Hi I'm Daniel Smith, Southwest Regional agronomist for the Nutrient Pest
Management Program in the University Wisconsin-Madison and Extension. Today
I'm going to talk to you about herbicides and cover crops. First thing
to keep in mind is what is a cover crop versus a forage crop. A cover crops when
no biomass is harvested and uses the plant of your soil conservation purposes.
A forage crop is where we're watching the harvest that biomass through either
grazing or mechanical harvest. The cover crops can certainly be utilized as
forage but there's a few things that we should think about before we plant them
to ensure success. Most pesticide labels may or may not have cover crop data but
they usually have forage crop data that we should reference for rotational
restrictions, and we should plan our pesticide applications and cover
cropping around these rotation restrictions if we intend to harvest
these for feed. So we look at an example look at several herbicide labels where
we're looking at winter rye and looking at these rotational restrictions. A
rotational restriction on a herbicide label tells us how long we have to wait
between herbicide application and when we can plant a crop that's going to be
harvested, that potentially may have some negative impacts from these herbicides
being applied, and thus we want to limit the exposure that food crop to those
herbicide residues. For herbicide A here we look at the herbicide label and
says do not rotate to food or feed crops other than those listed below for all
other crops not listed wait at least 12 months following the last application.
Barley, oats, rye, and wheat, may be planted four and a half months following
treatment. We look at herbicide B and it has similar language except for the
rotational use for this herbicide is 11 to 18 months depending on the herbicide
rate. This is something we should be thinking about when we're planning our
herbicide applications this year is, well am I gonna plant a cover crop in the
fall that I'm then gonna want to graze or harvest for forage value the next
spring, if so I needed to examine that rotational restriction to make sure that
I'm not gonna have a problem when it comes to next spring when I want to
harvest it and there may still be a herbicide rotational restriction on that
field. We look at another example in this particular herbicide has cover crops
right on the label. And the language is fairly clear and it says cover crops are
not grazed by livestock nor harvested for food. And these cover crops are
planted for mostly soil and ecology based reasons out in the field. We looked
at using these herbicides and then planting a cover crop and it says on the
label that significant injury may occur if we're not following these full
setback periods. Often on these labels AHS included some language about doing a
field or a small-scale bio assay. That way we're testing for these residuals
and seeing if cover crop seed will germinate and survive any potential
residue that's out in the field, thus saving us from seeding in an entire field
and having a failure, or having an issue down the road where we really can't
harvest this biomass from this field because we do have a rotational
restrictions still in place. We look at an example through pictures to better
illustrate this we have herbicide A here on the top and herbicide B. We're
applying both these herbicides on May 1st and you can see I'm planting green
into a cover crop. Four and a half months go by and it's
September 15th and it's time to harvest our silage corn so we have our field
of silage corn harvested and I want to plant some winter rye out there for a
cover crop. I want to hold the soil in place,
maybe I'll go ahead and raise that cover crop but I should look at my herbicide
label and just see if I can legally do that or not. When I look at my herbicide
label herbicideA is gonna allow me to do it because there's been four and a
half months, herbicide B however though has an 11 month rotational restriction.
So it'd be illegal to plant my forage crop on April 1st the following year and
I'd have no rotational restriction. I could still go ahead and plant my
cover crop I just not have any forage harvest as an option, and any herbicide carryover
from that herbicide onto that cover crop would be the responsibility of the
producer and clearly if we had some herbicide carryover that may injure the
cover crop that may reduce the stand and may result in the stand failure. So
that's a pretty significant risk but as far as being able to plant a forest crop
we've got to wake those 11 months. And then clearly the next spring herbicide A
after four and a half months in planting that cover crop,
we could harvest that for forage, however then the other application, herbicide B,
we'd have to just terminate that cover crop and we could plant into it - still
have great weed suppression benefits if it still have some soil conservation
benefits obviously but we would not be able to use that for forage. We look at
herbicide persistence and carryover, this is when we see reduced stands of cover
crops out in the field, and they may not be noticeable when we drive by in the
pickup truck and look at that field, we may not see a decrease stand of cover
crops. Well when we go out and scout, we may find areas of field, we might find a
whole field that has less cover crop than a neighboring field that we plant
in the same day. That's when we start to think about, gosh maybe there's some
herbicide carryover issues going on out here. So we have two pictures here of a
radish planting we have a non treated plot, nice stand of radish, and then we
have some herbicide carryover, a severe stand reduction of the radish, you can
see some injury occurred on that radish. So how does this happen? This happens
when we apply a residual herbicide, and it sticks around for a little bit longer
than intended. Sometimes it doesn't stick around for longer than intended, it's just
that length of the residual is that long that we have enough herbicide out
and so that's gonna negatively impact a cover crop, and in that particular
instance that would be maybe an interceding pass, where there's only 20
or 30 days between application and establishment, and this is where looking
at our herbicide labels and doing some label researches very important if we're
gonna use cover crops and residual herbicides in our crop rotation. We look
at the properties that influenced herbicide carryover and persistence, we
think about the chemical properties of the herbicide, more particularly the
half-life of the herbicide, the rate of the herbicide application, the soil pH
- heavy soils and high pH equals longer residual that herbicide - the
organic matter content of the soil, the amount of surface plant residue
and tillage - so the tillage is going to dilute through these residues - we think
about temperature and rainfall - less rainfall equals longer residual of these
herbicides in most cases - and then the microbes in the soil and how they're
going to break down this herbicide. So we look at a example from the farm
landscape of herbicide carryover, this field is in southern Wisconsin, and we dig
into scouting this nice stand of cover crops, a little bit
closer we find that something's missing or stunted. So look at this photo on the
tailgate and we see that there's a nice healthy stand of peas that we dug up
from along the edge of the field, but when we move into the field farther we
get this stunted plant and we see a lot of the pea population had actually been
reduced throughout that field. We start to look at that pea plant a little
bit closer, and we see some stunting, we see the nodes are a little bit
closer together, we see some clear herbicide injury.
This was from a herbicide that was applied about three months prior to
cover crop establishment, had some rotational restrictions on it, and then
our weather conditions were favorable for some herbicide carryover
to take place. Looking at a few more examples of this, and we look at
some research that was done several years ago at the University of Wisconsin-Madison's
Agricultural and Life Sciences research station in Arlington
and we see in our non-treated plots we have this nice healthy stand of
annual rye grass with about sixty-six percent cover is the number in the white
box. So this green cover about sixty-six percent of the soil is covered with this
cover crop we start to compare that to other herbicide treatments we can see
that's decreased significantly, depending on what herbicide is used, so
we're seeing some herbicide carryover in these plots. Moving on, we can think about
what to you in the spring with our cover crops, and we can think about our cover
crops becoming spring weeds if they're not managed properly, so our first slide
here shows a photo of a nice healthy stand of winter rye, you know rye grass,
clearly a very healthy cover crop providing some great benefits, and we
look at the slide on the right is a nicely terminated cover crop that we can
plant back into. So we often get this question: "Well, is it possible to have
herbicide resistant cover crops?" and we look at some of the herbicide resistant
cases from across the world, we find out that Italian rye grass, better known as at
annual rye grass, shows resistance to five herbicide site of action groups in 14
states in the US and some countries across the world. So when we think about
this, this is also where some of our annual rye grass seed is produced, so we
should be cautious when using any rye grass and always have a really good
termination plan for annual rye grass to prevent it from going to seed. Oftentimes,
when we're terminating annual rye grass, it's two to three weeks before it even thinks
about producing seed, so we shouldn't have a huge extreme issue of an escape
of annual rye grass, but it's something to keep in mind in a
management plan. We think about seed production and a little bit more in
depth we think about how quickly these cover crops can flower and produce seed
in the spring. In certain cover crops can over winter from these seeds, such as rye,
buckwheat, and hairy vetch, they all over winter and then they produce seed
the next year. This first photo here is my hand and that's buckwheat seed and
that's about 60 days after buckwheat was planted in a research trial at the
Lancaster Agricultural Research Station. Moving on to the next photo, that's
winter rye and it's near mid-june and it's starting to think about producing
viable seed, as well. As is the the next slide on the back of a tailgate is
annual rye grass, so that's producing viable seed near the end of May.
Finally, the last photo is from that southern Wisconsin field again and this
is one that we often don't see go to seed in Wisconsin, that's radish. Radish
actually produced seed in this particular field and could become a weed if we
didn't think about it for the next growing season. We think about our cover
crops that over winter versus the ones that winter kill and we find some
variability in annual rye grass, so we did some field studies that were in 2013-
2014 three out of our four varieties survive the winter. However, in 2014-2015
all of our annual rye grass winter killed.
We look at the chart on the right hand of the screen and we see some our most
common cover crops starred. We see annual rye grass may overwinter, oats is
always going to winter kill, winter rye is always going
to over winter, radish will always winter kill, crimson clover may or may not
winter kill, depends on where you're at in the state of Wisconsin and depends on
what kind of winter we've had, and then red clover will typically always
over winter. We'll terminate these cover crops once they've over wintered
Obviously, if we're planting some of these grass species that winter kill
we're gonna have a nice seed bed to plant back
into that mulch from the the terminated cover crop via winter kill, but if we need
to do some termination with some of our other tools. Crimping can be a
great tool to have in the toolbox, especially with winter rye, to crimp the
winter rye and plant soybeans back into has been shown in Wisconsin to produce a
great soybean yield and provide great weed control. We think about mowing
some of our cover crops, so you can get away with mowing some of our grass species, however
be mindful that some of these cover crops will quickly regrow, such as annual
rye grass will regrow very similarly to the grass in your lawn. Winter rye, if we
mow it towards the end of the vegetative and into the reproductive stages of life,
we can expect very little regrowth to occur and we can be fine with planning
just a second herbicide pass to clean up weeds in any escape dry plants that
survived through that mowing pass. We can think about doing some tillage,
however I'm not gonna recommend tillage passes unless we need to for our crop
rotation or a cropping system, because tillage is gonna really undo some of
those benefits of the cover crop that we've seen such as reducing soil erosion,
building soil health, and that type of thing. Finally, we have
herbicides in the toolbox, we can think about using glyphosate burn down pass,
but we want to have good weather conditions a termination timing. Brassica
termination we're not gonna really have to think about terminating these
brassicas in Wisconsin, because they're gonna winter kill. The two photos show
two extremes, we have one picture here that shows the the interceded
radish, the brassica species that is really not going to produce a whole lot of
biomass in the fall, and it really is not gonna provide a lot of cover crop
benefit so we should think about maybe the timing of when we planted that to
improve the benefits, but again that green biomass we've seen in the fall
isn't gonna be there in the spring. We look at the photo on the right again, we
can think if we planted monoculture brassicas, we're gonna have a field that
the soil has been loosened and is very prone to erosion, so we should think
about planting these species with a grass cover crop that again is going to
need to be terminated in the spring. Finally, the legumes are going to require
some termination depending on what species you plant. Again, we covered a
few of the common ones are gonna winter kill, like
crimson clover, peas, but red clover and vetch they're gonna need to have a
termination pass down in the spring. A few of these are good candidates for
crimping, you can see that on the slide. Mowing may be an option for a couple of
these if we're going to terminate them in the same year that they're planted,
but the species that over winter are not going to be species where we mow. And then
tillage, of course, is always an option in the toolbox, but again I'm going to
advise against it unless we absolutely have to for a cropping rotation. We think
about terminating the legumes, I'm gonna recommend a application of a glyphosate
product coupled with a growth regulator herbicide. These will provide
adequate control of these cover crops and any weed species that are out in
that field hiding out underneath that cover crop residue. We think about work
to do if we're gonna do a forage harvest of some of these cover crops, so we have
winter rye and annual rye grass, we're gonna harvest these species around boot-
stage for the winter rye and what's that gonna look like if we allow those to
regrow? So the very front of this photo shows winter rye two weeks after harvest
and we do get a little bit of regrowth, but you know we're talking about five to
six inches of regrowth, we can easily plant into that and clean that up with a
post emergent application. Annual rye grass however, though, quickly regrow produced
quite a bit of biomass, but after harvest and that would be a clear weed and
provides some pretty strong competition to whatever crop we planted back into
that. We think about harvesting that winter rye or annual rye grass for forage value and
then spraying it the same day. So this research showed that we could go out, we
could harvest our winter rye and annual rye grass,
take that biomass off the plot, store it for feed value, and then we can go ahead and
spray it the very same day and we could have excellent control after two weeks
with just a burn down application of glyphosate. Then finally, we look at
glyphosate alone on these cover crops on this particular instance, we're leaving
that cover crop residue on the soil, we want to go out and we want to
spray those cover crops off, we could go out and plant into that
residue. I also want to encourage producers to explore their options when
it comes to managing this cover crop residue, by ensuring that they have
proper planter setups to plant into that residue, and consider modifying
their equipment for optimum success in these high residue systems.
Cover crops and crop insurance: we want to always ask our our crop insurance
agent and check our policies to avoid future problems with our crop insurance,
and cover crop termination can be quite simple for crop insurance reasons,
however there are some reasons why we should investigate a little bit
further and talk to our agent to ensure that there's no problems down the road.
I also want to encourage producers to terminate their cover crops under good
weather conditions, so when the cover crops actively growing, when the daytime
temperatures are above 50 degrees, and the nighttime temperatures are above 40 degrees,
when that cover crop is actively growing and ensure that
the sprayer is set up for an optimum application for serious success, if we're
going to use a herbicide to terminate your cover crop. With that, I'd welcome any
questions and emails at the phone and email address on the screen, as well as
reaching out to your local Extension educator for more information.