Glyphosate and glufosinate are now options for postemergence weed control in herbicide-resistant corn and soybean. Velvetleaf is one of the more difficult to control annual weeds with these herbicides at commonly used rates. Ammonium sulfate (AMS) is generally used with these herbicides to overcome hard water antagonism and to increase herbicide activity. Greenhouse and field trials were conducted with commercial adjuvants that might substitute for AMS. The adjuvants were evaluated in deionized water, tap water, and deionized water containing 500 mg/L CaCO3. In the absence of AMS, hard water reduced velvetleaf control with both herbicides. Regardless of water source, AMS increased velvetleaf control with both glyphosate and glufosinate. Several adjuvants increased velvetleaf control with either herbicide; however, none were superior to 2% w/v AMS. Other adjuvants decreased velvetleaf control with either herbicide.
Nomenclature: Ammonium sulfate; glufosinate; glyphosate; velvetleaf, Abutilon theophrasti Medic #3 ABUTH; corn, Zea mays L. # ZEAMA; soybean, Glycine max (L.) Merr. # GLYMA.
Additional index words: Ammonium sulfate, glufosinate, glyphosate.