A successful Christmas tree production requires a good and effective weed management program. Most common weed control practices in Christmas tree production involve mechanical mowing and the application of chemical herbicides. Repeated applications of the existing herbicide options have resulted in the development of herbicide-resistant weed species. It is also important to test newer herbicides to expand the list of herbicide options. Hence the objectives of this research were to evaluate labeled (1X) and double (2X) rates of newer herbicides for weed control efficacy and for phytotoxicity in Fraser fir variety of Christmas tree. Field experiments were conducted in summer and fall 2024 at a commercial Christmas tree farm located at Gobles, MI. Christmas tree variety chosen for the experiment was four-year-old Fraser fir (Abies fraseri). The herbicide treatments included glyphosate trifloxysulfuron-sodium, glyphosate flumetsulam, glyphosate flumetsulam clopyralid, glyphosate chlorimuron, glyphosate cloransulam, glyphosate topramezone, glyphosate flumioxazin. Out of these treatments, the last two were considered as industry commercial standards. The control treatment included only glyphosate. All herbicides were tested for their labeled (1X) rates and double (2X) rates. Treatments were applied before bud break as directed application towards the lower 18 inches of the trees with a carbon dioxide backpack sprayer calibrated at 27 gallons per acre output. The experiments were complete randomized block design with four replications of each treatment. Data were collected at 1, 2, 3, and 4 months after treatment (MAT) which included visual estimation of weed control based on a scale of 0% to 100% (0% meaning no weed control and 100% meaning complete weed control) and phytotoxicity based on a scale of 0% to 100% (0% meaning no plant injury and 100% meaning complete death of a branch). Dominant weed species were recorded as well. Data were analyzed by ANOVA in SAS 9.4 and means were separated out by Tukey’s HSD test. Results showed that 1X rates of glyphosate chlorimuron and glyphosate trifloxysulfuron-sodium provided 70%-90% weed control till 4 MAT and their 2X rates showed no significant injuries to the Fraser fir variety till 4 months. Hence, glyphosate chlorimuron and glyphosate trifloxysulfuron-sodium can be additional options for Christmas tree growers for weed control in future. However, long-term multiple year studies are still required based on different herbicidal rates and on different varieties of Christmas trees for expansion of these herbicide labels.
