After the flooding - crop disease & weed management considerations
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 8 AM on Wednesdays throughout the cropping season. During the live webinar, participants can join in the discussion and get questions answered.
Ryan Miller:An audio recording of the live program is released following the webinar via podcast platforms. Thanks. And remember to tune in weekly for a discussion on current cropping and crop management topics.
Liz Stahl:Welcome today, and these sessions are brought to you by Extension and also generous support from the Minnesota Soybean Research and Promotion Council and the Minnesota Corn Research and Promotion Council. And just a little bit of background on the session today. I was just reading Mark Seeley's weather report, you know, saying most or many climate reporting stations, it was the wettest June, but also statewide for Minnesota. This was the wettest, April through June time period in state history. So we've had a lot of rain in a lot of areas, especially looking at, you know, northeastern Minnesota and then southern, especially across southern Minnesota, but we've all been affected by excessive rain, a lot of flooding, replants replants getting replanted, and so far as in soggy conditions.
Liz Stahl:So, we hit on the nutrient management topics, last week and some planning options, including cover crops. This week, we're gonna look at after the flooding, crop disease and weed management considerations. So, again, I'm Liz Stahl, extension educator out of the Worthington Regional Office, and I'm really excited to, introduce our guest today. We have doctor Alison Robertson. She's extension field pathologist with Iowa State University.
Liz Stahl:And then doctor Tom Peters, he's a weed scientist and extension sugar beet specialist with U of M Extension and North Dakota State University. So with that, I will turn it over to Alison. And, again, she's been dealing with a lot of the same issues we have in Iowa. But, again, if you wanna kinda share your thoughts and what should we be looking out for, and is there anything we can do about it?
Alison Robertson:Hi, Liz. Thanks very much for having me. I'm always excited to talk about diseases. So, and, yes, very wet conditions. So, especially the excessive precipitation that we've had and then also the flooding is gonna favor different diseases in our, soybean and our corn crops.
Alison Robertson:I'm gonna focus on those 2 crops. So if we start with soybean, flooded conditions obviously favor things like the OMI seeds, so Phytophthora, also Pythium. If they were you could have run into problems with Pythium damping off in some of those later planted fields, we also need to be watching out for Phytophthora stem and root rot, especially later on in the growing season. Particularly if it dries up, you might notice random plants in your fields dying. So what you wanna do is look for that chocolate brown lesion, of Phytophthora.
Alison Robertson:We are seeing that the Phytophthora populations are evolving and are overcoming a lot of the resistance genes that are being used in commercial soybeans. So, yeah, look for that. Darren Mueller, my colleague here at Iowa State, wrote a, ICM newsletter on white mold and SDS and things to look for there. So that link is in the in the chat for people. And, also, if we think about SCN, which, of course, is the number 1 disease on soybeans, Greg Tilker wrote a blog about, well, how flooding will affect soybean cyst nematode.
Alison Robertson:The bad news is or, yeah, the bad news is that, those, worms, can survive flooded conditions for several months. So, the flooding is not gonna decrease that, but it will slow down their reproduction rates, which should slow down the numbers that are increasing. So I would encourage, folks on the call if they're worried about SDS white mold or soybean cyst nematode to read those couple of blogs. If we move across to corn, so with flooded, the first thing that I think about with flooded corn is, we could see some crazy top out there. So crazy top is often a problem after flooded conditions.
Alison Robertson:Usually, it's just scattered plants in those in those areas that were flooded, and those plants will be barren so they won't produce an ear. So there could be a reduction in yield depending on how many of those plants are affected. Other things that to think about would be physoderma. So, remember, physoderma causes brown spots on the leaves, which, we don't think, reduce, yield. So that's good news there.
Alison Robertson:But look out for things like Physoderma node rot. Some hybrids are particularly susceptible to node rot. These hybrids are not usually susceptible to brown spot on the leaves. So, there's a link in the, again, for you to a blog that I wrote on about that. And then a a lot of times with, a lot of heavy rain, we see Goss's wilt developing just because that heavy rain bruises the leaf tissue and allows that bacterium to get in and infect the plants.
Alison Robertson:So if you're growing a, a hybrid that's susceptible to Goss's wilt, you could see some some Goss's wilt. So those are the kind of diseases that I think about with flooding. As we move forward, in the growing season, we do have a lot of moisture around, and so we could see some foliar diseases developing, like frogeye on, soybeans, particularly if you're growing a susceptible variety. On corn, I would think northern corn leaf blight, and perhaps tar spot, particularly because you're gonna be a little bit cooler than we are down in Iowa and maybe some gray leaf spot. When you're thinking about management, it's only those foliar diseases that I've just mentioned, the frogeye and then the northern corn leaf blight, gray leaf spot, and tar spot, that we can do anything about during the growing season.
Alison Robertson:We can go out there and apply a fungicide if we're if we're seeing those diseases. I always encourage growers to check the resistance of those hybrids to those diseases because a lot of the hybrids have pretty good resistance, and so you could probably sneak by without a fungicide. But if you are growing a more susceptible hybrid or variety, then you might wanna consider a a fungicide for that. The stem and the root rot diseases, the Gossel's world, the Pfizer derma, the CrazyTop, there's nothing you can do about now, couldn't do now this growing season. But, 1 thing that I would encourage you to do is to scout scout your fields.
Alison Robertson:I know I'm the exception to the rule. I love being out in fields and scouting for disease. I know that, you know, a lot of folks probably don't enjoy being out there in the hot pollinating corn. But, the reason why you wanna get out there and scout for disease, you know, stop the I was talking with Phyllis earlier. We wanna stop the track.
Alison Robertson:We wanna get out of the track, walk beyond those end rows, and, check the field to see what diseases are present in that field. Make a note of those diseases because that's gonna help you, with your hybrid and your variety decisions when you next come back to that field. Remembering remember that every time we have a disease in there, we're building up that inoculum and, for all of these diseases that I've talked about, they all survive in the soil or in the crop residue. And so as we build up inoculum, we just, lengthen that side of the disease triangle right, and so we get a if we get the right environment and we have a susceptible host, then we're getting a bigger triangle. A bigger triangle means, more disease.
Alison Robertson:Right? So, I think I covered that all. I really zoomed through it. But
Liz Stahl:No. A lot lot of great information. And, you know, the fungicide question was 1 thing that I was wondering about as well. So, again, not all these diseases are gonna be controlled by a fungicide. Right?
Liz Stahl:And and, you know, I just wonder some of these areas if we're looking at have you done some economic analysis too of of these products? Because we might be looking at some reductions in yield, put yield potential this year too with, you know, delayed planting or just, you know, there could be nitrogen deficiencies out there, inability to get timely herbicide applications, things like that. I was just wondering if you wanna share some thoughts about that.
Alison Robertson:So, yeah, I mean, it's really important to think about that return on investment, right, when you use a fungicide. And I I know that, crop protection network dotorg is, working on a decision tool for return on investment on fungicides, and, hopefully, it'll be out within the next few weeks, but it's not available now. But, yes, if you're thinking about, putting on a fungicide, think about the cost of that fungicide, the cost of the application, and then, you know, what your your grain price is gonna be and, you know, thinking about if you've, planted late, how's that gonna impact your yield potential? If you're if you're running out of nitrogen from the flooding, you know, just remember that a fungicide is there to, protects the crop against disease. Right?
Alison Robertson:It's not gonna help that crop take up nitrogen better, survive the flooding better, you know, overcome the late planting effect. A fungicide is there solely to protect that plant from disease. And, yes, sure, I know that there are physiological benefits associated with the QIIs or or the strobilurins, but, those benefits are very hard to define. And they're they're definitely affected by genetics. And, so it's it's it's just hard to put out a fungicide for a physiological benefit, you know.
Alison Robertson:Mhmm. You should be putting them out for disease management and that's and we have shown time and time again, you know, corn pathologists across the US have shown time and time again that if you're putting a fungicide out for disease management, you're gonna get a return on investment for it. You know, if you're pulling it out just for a plant health benefit, then then you're gambling. So play it out.
Liz Stahl:Yeah. That's and that's excellent points to make too. And I, you know, I just wondered too when we've had some later planting dates, you know, have you 1 of the things we always say is, oh, or hear people say is that fungicide might help keep the plants greener longer. Well, if you have a late planting date already, do you really want that? Delayed harvest rate?
Alison Robertson:Yeah. Yeah. That's a really good point. And, I mean, I agree that a fungicide will keep the plants greener longer, but, yes, if you throw in that that late planting yeah. And remember that tar spot loves green tissue.
Alison Robertson:Right? And so it's gonna it's gonna yeah. I mean, it would be interesting to look at we know that with plants, planting date will affect, disease severity. So later planted crops are more are more, likely to get disease just because we're now running into that more favorable conditions, July August, when it's warmer, higher humidities, and so that's gonna favor disease and we're just starting our grain fill period, you know, later on. And and so we if we're gonna get disease, we want it to develop as late as possible during grain fill.
Alison Robertson:And when we late plant, then our grain fill starts later, and so we get disease developing earlier in the grain fill, if that makes sense.
Liz Stahl:Mhmm.
Alison Robertson:So, yeah.
Liz Stahl:Yep. No. Good points. And we did have a question about any stock diseases found this year so far. I know we've got quite a range and maturity of of, you know, or, you know, where the crop stages are.
Liz Stahl:But, yeah, just wondering about likelihood of them showing up with too much moisture with stock diseases.
Alison Robertson:I I think that's a good question. And, yes, I mean, stalk diseases are associated with some kind of stress on the plant. It's likely that because of the wet conditions, we could have got, like, more, root infection and root rot, and so that could develop into store rot later on. We there's no store rot showing up now this early. I haven't heard of any any store crots, showing up this early.
Alison Robertson:Really, the ones that would show up would be Pythium or or, bacterial stauchrot. But those, you know, anthracnose, gibberellae, fusarium, they're all gonna show up later during the growing season. Gibberellar could be a problem. And, yeah, we just kind of have to wait until r 4, r 5, and then, just evaluate the health of the the crop then. So
Liz Stahl:Yep. Nope. And, and think about that at harvest too. And I know you have, there's a resource sheet and that will be, you know, if you're listening to this on the podcast, you can find that on our website. But then those of you joining here live, we've got, in the chat a link with has resources, and that has a lot of links to the identification, resources too for all these diseases.
Liz Stahl:But alright. Well, thank you, Allison. We'll come back to you at the very end here to wrap up if anybody has any more questions too, but we will turn it over to Tom Peters here and just, see on the weed management and too because, yeah, it's certainly been a challenge to get things out there. We've had a lot of rain.
Liz Stahl:Our our pre herbicide's still there. What if we weren't able to put our post herbicides on? Just kind of a whole lot of things going on.
Tom Peters:What a year, Liz. What a year. You know, I I've been, doing this now for 30 or 35 years, and I've been waiting for the perfect year. And, unfortunately, 2024 isn't going to be the perfect year. So, you know, we we have the the situation that we have, and we have to find a way to get through it.
Tom Peters:So and weeds, unfortunately, are part of it. So what I'd like to do is spend a few minutes and and, talk about strategies for managing weeds, maybe weeds that are bigger than they should be, maybe other options to herbicides, if any, exist. And then if we have time, Liz, I think we need to get to talking about the drowned out areas, how we're gonna manage weeds in those areas. And, my perspective, I wanna make sure everybody knows this. I'm based in Fargo.
Tom Peters:I support sugar beet growers. So my travel is north of Highway 212. So, I cover that area all the way up to the Canada border. So, Liz, on anything, any perspective south of 212, you're gonna have to help me out on that 1 because I don't get down that far.
Liz Stahl:It's, like, wet. Okay.
Tom Peters:So the first thing I wanna do is I wanna talk about weed biology. We have a lot of respect for weeds, and some of the characteristics of weeds, I think, are more important in 2024 than ever. So the first 1 is and we, as educators, we like to use a chart that indicates what weeds are gonna germinate first during the season and then the progression of weeds, germination, and emergence through the year. So, we usually start with kochia, and then we end with the pigweeds that seem to start emerging in May and emerge through June July. Well, throw that slide out the window.
Tom Peters:It doesn't apply to 2024. And the reason for that is is our soil temperatures are still relatively cool. I would argue we still have May soil temper temperatures. So what I've observed is a longer window of weeds germination and emergence. Kotia, common ragweed, lambsquarters, they're still germinating and emerging, and that's causing some challenges for us.
Tom Peters:The other thing that I've noticed is there's different weeds in this wet, cold environment than what we normally see. So an example is smartweed. I hadn't seen smartweed for several years. This year, I'm starting to see it germinate and emerge. I don't see a lot of nightshade.
Tom Peters:I'm seeing nightshade. Barnyard grass is all over the place, and it's a predominant wet weather grass that we have. And there's even a few people that have talked about burr cucumber. And I know we have burr cucumber every year, but it's a little more wide spread this year than others. And then, of course, there's still yellow nutstedge as well.
Tom Peters:So weeds that are germinating for a longer duration of time, and they're different. The third thing I wanna mention, Liz, is I don't think our post herbicides are working as well as they normally do. And some of that's on the herb 1 of the frequent 1 of the frequent, calls I got was weeds aren't dying. And my answer was, it's so dry. They've developed a thick cuticle.
Tom Peters:They're just not taking up herbicide. Well, now, in 2024, we don't have that issue with cuticle. It certainly isn't dry, but weeds aren't growing. They're not growing, so they're not taking up herbicide. An example of that is lamb's quarters, control with glyphosate.
Tom Peters:So that should be relatively easy. 1 spray, maybe 2 maximum, should control lamb's quarters, but I've seen a lot of lamb's quarters escapes this year, certainly with Liberty, but also with Roundup glyphosate products, because these weeds just aren't growing, they're not, they're not taking in herbicide, and unfortunately, they're not dying as a result. So what do we do about it, Liz? What are we, what are some of the strategies? I would say in general, weeds are probably larger than we'd like them to be, mostly because we haven't been able to get sprays on timely.
Liz Stahl:Mhmm.
Tom Peters:I think we've got to look at tank mixes. Okay? So depending on the trait that you have, the crop that you planted, I would look for a tank mix partner with with, your your primary herbicide. Now you have to be careful though, because I talked about the weeds not growing, well, the crops aren't growing very good either, and, that means they're not metabolizing herbicide. So, that means, potentially, these mixtures might be more susceptible to herbicide injury than than other years.
Tom Peters:Some of you have, used soil residual herbicides post to the crop and preemergence to the weed. In sugar beet, we call that lay by. So they're the chlorosetamide herbicides, there might be some triazines, maybe even a PPO inhibitor herbicide. And I think the question is is should we still use some of those soil residual herbicides? And and, Liz, I think the answer would be, well, it probably depends.
Tom Peters:It depends on which 1. If you're using the chloroacetamides like Dual or Outlook or or Warrant, I think they are still very much in play. The triazines, metribuzin, atrazine, I would be really careful with that because, ultimately, this is about not only what we're doing this year, but what we're planning to do in next year's crop. And I'm starting to be concerned already about herbicide carryover. Mhmm.
Tom Peters:So last year, Liz, it was because it was so dry and and so hot. Microbes need water and they need heat, but not excessive heat. This year, we have plenty of water, but, unfortunately, microbes don't swim. They don't like waterlogged soils. So our our, lack of degradation might be from cold saturated soils.
Tom Peters:So you have to be very careful about the products that you're using, late in the season, and be concerned about your your your strategies for what you're gonna do on 2025. Any thoughts, Liz? Anything you'd like to add?
Liz Stahl:No. Those are excellent points, and that's the thing. I mean, we look at the calendar. 1 of the comments here too is, yep, July 4th. We're supposed to be halfway through the growing season.
Liz Stahl:We still have some areas. Maybe people might try to plant some beans yet, But, but, yeah, it you know, here we are in July. And so you think about what the rotation restriction on Flexstar and and these other products. You know, you brought up a good question about, crop stage. You wanna comment on that a little bit too because a lot of our products have restrictions based on crop stage and crop height.
Liz Stahl:You know, even though it's slower growing, you know, where are we at, you think, with crop stage?
Tom Peters:It's on and it's unfortunately, it's all over the place. Our fields can and let's just pick on corn for a few minutes. We could have, we could have 4 leaf corn, so corn that's down by your ankles. And then in other parts of the field, we could have corn that might be as high as as waist high already. So these challenges with all these different growth stages in the same field, I think, is is adding to maybe the complexity So, So, those are important.
Tom Peters:In sugar beet, most of our rows are closing, and that signifies really the end of the weed control season. And there's a lot of limitations that we have on application, because we have to be concerned about preharvest intervals for products, before before we start our preharvest.
Liz Stahl:Yeah. That's that's exactly right. And, you know, we've had some questions here. You know, again, what about drop nozzles in corn? Do you have any comments about that?
Liz Stahl:It's pretty much a rescue treatment and and carryover. Yep. Starting to be a big factor.
Tom Peters:I don't have a lot of knowledge about drop nozzles. So, maybe you have more experience with them than I do. I I don't, Liz.
Liz Stahl:Yeah. I guess that's something too. I would just make sure you're reading the herbicide label for any restrictions. Because like you said, Tom, our I know our crops down here, there's some fields. It's just it's just all over the board depending where it's at.
Liz Stahl:Just a lot of more unevenness, and that's showing up. You know, as a corn supposed to be renting entering that rapid growth stage, we're getting a lot lot more unevenness. So I would just say, you know, really look at the the herbicide label for those restrictions and make sure you're you're following that. We've got some general comments here about how late can we replant soybeans, you know, usually and I'll just throw in a couple comments on that. Yeah.
Liz Stahl:Usually, we say up to July 4th roughly, so that's tomorrow. But then we go at least to a relative maturity unit earlier. If you go way earlier, you can kinda mess things up too. So, I mean, we're getting in that window of tough decisions. If if you still have water standing in the field and more rains on the way, you might want to be looking at some other cover crops.
Liz Stahl:And maybe that's something you want to touch on here too because we are getting past that point where we can really do much, but we still need to have weed control on these jaun out spots. Any comments you wanna share on that, Tom?
Tom Peters:Absolutely. So so I think we have to play the long game, and that's what about next year and the year after and the year after? Ignoring the edges of fields or the drowned out areas is going to reset the clock on weeds, and and we're gonna add more seeds into the soil seed bank, and that means, we're for some of these, we're gonna have to fight them another 4 to 6 years, and we certainly don't want that. So I would I would really encourage our audience to proactively manage the edges of fields. You and your neighbor have got to decide who's gonna manage the fence line.
Tom Peters:So you've gotta manage those weeds, and then in the drowned out areas, I would encourage you to use, various mixtures, valor sharpen 2 4 d, maybe some clarity, roundup, use some mixtures drowned out areas and fields. Don't allow them to go to seed. Yep. Good point. And and just quickly here too, we're
Liz Stahl:getting a lot of growth and development questions. We'll try to hit in a second. But do you have any recommendations for, like, these any rescue treatments, any go to products you you think are tactics that we could use? Again, looking at the calendar and and, where we're at here in the game.
Tom Peters:Well, like you said a few minutes ago, we still have to follow the label. And, you know, I'll I'll use an example of the label. The Liberty label indicates when we should be finishing application of of, Liberty and Soybean, and and that's at the end of flowering. And, I think in some parts of fields, we're probably at flowering right now. We're seeing the start of those.
Tom Peters:So it's it's a hard question to answer, mostly because of the what the what what we have to follow in the labels and these different growth stages that we have in fields. I think that's where our regional educators can can help, especially, in location specific areas and and help our audiences.
Liz Stahl:Alright. And, again, I know we've got a lot of general crop management, questions here too, so maybe I'll put that on hold here for a second. But, Allison, is there anything you wanted to share? Because we're coming at the end of our time here, or you, Tom, too as well. But first, I'll turn it over to you, Allison.
Alison Robertson:Yeah. I mean, I just wanna say thanks for having me. And, if anybody has further questions, they're welcome to send me an email. My email is alison r. Remember, I have 1 l in my name.
Liz Stahl:Yeah. I forget that sometimes when I try to email you. Sorry. But
Alison Robertson:It's okay. Alias0nr@ia state.edu. But, thank you for having me.
Liz Stahl:Hey. We appreciate having you too. And I I get that there's no e in the front of my name either, and that's been a curse for my entire life. Thanks, mom and dad. But, but anyway, yes.
Liz Stahl:So, again, we appreciate you being on, Tom. Any last parting comments again? And I think we'll handle these general ones here in a second if people don't mind hanging on.
Tom Peters:So I I have a comment or 2. You know, we've been focusing a lot on herbicides. So we can't get in and use the inner row cultivator because it's too wet. And in some cases, the weeds are too big. So, I think there's gonna be some limitations there.
Tom Peters:But, you know, it might be a good year for the weed zapper, especially if our fields start to dry out a little bit and our weeds start to grow, these wet conditions should be the perfect environment for using the weed zapper if anybody has access to though that equipment.
Liz Stahl:Yeah. You've done some really neat work with that. And I do wanna add dummy back to doctor Robinson Robertson here too. I know you've got some really great articles online too about crop diseases and great research. I encourage people to check that out.
Liz Stahl:Hey. We work with other people's stuff all the time. I know we have a lot of resources on our extension website too for the U of M, but you've just written some really nice articles recently too. But yeah, I know we're getting to the end of the time. I will, wanna thank our sponsors again, the Minnesota Soybean Research and Promotion Council and the Minnesota Corn Research and Promotion Council.
Liz Stahl:Again, thanks for joining us today.
