Nursery growers have had a longstanding battle to control weeds in environmental horticulture crops. Oxalis (Oxalis spp.) is one of the most difficult weeds to control in container grown ornamentals. It grows aggressively in containers and can outcompete ornamental crops for water, nutrients, and light. Several chemical tools are available for preemergent control. However, there remains a need for effective control of emerged weed seedlings. At the 2007 Environmental Horticulture Workshop, IR-4 initiated a study to determine whether preemergent herbicides could provide efficacy for oxalis, and other weeds, up to the 2-4 leaf stage. Research was conducted from 2008 through 2019. This report is a brief summary of available data from 27 experiments received through the IR-4 Environmental Horticulture Program. Early postemergence applications of Casoron, Certainty, Dismiss, Gallery, Marengo/Indaziflam, SureGuard, Tower and V-10142 provided significant impact on emerged oxalis (Oxalis spp.). These findings benefit growers by identifying select preemergence herbicides which control specific weeds at early emergence stages in container grown ornamental horticulture crops.
