Late-Maturing Crops and Insects

Michael Sindelar and Robert Wright Author

09/06/2019 Added

2 Plays

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In this CropWatch Podcast Michael is joined by Nebraska Extension Entomologist Robert Wright to discuss insect issues in late maturing corn and soybeans. Aphids, grasshoppers, rootworm beetles, and woolly bear caterpillars are the star pests of this podcast.

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[00:00:00.769](upbeat music)
[00:00:02.970]Welcome to CropWatch Podcast.
[00:00:05.410]A production of Nebraska Extension.
[00:00:12.830]Welcome to the CropWatch Podcast.
[00:00:14.960]I'm Michael Sindelar, cropping systems extension educator.
[00:00:17.990]For today's CropWatch Podcast,
[00:00:19.580]we'll be talking about late season
[00:00:21.030]pests in corn, specifically insects.
[00:00:24.140]I'll be joined today by Dr. Robert Wright,
[00:00:28.260]who is a specialist and professor
[00:00:30.930]at the University of Nebraska,
[00:00:33.520]so Dr. Wright, what are our targeted pests
[00:00:37.720]in the late season for corn?
[00:00:39.770]What are we looking for when we're
[00:00:41.070]out in the field scouting?
[00:00:43.450]Well historically or typically,
[00:00:45.120]the two issues we probably would see
[00:00:47.940]most commonly would be spider mites and grasshoppers.
[00:00:52.120]With the wet weather we've had
[00:00:53.590]in a lot of eastern Nebraska,
[00:00:56.110]I haven't heard a lot of reports on spider mites,
[00:00:58.480]although if it dries out in certain areas,
[00:01:00.770]that's always a potential to look for.
[00:01:04.600]I know we have grasshoppers in some areas,
[00:01:06.810]that's something to watch for as well.
[00:01:09.410]Particularly if the grassy borders
[00:01:11.273]start to dry down, or if you mow the grassy borders,
[00:01:14.930]that might drive grasshoppers into the crop.
[00:01:18.010]One thing we're seeing the last several
[00:01:20.100]years that we haven't seen as much in the past
[00:01:23.840]is we're seeing late season aphid populations in corn,
[00:01:28.270]post tasseling, I just got a call yesterday
[00:01:32.260]about that as well, so I know we're
[00:01:34.304]seeing that in eastern Nebraska more
[00:01:36.640]than we have in the past, so that's
[00:01:38.880]something else to watch for.
[00:01:41.100]So when you're dealing with the late season aphids,
[00:01:43.640]what are our control methods, or what are
[00:01:45.920]our best practices for working through them?
[00:01:49.370]Well, there hasn't been a lot of research
[00:01:52.060]in terms of potential economics for yield loss,
[00:01:55.310]so we don't have a good threshold.
[00:01:57.740]When I was visiting with somebody yesterday,
[00:02:00.940]some of the questions I was asking him was
[00:02:03.482]what stage is the corn, and are you seeing
[00:02:08.330]aphids in just spots, or was it pretty
[00:02:11.390]uniform across the field?
[00:02:12.830]Sometimes we have hotspots with the aphids,
[00:02:15.518]and it's only a few individual plants may
[00:02:18.810]be heavily infested but their neighbors aren't.
[00:02:21.720]In his case, he was saying the corn
[00:02:24.050]hadn't done it yet, and he had some fields
[00:02:26.320]that had heavy infestations that were pretty widespread,
[00:02:31.100]and in that case I suggest that you might
[00:02:33.170]wanna treat, and he was gonna treat, I think,
[00:02:36.510]in that case, so it has to be a judgment call.
[00:02:40.050]I guess the other question I didn't ask him
[00:02:42.530]but I assume we were talking about yellow
[00:02:45.170]dent corn if it's food grade corn
[00:02:47.240]or some other higher value corn,
[00:02:49.550]you might wanna pull the trigger earlier
[00:02:51.257]with higher value corns.
[00:02:54.292]So you definitely recommend scouting
[00:02:56.750]the field to understand how heavy
[00:02:58.640]the infestation is before you make
[00:03:00.420]a decision to treat or not to treat.
[00:03:03.740]Right, because in some cases,
[00:03:05.500]it's just a scattered infestation,
[00:03:08.080]but they can be individual plants
[00:03:10.560]that are very heavily infested,
[00:03:12.050]but their neighboring plants aren't infested,
[00:03:15.410]versus a case where there's a widespread infestation
[00:03:18.960]that's more or less across a field.
[00:03:21.330]Obviously, you're not gonna spot spray
[00:03:23.060]or just spray a field corner,
[00:03:26.060]so before making a decision to treat the whole field,
[00:03:30.710]it's good to know where the aphids are in the field.
[00:03:34.330]So with grasshoppers, you said
[00:03:36.437]they may become an issue after mowing or dry down.
[00:03:40.330]What are we looking at to make decisions
[00:03:42.356]off of that for grasshoppers?
[00:03:46.050]We have articles in CropWatch
[00:03:48.830]that have some general guidelines
[00:03:50.660]in terms of the grasshopper numbers
[00:03:53.580]on field borders and within the field
[00:03:57.028]in terms of the number of grasshoppers
[00:03:59.092]per square foot might be an issue.
[00:04:02.920]I guess the other thing to watch for
[00:04:04.370]would be how much on corn, how much feeding they're doing,
[00:04:07.750]if they're heavily damaging leaves up to the ear leaf,
[00:04:11.733]or getting close to ear leaf,
[00:04:13.400]that certainly would be concerning.
[00:04:15.970]And again, whether where that is distributed in the field,
[00:04:20.520]if it's just on the field edges, extreme edges,
[00:04:23.610]it might not be worth spraying the whole field for that,
[00:04:25.590]but might be worth spraying the field border.
[00:04:29.300]If there are still grasshoppers in the field border,
[00:04:32.730]you could spray that area.
[00:04:35.720]So with the year we had, there were
[00:04:38.870]a lot of late planted corn fields,
[00:04:41.450]how does the late maturing corn
[00:04:45.400]affect these decisions, or how to go about
[00:04:48.700]to treat or control these pests late in the season?
[00:04:53.392]Well, the one issue is any of the adult stages
[00:04:57.000]of these insects will fly around,
[00:04:59.450]particularly grasshoppers and aphids,
[00:05:03.720]and they can be attracted to late maturing crops,
[00:05:06.972]and so they may move into late maturing corn,
[00:05:11.510]they're still green while the rest
[00:05:12.940]of the fields are turning brown.
[00:05:15.600]And so they can concentrate on the late maturing fields.
[00:05:18.240]The other thing we haven't talked about
[00:05:19.640]are rootworm beetles, and if you have late silking fields
[00:05:24.390]in an area and in other cornfields, brown silk,
[00:05:27.805]rootworm beetles will fly around locally
[00:05:30.420]and concentrate in the latest maturing corn
[00:05:34.150]and lay their eggs there, and that's something
[00:05:36.730]to be concerned about next year, if you
[00:05:38.360]plan to plant that field back into corn
[00:05:41.077]and it was late maturing and had a lot
[00:05:43.940]of rootworm beetles in the field,
[00:05:45.360]there may be a heavier population
[00:05:47.280]of rootworms next year than you would've
[00:05:49.027]had with the normal planting date.
[00:05:52.670]So it'd be safe to say that scouting
[00:05:55.530]late maturing corn, it would be a positive
[00:05:58.181]that it requires more scouting than
[00:06:01.730]your other crops that are maturing more normal.
[00:06:05.330]Right, and with the case of rootworms,
[00:06:08.180]that's what we would do in our research plots.
[00:06:10.160]We'd plant late maturing corn to try to
[00:06:12.700]concentrate the rootworm beetles and lay eggs in an area
[00:06:15.920]where we wanna do research next year,
[00:06:17.847]and we wanna have high populations.
[00:06:20.760]Most growers don't wanna have high populations,
[00:06:23.360]and that's something you need to watch for,
[00:06:26.095]and if you're gonna be planting that field
[00:06:29.520]back into corn, you definitely wanna
[00:06:31.650]have some control efforts planned,
[00:06:34.590]either Bt corn that's active against rootworms,
[00:06:38.935]possibly a planting time insecticide as well,
[00:06:42.270]if there were a lot of beetles in the field.
[00:06:44.510]So when these heavy infested fields
[00:06:47.390]that were possibly heavy infested fields
[00:06:49.613]for controlling them, what strategies
[00:06:53.070]do you farmers wanna use to try to
[00:06:55.120]reduce resistance or work through
[00:06:57.005]partial resistance for tolerance?
[00:07:00.190]Well, part of it is knowing what's
[00:07:02.600]going on in your area.
[00:07:04.217]Are your Bt corn hybrids working well in your fields?
[00:07:08.580]Have you had failures in the past?
[00:07:11.560]That might be an indication you
[00:07:12.830]have resistance in your area.
[00:07:15.050]We don't have resistance statewide,
[00:07:17.440]but there are pockets that have resistance.
[00:07:20.490]There are other areas where the rootworms
[00:07:22.890]are still susceptible to the Bt proteins,
[00:07:25.330]so we can't make a blanket recommendation statewide.
[00:07:30.310]There's also the other option.
[00:07:31.930]I know some people might not like it to rotate, right?
[00:07:35.670]Well they have the other option,
[00:07:37.230]is if you have several cornfields and some of 'em
[00:07:40.632]were planted late this year and you
[00:07:43.140]noticed a lot of rootworm beetles.
[00:07:45.320]If you are gonna rotate some, those would
[00:07:48.000]be the fields to target for rotation,
[00:07:50.080]is they're the most likely to have
[00:07:51.480]rootworm problems next year.
[00:07:53.800]We talked about corn, what are
[00:07:55.660]we looking for in late season pass for soybeans?
[00:07:59.640]Well, there are several, again,
[00:08:01.970]grasshoppers would be an issue potentially.
[00:08:05.896]There are several beetles that will feed
[00:08:08.993]in soybeans, bean leaf beetles,
[00:08:13.140]but also rootworm beetles may move into soybeans,
[00:08:17.550]both in pastures, in some cases
[00:08:20.233]we've seen either northern or western corn rootworms
[00:08:24.240]or southern corn rootworms in high
[00:08:26.900]numbers late in the season and in late
[00:08:29.730]maturing soybeans, because that's the only
[00:08:31.860]green thing left for them to feed on.
[00:08:34.530]So in that case, we have defoliation thresholds
[00:08:38.500]for soybeans if any insects, and the combination
[00:08:42.500]of the insects is causing 20% defoliation
[00:08:46.690]in reproductive state soybeans,
[00:08:48.543]that would be a treatable level.
[00:08:51.400]We also are seeing our light trap
[00:08:54.080]and clay center, there's a fair number
[00:08:56.220]of moths that are active, some wooly bear caterpillar
[00:08:59.560]moths are active right now and may
[00:09:01.950]be laying eggs in soybeans, and any of
[00:09:05.270]the moths that might lay eggs in soy beans,
[00:09:08.480]green clover worms, we've had fair numbers recently.
[00:09:12.520]They're gonna be more attracted
[00:09:13.930]to later maturing soybeans that are still green
[00:09:17.100]and possibly flowering than other soybeans
[00:09:21.080]where the leaves are starting to turn yellow.
[00:09:23.890]So particularly scout those fields for insect activity.
[00:09:29.390]Both corn and soybeans we can think of
[00:09:31.340]as being an insect magnet,
[00:09:33.120]if they're late maturing, they're gonna
[00:09:34.950]be very attracted to what other insects are around.
[00:09:38.900]So you'll definitely say one of
[00:09:40.200]your take home messages today is
[00:09:41.992]to scout late maturing fields,
[00:09:44.690]whether they're corn or soy beans
[00:09:46.620]to understand what may be coming next year to plan for that.
[00:09:51.139]Right, and then also be aware that,
[00:09:54.208]at least the adult stage of these insects
[00:09:56.760]can move around, and they will move from field to field.
[00:10:00.540]Particularly as the earlier planted crops
[00:10:03.390]are beginning to dry down or turn color
[00:10:05.874]and reach maturity, and they would prefer
[00:10:09.450]to feed on nice lush green crops,
[00:10:12.480]rather than crops that are turning yellow or turning brown.
[00:10:16.440]So with the unfortunate events
[00:10:19.220]that have happened across the state
[00:10:20.950]and hail damage moving in, how would
[00:10:24.000]you change your recommendations
[00:10:25.740]for fields that may have experienced hail damage?
[00:10:29.439]Well, we don't have a quantitative way
[00:10:31.700]to talk about that, but in general
[00:10:34.220]if the yield potential is reduced,
[00:10:37.385]it's gonna be less profitable to treat,
[00:10:41.340]you're gonna be able to save less yield
[00:10:43.382]by treating a hail damage crop,
[00:10:46.600]so it's gonna be less likely to
[00:10:50.010]benefit from an insecticide treatment because of that.
[00:10:54.130]The insects are not particularly,
[00:10:56.259]at least the pest insects are not particularly
[00:10:58.640]attracted to hail damaged crops,
[00:11:00.990]so there's no special issue there.
[00:11:02.810]Again, if they dry down or start dying off early,
[00:11:05.710]they would be less attractive than
[00:11:07.130]maybe fields that aren't hail damaged.
[00:11:09.870]Well, thank you for joining me today Dr. Wright.
[00:11:12.560]Hopefully you have a good growing season.
[00:11:15.887]Thank you, you too.
[00:11:18.206](upbeat music)

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Late-Maturing Crops and Insects

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