Adjuvants for Prohexadione-Calcium Applied to Alfalfa Interseeded into Corn

Application of the growth retardant prohexadione-calcium (calcium 3-oxido-5-oxo-4-propionylcyclohex-3-enecarboxylate; PHD) on interseeded alfalfa (Medicago sativa L.) improves its establishment under silage corn (Zea mays L.). This study evaluated the relative effectiveness of crop oil concentrate (COC), high surfactant oil concentrate (HSOC), methylated seed oil (MSO), and nonionic surfactant (NIS) as adjuvants for commercially formulated PHD (Apogee) when applied with and without supplemental ammonium sulfate (AMS). Acidified solutions of PHD (0.25 kg a.i.ha(-1)) plus adjuvants were sprayed on 23 to 27 cm tall glyphosate-resistant alfalfa seedlings that were interseeded immediately after corn planting at two sites in Wisconsin. All PHD-adjuvant-AMS combinations were equally effective, reducing alfalfa height by an average of 16% within 4 wk after treatment and increasing alfalfa stand counts after corn harvest by 30% compared with the non-PHD treated control. The results suggested a variety of adjuvants may be used when applying PHD to interseeded alfalfa.