Are you fearful, intrigued, confused,
or simply curious about herbicides? If so, you’re in the right place! Let’s dig
a little deeper into the science of how herbicides function.
To start off with, what is a herbicide?
A herbicide is a chemical that can manage and control
unwanted plant vegetation. The most common types of herbicides are synthetic,
but there are also organic options. These chemicals are typically used to
effectively eliminate weeds in order to maximize the growth of more desirable
plants. Herbicides can be utilized anywhere from your favourite golf course to
a neighbour’s garden, and everywhere in-between! It’s important to understand
the different ways these chemicals are applied as well as how they
physiologically affect plants.
Categories
of Herbicides
The two largest categories of herbicides
are selective and non-selective. Non-selective herbicides are designed to harm
just about any plant species that comes into contact with it. Selective
herbicides are formulated to target specific plants and leave others
unaffected.
Herbicides can be further classified by
their method of application. Some are formulated to be absorbed through leaf
and green material, and are spread in a foliar application. These are commonly
called “post-emergent herbicides.“ Others can be
applied to the soil as a preventative measure. These are commonly called “pre-emergent herbicides.“ The timing of
application is also crucial, since different chemicals work the best when
applied before, during, or after a crop has been planted.
Now that we know how herbicides are
used, it’s good to understand that they aren’t the sole solution in the war
against weeds. Herbicides are only one of the tools found in the producer’s
weed-fighting toolbox. Other methods of weed control include cultural,
biological, and mechanical tactics. It’s recommended that farmers utilize
an Integrated Weed Management plan to best control weed
population. If the same type of herbicide is used in fields repeatedly,
agriculturists face the fear of weeds developing a resistance to the chemical.
A herbicide resistant plant develops through slight mutations in the plant’s
seed, which occurs due to the large quantity of seed produced by a single weed.
It seems to be a never-ending fight of producers against weed’s continuous
adaptability.
Modes
of Action
Herbicides can be further arranged with
the various methods of how they target the anatomy of plants. Mode of action
states the effect on the plant, and site of action specifies where the
herbicide targets the process. Most herbicides are designed to interfere with
an enzyme used to carry out an essential function to plant life
(photosynthesis, amino acid production, lipid production, etc.).
Roundup is a common herbicide that
belongs to group 9. This means it targets the enzyme referred to as EPSP
Synthase. This messes up the shikimate pathway, which would normally help produce
molecules such as amino acids. This completely ruins the plant’s physiology,
leading to its soon demise. If the chemical was formulated correctly, the plant will exhibit yellow and deformed leaves before
necrosis, or plant tissue death.
Another common herbicide is 2,4-D which
belongs to group 4 and is a growth regulator. All growth regulators affect the
levels of auxin within plants, which is a hormone that facilitates plant
growth. When applied correctly, the affected plant will exhibit twisting,
abnormal growth, and structural deformity before necrosis.
I could go on for pages describing in
detail why each group is unique, but this PDF is a useful and condensed resource. To
cut the long story short, it’s important for producers to choose a treatment
plan that implements various modes of action to further prevent weeds from
becoming resistant.
Real-Life
Application
Genetic modification has allowed
producers to use a wider range of herbicides on their crops, the most recent
scenario being dicamba. Dicamba is a group 4 growth regulator
that targets broadleaf plants. This chemical used to be more common in
residential areas (such as golf courses) than in row crop fields. It’s been
around in the US since the 1960’s, and up until 2016 farmers only used it to
eliminate broadleaf weeds before the growing season began. Dicamba is seen as
one of the more dangerous herbicides due to its ability to volatilize and move
post-application. This is why it’s now classified as a restricted use pesticide, which means there are
increased rules and regulations surrounding
application methods and timing. With the commercialization of dicamba-tolerant
soybeans, these farmers are now able to use dicamba on their beans (which are
broadleaves) without damaging them. When producers utilize biotechnology such
as dicamba-tolerant
soybeans and Roundup Ready corn, they are given another tool to
fight the persistent army of weeds.
The last thought I’d like to leave you
with regards the rate of application of herbicides. Let’s talk a bit more about
the herbicide commonly referred to as Roundup. Roundup (also known as
Touchdown) contains glyphosate as the active ingredient. All applicators must
follow the product label to properly calculate application rates. When using
Roundup it’s recommended to use 32 fluid ounces per acre, up until the
weed is one foot tall. Putting that into a bit of perspective – one aluminum
can of soda holds 12 fluid ounces, so this rate calls for less than 3 cans. Now
spread that out over an acre, which is approximately one football field.
Additionally rates and various chemicals mixed together vary upon the species
and maturity of weeds in the field. Simply put, these chemical applications are
highly technical, tightly regulated, and extensively researched.
by Rosie
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