Influence of herbicide application volume on weed control in non-irrigated nursery production areas©

Preemergence (PRE) herbicides require activation with rainfall or irrigation within 1-3 weeks after application in order to perform effectively. During dry weather periods, erratic weed control may result if herbicides are not properly activated. In this study flumioxazin (SureGuard^® suspension concentrate) and indaziflam (Marengo^®), two PRE herbicides utilized in bareground areas of nurseries and as directed applications in larger containers (often not irrigated with overhead sprinklers), were examined at different application volumes to determine if increasing herbicide application volume could increase weed control in the absence of activation irrigation. Flumioxazin was applied at 8 and 12 fl. oz. acre^-1 while Marengo was applied at 7.5 and 15 fl. oz. acre^-1 to 1.3-L containers filled with a pinebark:peat substrate using application volumes of 5, 10, 20, 40, 60, 80, or 100 gal acre^-1 (gpa) for control of common nursery weed species. The most consistent control was achieved with the high rate of Marengo across all application volumes (91 to 100% control) while SureGuard provided the most consistent results across all application volumes at both rates, with percent control ranging from 61 to 84% control. It is recommended that growers use application volumes at least as high as or higher than suggested on herbicide product labels and still attempt to time applications when some rainfall is expected in the coming days if possible.