A two year field study was conducted in 1991 and 1992 to evaluate the sensitivity of landscape trees to certain turf herbicides as affected by mulch. The study included four tree species (‘Bradford’ callery pear, crape myrtle, Eastern redbud, red maple), four mulch treatments (shredded hardwood bark, pine bark, pine needles, no mulch), and six herbicide treatments [Banvel (dicamba), BAS 514 OOH (quinclorac), Image (imazaquin), Redeem (triclopyr), Stinger (clopyralid)]. Herbicides were applied as directed sprays at the labeled rates for use on turf. Visual injury (%) ratings were measured at 30, 60, 90, 120, and 150 days after treatment. Trunk diameters and total plant fresh weights were measured at the conclusion of the study. In most cases, applying the herbicide over mulch decreased tree injury compared to applications to bare soil (Fig. 3). Red maples were most severely injured by Stinger (clopyralid) (27%) (60 DAT) and BAS 514 OOH (quinclorac) (33%) (60 DAT). Redbuds were most severely injured by the same two herbicides, but at 89% (120 DAT) and 73% (120 DAT), respectively. ‘Bradford’ pears were injured by Banvel (dicamba) (32%) (120 DAT), and crape myrtles by Image (imazaquin) (10%) (120 DAT).
2Graduate Research Assistant and Professor, respectively.