I'm Ryan Miller, Crops Extension Educator. Earlier this morning, we recorded an episode of the Strategic Farming Field Notes program. Strategic Farming Field Notes is a weekly program addressing current crop production topics. A live webinar is hosted at 08:00 A.M. on Wednesdays throughout the cropping season. During the live webinar, participants can join in the discussion and get questions answered. An audio recording of the live program is released following the webinar via podcast platforms.
Thanks and remember to tune in weekly for discussion on current cropping and crop management topics. All right. Good morning and welcome everybody. I'd like to welcome you today to our Strategic Farming Field Notes session. These sessions are brought to you by University of Minnesota Extension and also support from the Minnesota Soybean Research and Promotion Council and the Minnesota Corn Research and Promotion Council.
We'd like to welcome you today to our session on corn worm getting your corn down. I'm list I'm a regional extension educator and crops out of the Worthington Regional Extension Office. I'll be moderating today. We welcome Bruce Potter. He's our IPM Specialist out of the Southwest Research and Outreach Center by Lambert, and also Dr. Fay, he's our new extension corn entomologist. We're happy to have him on board as well too, and learn more about what he's doing and seeing as well.
Anyway, with that, we'll just jump right in. We did get some questions earlier on with the registration that do relate to our topic today. Again, we're going to focus on corn worm, but we'll hit other pests if we have some time. But basically just take a step back before we dive really into the details.
Could you just explain, maybe we'll start with Bruce here just talking about what's the corn worms life cycle through the stages, what are things that we got to worry about, When can we actually control these pests and so forth. But again, just give us a little basics so we're all on the same page here. Well, sure to start with, at this time of year, basically, for the most part all your rootworm management is get directed towards the following corn crops.
Right now the beetles are mating, are laying eggs. Rather those eggs will diapause, they have to rest over the winter. They'll hatch in the spring. The larvae hatch usually the beginning of June, 1 week of June or so in this part of the world. They'll feed for a few weeks, they'll pupate and then the beetles will start coming out in, in mid to late July. Beetle emergence is still happening, so it's not like all the Beatles eggs hatch at the same time and beetles emerge at the same time.
It's a long extended period that ties into scouting. And the other thing that varies between, we've got two species we're dealing with in Minnesota, Northern corn rootworm and Western Cort worm. The difference between the two species is that northern corn rootworm have evolved a way to get around a crop rotation. And they simply do that by delaying part of that population, delaying egg hatch or another winter, sometimes 34 winners.
And that'll put them back into either you get around environmental stress that way or you can get around pretty short corn soy bean rotation with that egg catch strategy. Okay, good. Yeah, thanks for that. And then of course, people wonder what are key ways to control corn rote worm. And I don't know if you want to take that, maybe just think about what are some traditional methods people use to control or what have we been doing. But where are we seeing the holes with this as well?
Yeah, I think right now, strategy used for management of cong worm, it depends on I think the first one, like you can use crop rotation, that's the best strategy and the cheapest strategy to manage con, rootworm like a con, solving rotation. And the second you can use likes liquid granular. I think in low project probably liquid insects can works a little bit better. But then in high project granular insects will be better. Another important way to manage traits.
Now most of the Western and northern cong worm have developed resistance to some of the BT traits. That's a major concern. I think the industry is developing some new BT traits in the near future. Should have allowed. Bruce, do you have anything to add on? The good news is that it's not good news, but western corn rootworm rootworm trade started in about 2005. By 2009, we started to see resistant western corn root worms in southern Minnesota.
That's pretty short duration for that trait to be completely effective. I think it speaks to that. Those worm population genetics are really pretty diverse. They've got a lot of ways to get around resistance. I talked about the Northern and crop rotation resistance, Westerns and BT resistance in Nebraska. They've got some per thid resistant beetles now, rot worms.
Now I think the good news is out of this whole thing is that for the most part we're getting reports of extended diapause or northern corn rootworm pressure. For the most part, the BT's seem to be working, but there has been resistance documented in North Dakota. We've had seen some resistant populations in Minnesota. And I think that's what we're really trying to keep our eye on right now is our northern getting around the BT's as well as the Westerns. Yeah, that's okay. Go ahead.
Okay. Yeah, have something to add low populations for Condor think it's if it's not necessary to use BT traits just avoid in this way we can help delay reducts and protect the technology for the future. That brings up a question too. It's like why do we see these shifting? Do you think with western corners, it seems like for a while that those populations were a lot higher, but now you're saying we're seeing more extended diapause, typically is with the northern corn rootworm.
Right. What's driving these shifts in what we're seeing out in the field like it seems are the populations the northern corn rootworm, are they going up now relating to these issues more? No, I think that's exactly right. The extended diapause trait has always been there. But when those northern populations are low, you don't notice it. When the northern populations are higher, it's not the whole population that has the trait. At least I don't know of any cases where that's true.
Maybe as high as 50% or around 50% will display the extended diapause trait. But if you don't have the Northern populations out there, you won't see the extended diapause. Now as these Northern have been increasing over the last few years, we're starting to see the extended diapause pop up and we're seeing it pop up in new areas. But as far as the BT resistance, insecticide resistance, those things, the root worms are basically responding to what we're doing to them.
They're adapting to our management strategies. That's why we need to use a lot of tools and be flexible. Like Fay mentioned, if you don't have a problem, leave it alone. Well, that's a good point because again, I know a lot of people haven't just planting BT hybrids, for example, to manage corn rootworm, but then some people have been layering insecticides. Are we still seeing lodging in these fields? Is that what you're saying?
We're seeing some of that pop up as well and should be using an insecticide planting when we plant a BT hybrid. No matter what to manage this, I don't know who wants to tackle that question first. But again, management is always the key question of what we can do to manage this pest. I'll try to tackle it first. You can chime in at the end here. But the problems for both northerns and westerns, I think those populations tend to increase in continuous corn extended diapause.
Northerns are not westerns. We don't have the root worms they do in the eastern corn belt that have lost their affinity to lay eggs and corn. So they'll lay eggs and soybeans and they get around to rotation that way. As far as rotation resistant root worms in Minnesota, as far as we know, it's only the Northern. But those continuous corn fields are ideal environments for both species. The populations build up resistance develops in those fields as well.
We do have some of these really high western corn rootworm population fields that have adapted to BT or resistant to BT. You do need a insecticide to help keep things going. Some of these fields are bad enough that really the smart thing to do is to rotate out of corn for a year. It gets a little trickier with the Northern and extended diapause.
You've got to be aware of what's going on, but definitely rotating out of corn for a year is going to knock those Westerns back and reset the clock in those fields. Yeah, that's correct. According to some studies, like if you do planting continuous in the field, if you have two species, Western and Northern Rum location, normally Western rum dominate. Be the dominant species and they will replace and has some competitive biology. The Northern um feel, Western um should be the dominant species.
And if you use car rotation, you can kill them almost one year and the next year you get back to con, that will be better. If a person has been doing continuous corn or even there haven't been rotated corn, how would they get a feel for their populations right now out in the field? What would you recommend that people do to see if they're having an issue out there? Obviously, scouting, but Okay. What would that scouting entail?
That you would recommend to be checking, see if they have an issue or not. You're definitely going to have to be in the field to know if you've got a problem or not. And you're going to definitely have to get into the field, not just on the edge, if you're just scouting the edge of a corn field, that's where beetles move in and out and those populations tend to be a lot higher there. They might be high on the first few rows, and once you get inside the fields, populations may be low.
Scout the field thoroughly. There's two ways, basically you can do it. One is to go into the field and do whole plant counts. Walk through the field, you look at two plants, you check for beetles in there. Check around the ears and then pull the silk spec. There's a link in the chat for some information on scouting. The whole concept is to scout the field thoroughly.
You don't have to waste a lot of time and whether you're doing the whole plants counts or you're hanging sticky traps out in the field. It's getting the field covered and scouting long enough in the season, But if you walk into a field and you've got Beatles all over the place, you really don't have to spend a lot more time there. You know, you're going to have to do some management of people are using the yellow sticky traps now.
But I'm going to caution them because the rootworm populations are variable, even within a field. And fa, and I, we're looking at roots from some corn rootworm studies yesterday. Even from rep to rep, that population varied and that's because the egg laying and the beetles populations varied. Even that small test area, they're real variable. Putting one or two traps in the field is likely to give you a completely wrong impression of what's out there.
How many sticky traps do you think they should have out there? Do you have any feel for that? And realistically because it takes time to do this, how often you have to check these and so forth? Do you have a feel for how many that person should put out in a field if they were going to put out sticky traps to monitor for corn rootworm? I can maybe answer that. It depends on how much detail you want out of that. If you're just trying to find high risk fields, you can probably get by four.
Some people try three that's getting iffy. If you're on the bubble and you're in that area where you're not sure if you've got a rootworm problem or not, then you need six to eight. And some studies Ken Oss lab did a few years back, the Northern's tend to need a few more traps to accurately assess the population, but I think most guys are just trying to figure out which fields are at higher risk.
You don't have to spend too much time out there, but you do have to do it for a longer period of time. And you're talking about 34 weeks, or because the Beatles are either moving into the field if they're late pollinating or later than other fields in the area, those sorts of things. Well, that's one question too that brings up what we're talking about, sticky traps. We do have a question that popped up here too. It's deals with root pruning there.
Again, do you recommend people about digging roots and since it is a drier year to do you think there would be more severe root pruning or would it be less? Or is it going to have more of an impact? Either. You want to tackle that question there and see what impact does the dry conditions having on root pruning this year? Do you want to answer that? I think you can ask it because we dry condition.
Okay. Yeah. I mean, if it's dry out but you know, because they're reducing the root system, that impact on yield is going to be greater. The other thing that happens when it's dry is especially if it's hot and dry, the roots don't regenerate as well, part of that's hybrid trait. But the damage in dry conditions or effect on yield dry conditions is usually worse. But the other side of that is that, you know, if it's dry and you don't have winds.
Um, you could have some pretty severe damage and it won't lodge. The other thing I want to point out is if you go into a field, you don't know if those beetles are coming into the field or leaving the field, or if it's extended diapause or not. Unless you look at those roots and see if there's a lot of root injury in that field.
That's one of the issues with rootworm beetles, especially the northern's are so darn mobile and they'll move back and forth between fields and even out of fields and feed on flower pollen and that thing and weed pollen on question also too. That comes up a lot of times. Now we're starting to see in fields or volunteer corns popping up through the canopy and soybean fields. What impact does that have on corn rootworm populations?
To again, at what point is it essentially that we're not rotating out of corn? Here again, we know that rotation can help overall with corn rootworm. But again, if we've got a lot of volunteer corn out there point, it's really not going to help us, right? Well, we did some work a few years back and looked at both Northern and western. And it doesn't really take that much volunteer corn relatively to pull beetles into the field to lay eggs.
I think if I remember the numbers right, it's only like 2,500 plants per acre or or you could have egg laying in that field. And that's not hard to do, especially when we have things like those wind events that came through a couple years ago, lodged a lot of corn and we had a lot of volunteer corn following it. I don't think they're smart enough to think of this all on their own.
But from the rootworm side, if you do have a lot of lodging, you have a hard time picking up some of that corn, and that creates more volunteer corn issues as well. Volunteer corn is not good. If it's out there till July, you've got larval surviving. And if it's out there pollinating later than everything else towards the end of the year, then you get a, you get beetles moving in and laying eggs. Here's a question that I did come in there too.
Have you noticed any plant or cover crops which promote predators of corn rootworm? Have either of you noticed anything about that? Is there any impact the having more cover crops out there might have on on populations of corn, rootworm and pressure? I don't know if it's the I mean the root worms don't really have that many predators. There's some nematodes that sort of thing. But what do you think about, you know, if you've got a cover crop out there, keeping that soil, minimizing bare soil.
I don't know if that would help on egg laying or not, but I don't think I have seen anything published about it. Yeah, I simply has no study about lack the prep the crop on cidal management. I think the impact of the cover crop is going to be what that does to corn growth and root development. Those moisture, those things, Yeah, provide nutrition for the corn development. Related to that question that we did come in earlier as well.
They ask about beetle bombing, probably not your favorite, but if they do it, what's the best timing? Because if they see a field, for example, with a lot of beetles out there, a lot of people panic and want to spray beetles because they think they're clipping their silks and the corn won't. Pollinate. That's actually pretty rare. After that corn is pollinated, you can pull the Usse back and shake the ears, and if the silks swall off of those kernels, they've been pollinated.
But a lot of that silk clipping actually happens after the pollination is all done. That's a whole separate reason for putting a foliar insecticide on for adults. And for the most part, it's actually pretty where you have those levels of 5678 beetles per plant. Then your corn isn't pollinated yet and your silks are clipped within to the tip of the ear.
Some guys can't rotate or won't rotate, and they don't really have a good way to put insecticide on a lot of guys that have tried to resort to beetle bombing or spring the adults to prevent egg laying. The threshold is one beetle per plant, but a lot of guys are doing it too early. This control would go on after the silk clipping and pollination is done. For the most part, you're talking about one beetle per plant. You want about 10% of those beetles to be. Females to be pregnant.
So you can see the swollen abdomen swollen with eggs. And you're probably going to have to scout, scout every ten days or so for a while because like I said earlier, those beetles don't all emerge at the same time and they move in and out of field. And your insecticide residuals only so long, one beetle per plant, 10% ravage females, and then check the field in seven to ten days. And keep doing that. Then you might have to put another foliar application on. Usually that's the case.
Here's, here's one more question that came in earlier with registration as well too. So you talked about a lot of management again, how do we best prevent resistance and maintain the effectiveness of the BT trades overall guidance there that you would offer? Yeah, I think as I mentioned before, using trades as necessary if it's your project is low in your field, it's not necessary to using trades.
First, you can avoid a resistance problem in the future and the second, it will save you a lot of money for buying those BT traits. The second thing, if you see any problem earlier, you can use other insecticides, different traits, different mechanisms to avoid insect developed resistance to one model of action. If you use multiple model of actions that can slow insect resistance.
Also I think right now because of the problems, especially for Western condom, they have resistance to almost every BT traits in most of the locations in the future. I hope the industry can have some, we can have some new model of actions. One they're using right now is NI plus BT. And that can, your insect project is low in the field, but if your insect project is high, because I is working totally different, competitive BT, they kill insects very slow.
It takes a little bit of time, normally for BT. They can kill the insects one or two days, but I takes about like more than five days to kill the insects. That relates straight to a question that just came into it says, what are you seeing hearing about the new traits efficacy? I'm assuming that they're talking about the RNAI technology. If you want to share a little bit about if people aren't that familiar with how that works.
And again, what's the efficacy of that you're seeing compared to say, the BT traits? Well, it's another mode of action and it's a supplement to the BT. But as Fay mentioned, that BT has to be functioning to a certain extent because if the insects are resistant, the larva are resistant to BT, they're able to feed. They could do quite a bit of root damage before the RNI can kill, kill a larva.
I have seen some fields this summer where they put the RN hybrids under extremely high rootworm pressure and there's problems log a lot of root feeding and lodging. I think the seed companies will tell you too that if you've got really high pressure it's not going to answer everything, but it will help under moderate and lower pressure where you're dealing with BT resistance. It's a good tool but it's not bulletproof, just like any of the other tools.
I'll just reemphasize that if you want to help root worms out, you just keep doing the same thing over and over again in the field. And they'll figure a way around it pretty quickly. And here's another question. Is there any non BT resistance or tolerance out there? There's differences in hybrids and that sort of thing. But I think one thing that growers should, can look at, the root system of those hybrids themselves. Something that's got a larger root system maybe regenerates.
That'll help you out if you're in these high pressure situations or worried about root worms. That's something I'd always look at right in the beginning, is don't pick a small T hybrid. It's just making your life more difficult. Here's one more question that popped up saying if you mentioned already, but northern corn rootworm being found in new areas of the state, are there any particular region and counties that appears to be heading into versus where they're regularly prevalent?
Where are you seeing the issues? I guess they issues. It's real localized and there's no reason to its spills. Not repealed in an area either. This problem has been here in the early '80s, disappeared as northern populations declined. It came back in the early 2000, disappeared, now it's coming back again.
There's pockets in south central Minnesota and that Martin County areas one little bit up into Brown County, I've seen some fields in stream, southwest Minnesota, but it's not quite as big a hot spot but they're seeing up in Douglas County, I think into Otter Tail, some areas where they haven't seen extended diapause before. They've had Northern corn rootworm pressure up there before.
One thing I didn't mention as you go north because the eggs are more coal tolerant, you see more Northern corn root worms. But even in southern Minnesota, at one time, the Northern were the dominant species. It's fairly recent since the Westerns became more widespread down here. I should note that you both have written a really great article that's available on the Minnesota Crop News if people want more details on that. That has been posted online, was posted earlier this week.
There's a lot of great resources on our extension crops website. We will have those links close to this recording as well or you can find it on our strategic farming website. For anybody listening to this recording, I did want to ask you a quick know that you're also working with European Corn Board. Do you have any thoughts you wanted to mention about that as well too, because we can't totally forget about that test either. Yeah, like European combo has been a historic insects here.
But because of using the BD treats, it works very fantastic to targeting the species. But right now, I think two years ago in Canada, they found some species European combo showing resistance to or proteins in Ohio state. They're working on some research. They found resistance in Northeast US showing some resistance of European combo to there proteins. The high chance European populations will come back in Minnesota and showing resistance. That will cause a big problem for us.
The only thing right now we want to understand and to do some survey understandability of these insects to the current BT technologies that will help us a resistance management. If you find any infestation of the European combo in your field, please did I can go and collect some populations and test it against the current BT traits. That will help a lot for future research. All right. Excellent. Thank you Bruce. I know you got like about 1 min here.
Anything you want to add? About time, year, sleeping, aphid, spider mites. We've got dry conditions. Spider mites, we'll probably revise older news article. We're starting to get some calls in these drier areas on spider mites. There has been some treatment going on for a few weeks in little pockets.
We did get some rain in central Minnesota, and I think not so much rain, but if we can get some cooler temperatures and we can get leaf moisture even with heavy, get that for a couple of nights in a row, Hopefully we can get some fungi going to knock those populations back. But ads are going to be moving around the country here pretty quick as soybeans quit growing vegetatively. Both of those insects or ones And insects, both of those are something to scout for here in the next week or so.
All right, and stay tuned because that will be something we certainly can adjust here on our upcoming field notes sessions as that anything progresses there. And also, I'm sure you'll have stuff out on the Minnesota crop news as well too. But again, I'd like to thank our guests, Dr. Feng and also Bruce Potter today, and all of you for attending our extension field notes session today.
And also, of course, like to thank the Minnesota Soybean Research and Promotion Council and the Minnesota Corn Research and Promotion Council for helping make these sessions possible. Have a great rest of the day, and I hope to see you next week.