Mark VanGessel, Extension Weed Specialist; mjv@udel.edu
We have had conditions that have resulted in a lot of tender plants. This, coupled with many fields needing postemergence herbicides, means we need to pay attention to adjuvant selections. Adjuvants are needed to increase herbicide coverage, increase adsorption across leaf surfaces, and improved performance. However, this can also increase the risk of crop injury. So consider:
- If the crops are tender and more susceptible, then weeds are also likely to be more susceptible (meaning weeds of the same size are more susceptible under these types of conditions). It may not be necessary to use the same level of adjuvants as you would for the same size weed under drought conditions.
- What is included in the tankmixtures? Tankmixing can increase risk of injury. Other pesticides can increase risk injury and many of the glyphosate products contain their own adjuvant systems. Also, some herbicide formulations may have similar properties to an adjuvant (i.e. emulsifiable concentrates can have adjuvant properties and add to the adjuvant load).
- What is required on the pesticide labels? Given a choice of adjuvants, non-ionic surfactants (80:20) are safer than crop oils or methylated seed oils. Also, given the choice of nitrogen sources, dry ammonium sulfate has less risk than liquid nitrogen fertilizer.
Be sure to match the adjuvants you use to the growing conditions, and the weeds and crop susceptibility at time of application.