]
They are found on some homes next to a kudzu patch [Slide – Pictures taken in late October 2009 in northeast Georgia showing kudzu bugs on a home.] This insect likes the color white, so it’s going to be on your truck if it’s white, the house if the trim work is white.
It was limited to these nine counties in northeast Georgia in 2009. We checked around and this was the limit of its distribution in late 2009. [Slide – Map of Georgia showing the nine counties in 2009 with kudzu bugs.]
This is a picture of where we got the end of last year, 2013. It’s in multiple states in South Carolina, North Carolina, most of Georgia, all of Alabama, it’s in Mississippi and it’s over to the river and it’s just a matter of time before you got it here in Arkansas. [Slide – Map showing the distribution of confirmed kudzu bugs in the southern part of the United States from 2009-2013.]
Some of the limitations that you can imagine for distribution of this insect probably the mountain ranges here, but it’s going to be just a matter of time before this thing funnels up and gets into some big soybean acres and then it will be limited probably by temperature. [Slide – Topographical map of the United States.]
This is kudzu, the terminal growth of kudzu and this is what happens when kudzu starts to green up, they start laying egg masses around on the terminals and start colonizing this favorite host plant and then you’ve already seen this picture, they can move straight in to soybeans. [Slide – Picture of oviposition in kudzu: mid-April and May. Slide – Picture of soybean plant stalks covered in kudzu bugs.] If you’ve got early planted soybeans, this insect doesn’t have to have kudzu to survive. As long as there are early-planted soybeans, it will come straight out of wintering sites as adults and move right into early-planted soybeans. So I think you’ve got kind of a perfect storm set up for this insect out here in the Mid-South.
Then it migrates in large numbers to soybeans about mid-summer and can get very abundant early on. The eggs are laid primarily under leaves and you can find a lot of egg masses out there. It’s very distinct, two rows. The nymphs have this kind of fuzzy appearance. [Slide – Picture showing kudzu bugs on soybean plants. Adults migrate to soybean during June and July. Slide – Picture of a soybean plant in July 2010 covered in kudzu bugs. Slide – Pictures of eggs on the underside of a soybean leaf. Slide – Picture of nymphs on stalks.]
Alright, so how does this insect feed? It’s not a leaf chewer, it doesn’t feed on the pods. This thing is a stem feeder, much like the three-corner alfalfa hopper. [Slide – Kudzu bug – Kudzu bug adults and nymphs feed on the main stem and leaf petioles with sucking mouth parts; Feeds on plant sap and secret honeydew; Feeding causes purplish lesions on stems; Does not feed on pods!; Stress inducing pest – can reduce: pods/plants, seeds/pod, seed size. Drawing of a kudzu bug.]
It feeds on the stems, the petioles, and it’s a stress-inducing pest. It’s another factor out there that stresses the plant. It takes a while for the populations to get going to put enough stress on the plant to hurt yield. [Slide – Picture of kudzu bugs on plant stalks.]
Alright, so we’ve done a lot of work on treatment thresholds and some of this maturity group plant data work and I don’t have a lot of that work summarized yet. We’ve got to do more analysis on that to kind of nail down threshold, but we’ve looked at things like an untreated control, full protection, one bug per sweep, two bugs per sweep, one bug per sweep with nymphs present and then a single application at beginning pod fill, pod formation. What we found out is the key is to control the nymphs. Control the reproducing populations. If you can get in front of a population that’s trying to develop in the field, you can do a pretty good job. [Slide – Treatment thresholds – Initiate treatment of kudzu bug density levels, sample bi-weekly using sweep nets. Insecticide applications: Endigo ZC (lamda-cyhalothrin + thiamethoxam) at 328.6 ml/ha (4.5 oz/acre); Randomized complete block design with 4 replicates; Treatments: untreated control, full protection (spray bi-weekly from bloom to beginning senescence), 1 bug/sweep, 2 bugs/sweep, 1 bug/sweep with nymphs present, single application at beginning pod formation (R3/R4).]
We’re going to have a number to put with that recommendation in here pretty soon, but this publication, we pretty much read that you’ve got to time that application for nymphs. One nymph per sweep using a sweep net or I personally like an observation threshold where you go in the field and you just push back the canopy and look. If you can easily see the hatching nymphs on most of your observations it’s time to spray. Once you kind of hit those things hard, you can evaluate later and once nymphs come back, second generation, you hit them again.
So the pyrethyroid provide new control, there is going to be some reinfestation, particularly if you spray too early and we show some evidence that we probably don’t need to spray too early. Don’t let kudzu bugs complete a generation on soybeans. Immature is definitely important. I really like this observation threshold. [Slide – Kudzu Bug in Soybeans – When to Treat? What to use? What else to consider? Most pyrethroids provide good control, but re-infestation by adults should be expected, particularly early. Do not allow kudzu bug to complete a generation on soybeans! Immatures are definitely important! One generation definitely will occur on soybeans, perhaps two are possible. Time applications for nymphs: one nymph per sweep using a sweep net, When nymphs are easily observed on stems at random locations in field when spot checking.]
So more information can be found at kudzubug.org or our Clemson website. I think that’s pretty much it. [Slide – More information – www.kudzubug.org, United Soybean Board publication: Kudzu bug identification and control in soybeans. Up-to-date map of distribution. Link to Extension materials; www.clemson/extension/kudzubugs/.]