Why does glyphosate not work on resistant weeds?
When a field has a growing number of the resistant weeds, their genetics can spread by harvesting equipment or tillage equipment, or animals, wind and water. Since the palmer amaranth is either a male or female plant, the pollen from the male plants can travel as far as 1,000 feet from a resistant male to a susceptible female and pass along the genetics for resistance.
Another problem weed is marestail, but the mechanism for resistance is not the same as the amaranth. In marestail the glyphosate is kept in one part of the plant, and the other parts are unaffected and continue to grow with the help of a dominant or semi-dominant gene. And because marestail is capable of both self pollination and cross pollination, the resistance can occur rapidly in a group of plants.
So what do you do? The NE researchers say the movements of resistant traits do not observe property lines, managing the resistance problem is the challenge for all farmers, and that means knowing the weeds in your field and implementing weed management programs that are both economically effective and capable of reducing the overall resistance. They recommend the use of a pre-emergent herbicide that is effective against most of the weeds in the field, followed by a post emergent herbicide that is effective against the same weeds. They say the use of multiple products will result in delayed evolution of herbicide resistance populations.
A growing number of weeds have become resistant to glyphosate for different reasons. Amaranth is able to overcome the glyphosate’s designed destruction of an enzyme that makes amino acids, while marestail has a gene that corrals glyphosate in a single area of the plant to keep it away from reproductive areas. Resistant plants can either spread their pollen great distances or reproduce resistance themselves. A farmer’s options for overcoming the problem are the use of pre and post emergent herbicides that are alternatives to glyphosate.
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