Technical
Glyphosate
Stay in control
It is important to understand how weed control works can help to get the best out of herbicides and increase efficiency, explains Manda Sansom, Monsanto’s Technical Manager
G
lyphosate is one of the most effective and widely used herbicides in the amenity industry, but a deeper understanding of weed growth and herbicide mode of
action can help operators get the best out of this important product.
Increasing pressure on groundcare regimes and unpredictable weather conditions can mean that herbicides are applied at the wrong time or in a less than efficient way, compromising effectiveness and the success of the weed control programme.
How glyphosate works
Glyphosate is a systemic, foliar acting herbicide which works by blocking the biochemical pathway responsible for protein synthesis in plants - the Shikimic Acid Pathway.
Before it can act, the glyphosate must first be taken into the plant and then moved in the sap/phloem to the growing points in roots and shoots where the protein production takes place. Death by starvation will follow.
There is no residual action in the soil and no root uptake, which makes it especially suitable for use in environmentally sensitive areas.
Apart from specialist recommendations for direct introduction by stem injection or stump treatment, by far the majority of successful
124 I PC JUNE/JULY 2015
weed control with glyphosate is reliant upon uptake through healthy foliage.
Why weed control can fail
Many factors will impact on the efficiency of weed control; from the quality of the glyphosate formulation to the application equipment, and from prevailing weather conditions to the growth of the target weed. The maximum kill effect can only occur when a fatal dose of glyphosate actually reaches the growing points. Following the product label recommendations is a must for best results.
Disappointing results usually arise for two main reasons. Either not enough herbicide reaches the target leaf during application, or not enough glyphosate is translocated from the leaf to the growing points.
A third reason sometimes suggested is that a weed has developed resistance to glyphosate. Although this is theoretically possible, it is the least likely reason and has not been confirmed in any weeds in the UK at this time.
One of the commonest ways of selecting for the development of tolerance or resistance in any weed is to repeatedly spray the same active ingredient at a sub-lethal dose. Thus spraying weeds with glyphosate at the optimum time and rate is also an essential part of any anti- resistance strategy.
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