Evaluation of Preemergence and POST-directed Herbicides on Rootstock Safety in Field-grown Almond Nursery Stock

Abstract

Producers of fruit and nut tree nursery stock need effective weed control for maximum production of vigorous, high-grade planting material. Current weed practices include methyl bromide fumigation, preemergence herbicides, hand labor, and multiple tillage operations. As methyl bromide use is phased out due to air quality concerns, and fuel and labor costs continue to increase, herbicides are likely to become even more important for weed management in the nursery industry. Before new herbicides can be registered and used in stonefruit (Prunus sp.) tree nurseries, weed control efficacy and crop safety data are needed under local conditions. Eleven experiments were conducted from 2007 to 2011 in California tree nurseries to evaluate the crop safety of preemergence (PRE) and postemergence (POST-directed) applications of various herbicides on commonly grown peach (Prunus persica), plum (Prunus domestica), and peach/plum hybrid rootstocks budded to almond (Prunus dulcis) scions. Rootstocks grown from cuttings generally were more tolerant to herbicides than those grown from seed. Crop safety was adequate in seeded and vegetatively propagated rootstocks with oryzalin, pendimethalin, and isoxaben, all of which are labeled for use in tree nurseries. The unregistered herbicides, dithiopyr, rimsulfuron, oxyfluorfen, and foramsulfuron; as well as lower rates of indaziflam and penoxsulam; applied PRE and POST-directed can provide good to excellent weed control in some stonefruit rootstocks. However, because slight crop injury was occasionally observed, additional work on application rates, timing, and method of application, especially on nonlabeled herbicides is needed before these materials can be considered for registration and broad scale use in tree nurseries.