Perennial Weed Control in Blueberries

Timothy W. Miller and Carl Libbey

WSU Mount Vernon NWREC


     Young ‘Draper’ blueberries, transplanted in September, 2011 (Craig Ford, South Alder Farms, Lynden, cooperator), were treated with directed sprays of Callisto (mesotrione), Matrix (rimsulfuron), Sandea (halosulfuron), Sinbar (terbacil), Stinger (clopyralid), Treevix (saflufenacil), Karmex (diuron), Lorox (linuron), Reflex (fomesafen), Alion (indaziflam), Dual Magnum (s-metolachlor), Gramoxone (paraquat), and Velpar (hexazinone) either during late dormancy (March 4, 2013) or post bud break (April 30, 2013; POST). The same plots were treated with the same herbicides in 2012. Plots in the first replicate were also inadvertently treated by the cooperator with a directed spray of Callisto in mid-April. Percent weed control from dormant-season applications was estimated April 24, 2013 and for all plots on May 13 and 28 and September 14, 2013. As these were young blueberry plants, no berries were harvested from these plots. The experimental design was a randomized complete block with four replicates. Means were separated using Tukey’s HSD (P < 0.05).


     Some weeds were emerged at the time the dormant application timing (early March). Primary weed species in the plots were common chickweed (Stellaria media), shepherd’s-purse (Capsella bursa-pastoris), purple deadnettle (Lamium purpureum), white clover (Trifolium repens), common groundsel (Senecio vulgaris), spring whitlowgrass (Draba verna), and annual bluegrass (Poa annua). Other weeds included prostrate knotweed (Polygonum aviculare), panicle willow-herb (Epilobium ciliatum), dandelion (Taraxacum officinale), quackgrass (Elymus repens), and corn spurry (Spergula arvensis).


     Weed control at about 6 weeks after the dormant treatment (April 23) was excellent, ranging from 87 to 100% (Table). Note that products listed as “POST” in the Table were not applied until May 2, 2013 but those plots had received the same treatment during the 2012 season. Those treatments ranged from 62 to 88% control, although none differed significantly. Weed control at the May 13 evaluation ranged from 48 to 100%, with Reflex at 1 pt/a or Stinger alone (during dormancy or POST) or POST with Sandea resulting in <72% weed control. By May 28, the only treatments resulting in <70% weed control were the same treatments as well as Treevix at 2 oz/a, Reflex at 2 pt/a; control with Sandea + Stinger POST had improved to 87% at that timing. There were still no significant differences in weed control among the treatments by September, although it was clear that the rows had been treated with Gramoxone by the cooperator during the summer to control emerged weeds throughout the plots. No treatments caused visible blueberry

foliar injury at any evaluation.


     Based on these data, continued testing of these product combinations is warranted. In particular, Treevix and Alion remain as high priorities for registration in nonbearing and newly-planted blueberry, and Reflex also appears to be a good fit for these uses.