Production | Winter 2010
Words of the trade.
Farming today often involves a rudimentary knowledge of chemistry. Producers quickly get up to speed on the herbicide products they use and the terminology surrounding them, but they may not have a clear understanding of what all the terms mean. Below is a list of common terms associated with herbicides, and their definitions.
Mode of Action
This phrase is often associated with resistance management, and refers to the way in which a plant
is affected at the cellular level. Herbicides classified under the same mode of action move through
the plant in the same way (often referred to as translocation), with the same symptoms of injury.
Selective herbicide
These herbicides attack certain types of weeds/plants, while leaving others primarily untouched.
Whether a herbicide is called selective may also depend on the time applied, the environmental
conditions, how the product is applied, the stage of growth, chemical formulation or the rate applied.
Non-selective herbicide
These herbicides will harm or kill all plant material when applied. However these may become selective,
for example, if the rate of application changes.
Systemic herbicide
Systemic herbicides are absorbed at one of two points — in the leaves or by the plant roots. The
herbicide is then translocated throughout the plant to cause the desired damage. Systemic herbicides
can be used to battle both annual and perennial weeds.
Contact herbicide
Contact herbicides are most commonly used to tackle annual weeds. As the name implies, they only
affect the point of the plant that is actually touched by the chemical.
ACCase inhibitor
These herbicides interrupt enzyme activity that is needed for fatty acid synthesis, which allows
the weed to continue to grow. By inhibiting the enzyme activity, ACCase inhibitors stop cell membrane
production in the plant.
ALS Inhibitors
These herbicides essentially starve affected plants by interrupting the absorption of amino acids.
In the end, it doesn’t allow the DNA in the plant to fully synthesize. ALS inhibitors are among
the safest herbicides as the ALS pathway does not exist in animals.
Bleachers
Bleachers are part of a new herbicide group known as HPPD inhibitors. These products stop production
of protective pigments that allows ultraviolet light to destroy chlorophyll, preventing photosynthesis.
This results in the plant tissue turning white, with the effect that the colour has been bleached
from the leaves.
Active Ingredient
This refers to the compound within a herbicide that is responsible for its chemical activity. FF
