Before an herbicide is registered for use, countless field trials and experiments are conducted to determine the lowest, effective use rate that consistently controls each target weed. The reason so many years and resources are dedicated to collecting this precise data is that deviation from labeled rates can cause severe problems. Applying more than the recommended rate can cause crop damage, and applying less can lead to herbicide resistance. That being said, using full, recommended herbicide rates is an integral part of any herbicide resistance management program.

Multiple studies have been conducted to identify the effects of using reduced herbicide rates. Drs. Paul Neve and Stephen Powles demonstrated that by repeatedly using reduced herbicide rates, resistant weed populations increased more compared to when a full, recommended rate of the herbicide was used.

After only three generations of selection pressure with reduced herbicide rates, Neve and Powles found rigid ryegrass biotypes that were six to 50 times more resistant than the original, non-selected biotype.

For further recommendations offered by Syngenta Crop Protection, view the full article on the cereals FarmAssist Web site.  You can also view a technical bulletin on using  full rates here.