Drought's Impact on Weed Control

Michael Sindelar Author

10/01/2020 Added

1 Plays

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In this episode of the Nebraska Cropwatch Podcast, Michael and Amit Jhala talk about weed control. The topic of this conversation is how the drought is affecting chemical control of weeds.

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[00:00:00.544](gentle music)
[00:00:02.960]Welcome to CropWatch Podcast,
[00:00:05.410]a production of Nebraska Extension.
[00:00:11.780]Welcome to The CropWatch Podcast.
[00:00:14.940]I'm your host Extension Educator, Michael Sindelar.
[00:00:18.940]Today, I'm gonna be joined by Dr. Amit Jhala.
[00:00:23.840]And we're gonna be talking about herbicides
[00:00:27.120]and weed control for the season.
[00:00:29.100]Hi Amit, how are you doing this morning?
[00:00:31.260]Doing very Well.
[00:00:32.140]Michael, how are you?
[00:00:33.200]I'm doing great.
[00:00:34.400]So have there been any issues with carryover
[00:00:37.700]from the previous seasons herbicide
[00:00:40.170]causing issues this season?
[00:00:42.410]Yes, particularly this year,
[00:00:44.630]we are seeing some carryover injuries
[00:00:46.600]of a fomesafen based herbicides
[00:00:49.340]applied last year in soybean,
[00:00:51.580]and this year we are seeing
[00:00:53.180]there are carryover injuries in corn,
[00:00:55.510]as well as some HPPD inhibiting herbicides
[00:00:59.590]for example, mesotrione based herbicides
[00:01:01.710]were applied last year in corn postemergence,
[00:01:05.090]and then we are seeing some injuries in soybean this year.
[00:01:09.530]And this is particularly because last year,
[00:01:12.850]Mike if you remember, there was early season flooding
[00:01:16.290]and then continuous rain.
[00:01:18.210]So growers were not able to plant on time.
[00:01:21.750]So planting was really delayed
[00:01:24.100]and I know some planting was made in end of June
[00:01:28.070]or even in July,
[00:01:29.360]some growers were planting their corn and soybean.
[00:01:32.560]So when planting was late crop growth
[00:01:35.010]and development was late last year
[00:01:37.240]and also the herbicide application was very late
[00:01:41.000]in the season, that generally, for example,
[00:01:43.600]postemergence herbicides we apply in the month of June,
[00:01:47.250]if you plant by the end of April or early May,
[00:01:51.270]but last year, some growers
[00:01:53.350]were even applying postemergence herbicides
[00:01:55.990]by the end of July or sometimes in early August,
[00:01:58.830]because planting was late.
[00:02:00.630]And this year it was completely opposite.
[00:02:03.060]The early spring was very great.
[00:02:05.680]Temperature was high in the month of April,
[00:02:07.920]so majority of growers were able to plant
[00:02:10.940]their corn and soybean by the end of April
[00:02:13.990]or even they started very early in the season,
[00:02:16.400]like the first week of April
[00:02:17.810]and they were almost done by the end of April.
[00:02:21.020]So that created some issues with reduced planting interval
[00:02:26.437]between last year's postemergence herbicide application,
[00:02:28.950]which was late
[00:02:30.220]and this year planting was early.
[00:02:32.250]So that created some issues of reduced planting interval
[00:02:35.730]and certain herbicides,
[00:02:37.010]for example, fomesafen based herbicides
[00:02:39.580]applied last year in soybean
[00:02:41.820]may require 10 months of planting interval,
[00:02:47.160]between applying herbicides last year
[00:02:49.880]and planting corn this year.
[00:02:51.230]So that planting interval was not maintained
[00:02:54.040]and that has created some issues of carryover
[00:02:57.820]herbicide injuries this year in both corn and soybean.
[00:03:01.480]Amit can you tell us what
[00:03:03.060]those herbicide injuries looked at
[00:03:04.940]and roughly when they were expressed in the crop?
[00:03:07.060]'Cause I'm guessing that some of those
[00:03:08.122]would probably been a lot earlier in the season
[00:03:10.310]than where we are now.
[00:03:11.970]Or are we seeing some of those symptoms popping up now
[00:03:14.870]or being exaggerated now?
[00:03:16.800]Yes, if you see fomesafen carryover injury in corn
[00:03:20.700]would look like little bit of yellow strip
[00:03:24.700]on the leaves of corn plant
[00:03:27.230]that are typical symptoms of
[00:03:29.360]fomesafen carryover injury in corn.
[00:03:31.890]And in soybean,
[00:03:33.840]particularly with HPPD inhibiting herbicides,
[00:03:37.970]you will see some yellow color leaves of soybean
[00:03:41.270]and then sometimes a little bit of white bleaching
[00:03:45.610]you will also see on the new growth of soybean.
[00:03:48.620]So those are typical symptoms of both of these herbicides
[00:03:53.100]with carryover injuries.
[00:03:54.660]So you talked about how dry and warm this spring was
[00:03:58.900]to help get an early planning start,
[00:04:01.520]there's part of the States that have barely received
[00:04:04.270]three inches of rain since planting
[00:04:07.890]rolling into a drought.
[00:04:09.050]How is that affecting herbicides
[00:04:10.920]and how effective those herbicides are?
[00:04:13.710]And then the last part, I'm sorry,
[00:04:15.830]multiple part question.
[00:04:18.470]Are there options to make your herbicides
[00:04:20.300]more effective during a drought?
[00:04:22.490]In last three years, drought was not an issue,
[00:04:25.870]but this year we haven't received much rain,
[00:04:29.880]particularly in the end of June and in July,
[00:04:34.270]basically at least in South Central Nebraska,
[00:04:36.860]we haven't had rain in last three to four weeks from now.
[00:04:41.160]So that has created some issues,
[00:04:43.500]particularly with performance of postemergence herbicides
[00:04:48.610]when weeds are under stress, even if it is a water stress,
[00:04:52.290]for example, that is what we are seeing right now.
[00:04:55.110]Waterhemp and Palmer amaranth are under stress
[00:04:58.150]because of a lack of moisture.
[00:05:00.680]And so when weeds are under stress
[00:05:03.350]and if you apply postemergence herbicides,
[00:05:05.570]then overall absorption and translocation of the herbicide
[00:05:09.410]do not occur very easily.
[00:05:11.690]So the plant or herbicide will not perform very well.
[00:05:16.340]So this year, even in some of our research plots,
[00:05:19.760]certain herbicides are not performing well
[00:05:22.520]and that is I believe because of response of weeds,
[00:05:28.070]due to water stress condition.
[00:05:30.600]And that's why we are seeing less than expected weed control
[00:05:35.330]this year, particularly when those herbicides were applied,
[00:05:39.090]when plants were under stress
[00:05:41.010]and they were not growing healthy
[00:05:43.650]and that affects absorption and overall translocation
[00:05:47.300]and performance of herbicide.
[00:05:49.610]And this is true for any type of stress basically
[00:05:53.200]and water stress is, one of them.
[00:05:55.780]And in fact am also getting questions from growers like
[00:05:59.147]"My x herbicide is not working well
[00:06:01.197]"and it looks like I didn't apply...
[00:06:02.887]"Or do you think I have this herbicide resistant weed?"
[00:06:07.000]But in most cases, either those herbicides
[00:06:10.060]were applied when weeds were too tall
[00:06:12.030]to be effectively controlled
[00:06:13.740]or number two,
[00:06:14.950]they were applied when weeds were under stress,
[00:06:17.550]particularly water stress and that's why
[00:06:20.170]the herbicide performance has been reduced.
[00:06:23.010]So for the best performance of postemergence herbicides,
[00:06:27.330]we generally recommend like better you wait a few days,
[00:06:30.880]or if you have ability to irrigate your field,
[00:06:34.150]then maybe better you irrigate the field first
[00:06:37.240]and let the plants to grow healthy and then apply herbicide.
[00:06:42.800]But you also again need to make sure during this process,
[00:06:46.470]the weeds should not grow too tall because again,
[00:06:49.380]otherwise your herbicide would work better
[00:06:52.040]but because you apply that too late,
[00:06:54.950]that may also reduce the herbicide efficacy.
[00:06:58.160]So you need to be careful like don't wait too long
[00:07:01.070]and apply herbicide when plants are healthy
[00:07:04.710]and growing well.
[00:07:06.310]Plus including all the labeled adjuvants are also important
[00:07:10.420]because it helps with the absorption
[00:07:13.740]of those herbicides in the plant.
[00:07:15.560]So adjuvants are very important,
[00:07:18.610]particularly ammonium sulfate and some crop oil concentrate
[00:07:23.240]and methylated seed oil or non ionic surfactant.
[00:07:27.050]So based on label, which one is labeled with
[00:07:31.040]those type of herbicides.
[00:07:32.570]But again,
[00:07:33.590]you should not add ammonium sulfate
[00:07:35.580]with dicamba based herbicides,
[00:07:38.200]applied particularly in soybean
[00:07:40.460]because those are prohibited and if you do that,
[00:07:43.620]it increases the volatility of dicamba.
[00:07:48.310]Great, well, you brought it up, dicamba.
[00:07:52.520]what are our options to replace dicamba,
[00:07:54.870]if it's not gonna be on the market
[00:07:56.260]for use in soybeans next year.
[00:07:59.490]I received phone calls from growers this year,
[00:08:02.800]as well as from some agriculture magazines about this
[00:08:07.377]and that is true before sometime US Court of Ninth Circuit
[00:08:14.160]has canceled the registration
[00:08:16.500]of three dicamba based herbicides
[00:08:19.470]that include XtendiMax, Texapon and Enginea
[00:08:23.760]and it is possible that those herbicides
[00:08:27.430]may not be available in the marketplace next year
[00:08:30.750]because the registration of those three products
[00:08:33.340]is expiring by the end of this year.
[00:08:35.720]And in fact, because of this court ruling, U.S. EPA,
[00:08:42.980]made a notification that those products
[00:08:45.280]can be used only up to July 31st this year
[00:08:49.860]or you have to apply within 45 days of planting,
[00:08:53.590]whichever comes first.
[00:08:55.390]So basically after July 31st,
[00:09:00.420]growers will not able to apply those three
[00:09:03.570]dicamba base products, XtendiMax, Texapon and Engenia.
[00:09:09.870]And so if those products are not available
[00:09:11.960]in the marketplace next year,
[00:09:13.540]then particularly in soybean,
[00:09:15.650]our control options will be
[00:09:19.590]just using glyphosate based herbicides
[00:09:24.550]for postemergence weed control,
[00:09:26.320]and they may not work very well
[00:09:27.940]because we have at least six weeds in Nebraska
[00:09:31.680]are resistant to glyphosate
[00:09:33.410]and that include Waterhemp, Palmer amaranth,
[00:09:36.240]kochia, marestail, common ragweed and giant ragweeds.
[00:09:40.790]So these six weeds have evolved resistance to glyphosate
[00:09:44.440]and some of them are widespread, particularly waterhemp,
[00:09:48.507]marestail, and Palmer amaranth,
[00:09:50.820]they are very widespread and you will see in several fields.
[00:09:54.730]So depending only on glyphosate
[00:09:57.290]will not help to control them.
[00:10:00.570]So in that case,
[00:10:01.800]particularly for postemergence herbicides,
[00:10:03.960]you may need to use some PPO inhibiting herbicides
[00:10:07.800]that are available in the marketplace
[00:10:09.690]for example, Cobra, Ultra Blazer, Reflex, Flexstar,
[00:10:14.660]all those are great examples of PPO inhibiting herbicides.
[00:10:19.890]Another alternate will be if you plant LibertyLink soybeans,
[00:10:23.520]then you can use a glufosinate based herbicide,
[00:10:26.500]such as Liberty or Interline or Cheetah.
[00:10:30.310]Those are some examples of glufosinate based herbicides
[00:10:34.630]available in the marketplace.
[00:10:35.790]But you can only apply when you plant LibertyLink soybean,
[00:10:40.180]you cannot use Liberty or glufosinate based herbicides
[00:10:44.700]in dicamba resistant soybean
[00:10:49.060]Great-
[00:10:50.140]So the best way next year will be,
[00:10:52.800]do not rely only on postemergence herbicides
[00:10:55.650]and you have to start with a good preemergence herbicides,
[00:10:59.790]which should be a good pre-mix of two or three herbicides
[00:11:04.130]that will be a good start
[00:11:05.300]and then they can come back,
[00:11:07.830]when weeds are less than five inch tall
[00:11:09.730]they can use any of the aforementioned herbicides.
[00:11:13.560]So that will be the good plan to start with
[00:11:16.480]because in soybean,
[00:11:17.440]we have really good, preemergence herbicides to start with.
[00:11:23.500]So you're saying next year,
[00:11:25.030]you may wanna rely more or pay more attention
[00:11:27.610]to what you're putting down on you pre,
[00:11:29.030]'cause that's- Preemergence.
[00:11:30.090]More important especially if those three dicamba products
[00:11:32.630]aren't available for use in soybeans.
[00:11:34.550]Absolutely yeah, that would be my best recommendation
[00:11:37.120]is to start with a good preemergence herbicide
[00:11:40.230]and make a foundation for good weed control.
[00:11:43.700]All right.
[00:11:47.600]Just kind of a reminder,
[00:11:49.290]even though soybean based dicamba
[00:11:51.640]or dicamba soybean products aren't gonna be available
[00:11:55.450]that doesn't mean that there won't be risk
[00:11:57.130]for dicamba drift through the season
[00:11:59.340]because dicamba is used for other crops.
[00:12:03.660]Yes, dicamba based herbicides
[00:12:05.497]are being applied in corn and also in sorghum.
[00:12:10.750]So yeah, risk is there
[00:12:12.630]for off target dicamba injuries issues.
[00:12:15.210]And that's why I always recommend to use
[00:12:20.890]dicamba based herbicides without adding ammonium sulfate.
[00:12:25.010]Even if you apply in corn,
[00:12:27.540]for example, in corn,
[00:12:28.530]there are a number of dicamba based herbicides
[00:12:30.610]are labeled for example,
[00:12:32.390]clarity status DiFlexx, DiFlexx Duo
[00:12:35.820]all those are great examples of dicamba based herbicides
[00:12:38.840]being applied in corn.
[00:12:41.420]So I recommend growers not to add ammonium sulfate
[00:12:45.030]because for example, this year we had several days,
[00:12:47.740]it was windy and temperature was more than 90 degrees,
[00:12:51.740]almost every single day in last month or so.
[00:12:55.250]And so when you apply dicamba based herbicides
[00:12:57.530]when temperature is very high and it is windy then...
[00:13:01.300]and also with ammonium sulfate
[00:13:03.040]then it increases chances of
[00:13:05.210]off target dicamba injuries issues, it could be volatility.
[00:13:10.530]And so I recommend even if it is a dicamba based herbicides,
[00:13:14.970]applied in corn or sorghum, do not add ammonium sulfate.
[00:13:20.620]And I know this is a little out of your wheelhouse
[00:13:23.220]cause you work with crops,
[00:13:24.620]but it's also a nice reminder to let people know that
[00:13:27.400]dicamba is in a lot of over the counter
[00:13:31.350]readily available lawn care products.
[00:13:35.540]So, pay attention to...
[00:13:37.470]If you're starting to see injury in your gardens,
[00:13:40.010]pay attention to what you're spraying
[00:13:44.054]and especially don't apply dicamba
[00:13:46.250]when the temperatures are gonna be getting over 80 degrees
[00:13:48.730]onto your lawn,
[00:13:49.563]'cause that's gonna have adverse effects
[00:13:51.330]to other stuff in your growing area.
[00:13:55.090]Absolutely, yeah.
[00:13:55.923]That's a good point.
[00:13:57.800]Number of dicamba based herbicides are labeled
[00:14:00.650]and being applied for broadleaf weed control
[00:14:03.370]in non-crop areas as well as in lawns
[00:14:06.910]and some other structures.
[00:14:09.540]So it is important to keep all the best management practices
[00:14:14.700]so we can get best out of dicamba based herbicides applied.
[00:14:21.360]So earlier you mentioned your trials.
[00:14:23.665]Unfortunately due to current events,
[00:14:25.810]you were not able to have your weed field days
[00:14:28.950]that you would normally have.
[00:14:30.820]Do you have any programming available
[00:14:33.470]to take the place of those?
[00:14:37.090]Recently we video recorded all the projects
[00:14:39.830]that we generally include
[00:14:41.850]for the in person weed management field days,
[00:14:45.120]as well as resistant weed management field days.
[00:14:48.860]So this year we video recorded all of them
[00:14:51.080]and we were not able to conduct in person field days,
[00:14:54.410]and they are now available online.
[00:14:57.210]If you go on CropWatch website, or even on our webpage,
[00:15:03.010]you will able to see, we have video recorded
[00:15:04.910]all the projects with my graduate students,
[00:15:07.270]and it is available to see free of cost
[00:15:12.420]and those are great information.
[00:15:15.830]So one field day we virtually recorded
[00:15:20.810]at South central Ag Lab,
[00:15:22.550]that includes number of projects
[00:15:24.360]for weed control in corn, soybean, popcorn.
[00:15:28.040]And another virtual field day's available
[00:15:31.420]that was conducted at growers field near Carlton.
[00:15:35.960]This grower's field has, Palmer amaranth
[00:15:39.260]which is resistant to atrazine glyphosate
[00:15:42.270]as well as ALS inhibiting herbicide.
[00:15:44.930]So management of this Palmer amaranth
[00:15:47.850]is challenging in corn.
[00:15:50.100]So we have conducted a number of studies in growers field,
[00:15:54.820]and those are also available online.
[00:15:57.640]We have really great projects, for example,
[00:16:01.540]how row spacing and herbicide programs
[00:16:05.030]can best control this resistant Palmer amaranth
[00:16:09.520]in field corn.
[00:16:11.000]We also have a project where we are evaluating
[00:16:14.560]number of early postemergence
[00:16:16.420]or late postemergence herbicides,
[00:16:18.270]for effectively controlling Palmer Amaranth,
[00:16:20.920]which is not very ideal.
[00:16:22.230]We always recommend to apply preemergence herbicides,
[00:16:25.520]particularly for management of Palmer amaranth,
[00:16:27.930]because it can emerge throughout the growing season.
[00:16:31.110]So you have to start with preemergence herbicides,
[00:16:33.400]but sometimes for example, last year,
[00:16:36.160]when growers planted their crops
[00:16:38.300]and it was raining continuously,
[00:16:40.360]so they were not able to go in the field
[00:16:42.300]and by the time weather was cooperative,
[00:16:44.920]crops already emerged.
[00:16:46.400]So sometimes it happens
[00:16:47.790]when you do not have a chance
[00:16:50.060]to apply preemergence herbicides
[00:16:51.800]and then the postemergence herbicides,
[00:16:53.800]are only options for you.
[00:16:55.180]So under this condition,
[00:16:56.910]under worst case scenario basis,
[00:16:58.510]we have evaluated some early postemergence
[00:17:01.140]or late postemergence herbicides
[00:17:03.110]for controlling Palmer amaranth in field corn.
[00:17:06.800]As well as we also have a project about controlling and
[00:17:10.450]comparing preemergence herbicides
[00:17:12.330]labeled in non-GMO white corn,
[00:17:16.040]because postemergence herbicides are very limited
[00:17:19.110]because you cannot use glyphosate
[00:17:21.150]or glufosinate based herbicides in non-GMO white corn.
[00:17:25.330]And we have several non-GMO white corn growers,
[00:17:28.560]particularly in South Central Nebraska,
[00:17:31.510]they are directly contract farming
[00:17:33.700]and they can get better crop price
[00:17:36.530]if you compare with field corn.
[00:17:39.220]So we also have a project for them,
[00:17:41.910]which preemergence herbicides they can consider
[00:17:45.150]for applying in non-GMO white corn.
[00:17:48.140]So we have some interesting projects
[00:17:49.720]and they're all available online.
[00:17:52.330]All right, and just to remind people,
[00:17:53.720]those products are available on the CropWatch website
[00:17:56.440]and on Amit's research website.
[00:18:00.090]Yes.
[00:18:01.050]All right.
[00:18:01.883]Well, thank you for joining us today Amit,
[00:18:03.620]I appreciate it.
[00:18:04.520]Hopefully we have a good growing season.
[00:18:06.700]Sure Thank you, Mike.
[00:18:07.880]Have a nice day.
[00:18:08.713]You too.
[00:18:09.791](upbeat music)

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Drought's Impact on Weed Control

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