Hi i'm Daniel Smith, southwest regional
agronomist from the Nutrient and Pest Management
Programr at the University of
Wisconsin-Madison campus. Today I'm going
to be talking about practical weed
management for low-margin years. It's
important to manage weeds, regardless of
crop prices, to protect crop yield and
not increase the soil seed bank. Since
glyphosate tolerant crops were introduced
weed control practices have changed and
become more relaxed. Older chemistry
however offers great opportunities for
low-cost options. However some problems
with these older chemistries may exist,
such as herbicide injury in agontonistist
effects that may be occurring on the
field. We should always know our weeds
and field histories. We should evaluate
keep detailed records of these practices
and use crop rotation. You should have a
plan to prevent herbicide resistance and
this includes using post and pre-emergent
herbicides at the label rates. Multiple
modes of action should be contained in
these herbicide applications. We should
scale prior to herbicide applications
and then two weeks following herbicide
applications, we should scout again to
identify any misses or potential
herbicide-resistant concerns. Generic
herbicides may help reduce costs, and only
using the necessary adjuvents would
also help improve the bottom line.
Preseason planning is very important in
management! Understanding the weed
biology out in the field is important to
develop a diversified approach towards
weed management and focusing on the weed
seed production and reducing the number
of weed seeds throughout the soil seed
bank. Using cultural, biological, and
chemical control methods are all
necessary. Selective herbicides from multiple
motive action is key. We should know our weeds
and field history. The photo shows Palmer
amaranth and waterhemp on the
field. This seed is maturing but not
mature yet, so we should have a plan to
limit
seed production out in the field. This
could include mowing those seeds off. At this
point, yield loss will be critical out
in that field and it's important to manage
this field so we don't increase the seeds
that are out in the
soil seed bank. The second photo shows
mature giant ragweed out in a cornfield
where the seed is already viable. So at this
point, we may go to salvage a little bit of
yield out the field, but we want to limit
seeds from moving around out in the field.
We want to manage this field to prevent
future giant ragweed problems. The next
slide shows the spread of herbicide
resistance out in the field. The first
photo shows a small patch of weeds that
turned out to be glyphosate-resistant
that were allowed to mature and
produce seeds and then that field was
combined. In year 2 those seeds emerged
all the way through the field, since
they were spread through the combine and again
targeted with glyphosate. I allowed those
weeds to survive and produce seeds for a
second time. The field was combined again at the end of
year two and at the end of
year three, we had a widespread weed resistance
concern. And we'll have future
management issues to try and manage that
soil seed bank. And these photos are courtesy
of the Ohio State University. In season
agronomic practices make a huge
difference on how our weed management plan
is implemented. We should plant into weed-
free fields and keep fields as weed-free
as possible. We should always be planting
crops seed that is weed free and scouting
regularly. Using multiple modes of action
that're effective against the most
troublesome weed species out in the
field or those are most prone to be
resistant is critical and applying the
recommended rates for these weed
species based on weed size. We should
emphasize cultural practices out in
the field such as crop rotation and
using mechanical and biological methods
are appropriate to control weeds. In the
harvest and post-harvest timing, we
should avoid weed seed movement by cleaning
equipment, investing in a little bit of
time to make sure our equipment is free of
weed seeds from moving field to field is
critical.
Harvest fields with resistant concerns
or widespread weed issues last. In
preventing field to field and within
field movement of weed seed is critical.
Managing weed seed at harvest and after
harvest prevents the soil seed bank from
building up and managing field borders
can
prevent weeds from moving into the field.
The future costs of poor weed
management include hand weeding, failed
herbicide attempts, tillage, yield loss, and
increased costs to reduce that soil seed
bank. And these can be done in several ways.
Hand weeding has been utilized in some
southern states with a typical cost of
$75 per acre. Using herbicide multiple
times and not realizing herbicide
resistance is occuring, costs farmers
time and money. Often yield is lost to
patches and even complete fields due to
the lack of management. Technology
developed to prevent the spread of
weed seeds is present and has
been developed by an Australian farmer.
The seed to structure costs anywhere from
thirty thousand to a hundred and eighty thousand
dollars for the unit loan. And this
machine turns the weed seed into a
flour and shaft-like material to prevent
the weed seed bank from building. This is
the herbicide mode of action chart. And
once a herbicide is purchased, it's hard
to change the mode of action,
obviously. So it's important to make a
plan to control the weeds on your farm
first. So we should identify the weed
species that historically has been
problematic and second consider the
herbicide resistance species either on
our farm are currently in the area. We
should plan to prevent herbicide
resistance by selecting a herbicide that has
multiple modes of action either as a
premix or mixing multiple products
together. Always read and follow the
herbicide label and herbicide resistance
can occur from selecting the same
herbicide over time creating species that
may be less susceptible to control.
Herbicide resistance in Wisconsin
was first seen in 1979 with common
lambsquarters resistance to PS2
chemistry, through the over-reliance of
atrazine. Through the 1990s we saw ALS
and then finally glyphosate resistance
concerns in Wisconsin. The following few
slides will show us county by county
where herbicide resistence is a concern.
The first side details Horseweed.
Velvetleaf, Common Ragweed, Giant Ragweed,
Waterhemp, which is widespread
in Wisconsin with quite a few cases
of confirmed glyphosate resistance in one
county that has glyphosate and PPO
confirmed resistance and finally Polymer
Amaranth, which is confirmed to be
resistant in two counties in
glyphosate and has HPPD and ALS
inhibitor resistance in another.
It's important to scout prior to herbicide
applications to identify the weeds
present and to measure the weed size and
stage the crop.
It's important to know how big our weeds
are so we can target the correct herbicide
chemistry towards these weeds and
knowing the crop size allows us to make
a legal herbicide application because
there are restrictions on crop size on
herbicide labels. Using a preemergence
herbicide can help us prevent weeds
from emerging and use this product at a full
labeled rate so we don't have any weed
escapes. Follow the label for recommended
application method spray volumes and
additives for the most success. Adding a
burndown herbicide may be necessary if we have
a lot of weed species already on the
field and choose our preemergenence
herbicide based on our field histories.
This is a sample plan for management of
Waterhemp and Palmer Amaranth in Wisconsin
in soybeans. And there are many good
herbicide choices in Wisconsin and
we should always be looking for university data
on weed control to make our final
selection of a herbicide. We should select
our herbicides based on availability, efficacy, and
cost. Our sample preemergent herbicide may
include a burndown if we need to kill
the weeds already out in the field or a
tillage pass can be done. So for this
instance in soybeans, were going to
apply a PRE of S-metoachlor and Metribuzin
for two sites of action of 15 and 5. And
then we're going to follow up with a post
application when the weeds are four
inches or less of fomesafen and glyphosate
for fourteen and nine site of
action groups or lactofen and glyphosate
for those same site of action groups for
a total of four different modes of
action applied to this field. Generic
herbicides may help reduce costs. Glyphosate
is a great example of a product where many
generic herbicides exist. So in this
example, we want to use glyphosate as a
spring burndown application and we
want to apply 1.125 pounds acid
equivalent glyphosate per acre. Product A
is a brand named glyphosate product and
we can apply that at 32 fluid ounces per
acre per the label. And this cost is seven
dollars and fifty cents. Product B is a
generic glyphosate and calls for 36
fluid ounce application rate for a cost of four
dollars and seventy-eight cents. The
application rate difference is due to a
different acid equivalent per gallon of glyphosate
formulation so it's important to
read and understand the entire label of the
herbicide. For this particular example
we're going to save two dollars and 72
cents per acre and on a 500-acre farm
that would be equivalent to $1360
savings. Adjuvants are necessary
in some circumstances for the best
herbicide performance. We should always
read the herbicide label and this will
indicate what herbicide adjuvants are
necessary. And then we should also read
the additive label to look for the
active ingredients. We should always be
researching the products that we're
purchasing and we're not going to be
able to fall for snake oil solutions if
we do all the proper research on these
products. Using the postemergence
weed control practices based on the weed
species present and field histories is
critical. The University of Wisconsin
publishes publication number A3646 pest
management in Wisconsin field crops is a
great guide to learn more information
about herbicide controls Table 2/3E
details postemergence herbicides for
corn and there's many of these charts in
this book. We'll look at the very first product, 24D
with a motive action group 4 and a
risked corn injury of 4. 24D will not have
any controlled grasses, so we move on to
broad leaves and that gives you control rating.
These ratings are from 0 to 10, with 0 being
the worst control and 10 being the best.
If we look, there's several weed species listed here.
For example, lambsquarters has a
rating of nine, so that would provide
fairly decent control to lambsquarters
out in the field. We should always be
looking also for our perennial species to
see if there's going to be any control in
these based on
herbicides. It's important to know our
weed life-history out in the field and
there's five key pieces to weed life
history. The first being, when the
plants emerge,
what is the optimal growth stage for
control and how much seed does one
plant produce? How far does the seed travel
and how long does the seed persist in the soil?
So we're going to look at Common Waterhemp for
the first example. It emerges in that
mid-may time period and can emerge
all the way through August. It will
produce 250,000 seeds and has a weed
seed persistance of 4 years or less. If we jump
down to common lambsquarters, that will
emerge a little bit earlier than Waterhemp
in that mid-April time and all the
way through August. We move over to what's
being produced, about 72,500 seeds. However,
those seeds can persist for about 20
years. Finally, if we look at giant foxtail
the weeds will emerge in a mid-may time
all the way through August, produce
about 1,500 seeds and persist for 20
years or more. It's important to evaluate and keep
detailed records of our weed control
practices. This includes photos of our
weeds out in the field. This first
photo shows some mature giant ragweed
seed and I could save that photo with my
scouting report when I get done.
It's also important to keep detailed
records of pesticide applications and
use those records once you're out there
scouting past the herbicide application
to see if we had a good match with a
herbicide selection to the weed species
that we targeted in notes any misses that
we had out in the field. Small costs
now are going to equal future savings. We want
to spend a little bit of money now to
prevent those costly options of managing
either herbicide weed resistance or weed
escapes. We should know our weeds and
our field histories to evaluate and keep
detailed records of these weed control
practices and always use crop rotation.
We should have a plan to prevent
herbicide resistance to save money in
the future and this plan should be based
on field history and weed population. Using
a pre-emergence and a postemergence
herbicide at full label rates is critical
as is choosing multiple modes
of action. We should always be scouting
prior to herbicide applications to
selective the crops proper control
methods and then scout after the
herbicide application has occurred
several weeks passed to identify any
misses on the field.
Generic herbicides may be necessary to
reduce costs and only use necessary
adjuvants. With that, that concludes my
presentation on low margins and weed
control and I'd welcome any questions at
the following email and phone number.