Tolerance of Young Blackberries to a Selection of Preemergence Herbicides and Rates

Limited preemergence herbicides are registered for new blackberry (Rubus subgenus Rubus) plantings. This greenhouse experiment was designed to investigate the effects of a broad selection of preemergence herbicides at multiple rates on blackberry transplants. Screening was initiated Aug 2021 and repeated Mar 2022 in Fayetteville, AR, USA, in a greenhouse at the Milo J. Shult Agricultural Research and Extension Center. ‘Ouachita’ blackberry plugs were transplanted into utility pots that contained field soil and growth media treated with preemergence herbicides. After transplanting, plant height was measured from the substrate to the highest apical meristem of 25 representative plants. Initial blackberry plant heights were 13.5 and 9.2 cm in 2021 and 2022, respectively. Twenty-five treatments were evaluated, consisting of 12 preemergence herbicides at 1× and 2× field rates, and one untreated control. Herbicide treatments included diuron, flumioxazin, halosulfuron, indaziflam, mesotrione, napropamide, oryzalin, pendimethalin, rimsulfuron, S-metolachlor, simazine, and sulfentrazone applied to substrate in containers at their respective 1× or 2× field rates. Data were collected on plant height, blackberry injury ratings, internode length, leaf chlorophyll content, and destructive harvest, including leaf count, leaf dry biomass, and aboveground dry biomass. Specific leaf areas and leaf area-to-dry matter ratios were calculated. When observed, plant injury tended to increase from 7 days after treatment (DAT) until 42 DAT. Greater injury levels were observed in response to treatment with mesotrione at the 1× (78%) and 2× rates (90%), halosulfuron at the 1× rate (58%), halosulfuron at the 2× rate (68%), and diuron at the 2× rate (73%). Injury from diuron was rate dependent, with the 1× rate causing relatively low injury (19%). At both the 1× and 2× rates, flumioxazin, indaziflam, napropamide, S-metolachlor, and pendimethalin treatments exhibited similar responses to the untreated control.