Thursday, April 8, 2010
Be Aware of Weed Resistance in Your Fields
There are now 341 herbicide-resistant weed biotypes reported worldwide, and 130 of those are in the U.S.
Nine weed species in the U.S. now have confirmed resistance to glyphosate. These weeds are strains of common ragweed, common waterhemp, giant ragweed, hairy fleabane, horseweed, Italian ryegrass, johnsongrass, Palmer amaranth and rigid rygrass.
Look for these resistance signs when monitoring your fields for weeds:
Has the field been sprayed repeatedly with the same herbicide or herbicides with a similar mode of action?
Is there a patch of weeds which occur in the same area year after year and is spreading?
Is there a particular weed type whish is no longer controlled?
Do you have surviving weeds of the problem species that may be in a patch where some are dead and some exhibit variable symptoms, but all are approximately the same age?