Auxin Herbicide Drift Injury on American Elderberry Plants Influenced by Growth Stage

Abstract

The use of low-volatile 2,4-D and dicamba products on herbicide-tolerant crops has resulted in cases of offtarget movement and injury to sensitive plants. An outdoor nursery and a greenhouse experiment were conducted to determine the herbicide sensitivity of potted American elderberry [ Sambucus nigraL. subsp. canadensis(L.) Bolli] plants at a vegetative (V), tight green cluster (TGC), or full bloom (FB) stage. For the nursery experiment, one rate corresponding to 1/20 of the manufacturer’s labeled rate of 2,4-D (1.06 kg ae·ha-1) or dicamba (0.56 kg ae·ha-1) was applied, whereas 1/20 and 1/200 rates of these herbicides were used in the greenhouse study. For plants treated at the V stage, necrosis was observed at the stem apex of some canes treated with either herbicide at the 1/20 rate. For the 1/200 rate, 2,4-D applied at the V stage resulted in a slight hormetic effect on cane growth compared with the nontreated control by 8 weeks after treatment (WAT). Elderberry plants were generally more sensitive to floral abortion when treated with an auxin herbicide at TGC versus the FB stage. For the 1/20 rate in both studies, 2,4-D caused floral distortion or complete abortion of umbels of 50 to 100% of canes, whereas dicamba caused complete abortion on 10 to 40% of the canes when applied at the TGC stage. For the remaining canes that produced fruit, yield and juice/umbel was reduced by both herbicides at the 1/20 rate. In contrast, herbicides applied at the 1/200 rate at TGC had no effect on fruit yield and juice/umbel compared with the nontreated control in the greenhouse study. Also, plants treated at TGC with 2,4-D at the 1/200 rate (no fruit produced on plants at the 1/20 rate) or dicamba at both rates had lower juice soluble solids concentration (SSC) and SSC/titratable acidity ratios than those from nontreated controls. Herbicide residue was present in juice from all fruiting plants when treated at TGC or FB, but the amount detected in juice from plants exposed at FB to 2,4-D at the 1/20 rate (391 ppb) exceeded the allowable tolerance level for elderberry.