Herbicide treatments for controlling invasive bush honeysuckle in a mature hardwood forest in West-Central Indiana
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Asian bush honeysuckles (Lonicera maackii [Rupr.] Maxim, L. morrowii Gray, and L. tartarica L.) have proved extremely invasive in eastern hardwood forests. In addition to displacing native forest ground flora and associated fauna, these understory shrubs pose a threat to forest regeneration. Effective control strategies need to be developed to incorporate into routine silvicultural prescriptions for affected stands. This study tested ten control treatments in a fully stocked, mature central hardwood forest in central Indiana for efficacy and cost. Treatments included: low volume foliar applications of 4 percent triclopyr (Garlon 3A), 3 percent triclopyr (Garlon 3A) + 1/8 percent imazapyr (Arsenal), and 5 percent glyphosate (Glypro Plus), each applied in both early spring and late fall; full basal bark application of 20 percent triclopyr (Garlon 4) in AX-IT basal oil; streamline basal bark application of 20 percent triclopyr (Garlon 4) in AX-IT basal oil; and cut stump treatments with either picloram + 2,4-D (Pathway) or 20 percent triclopyr (Garlon 4) in AX-IT. Treatment timings were chosen to test effectiveness of herbicide control at a time of year when native vegetation would be least vulnerable to off target damage. Efficacy was tested across four shrub size classes. All but one of the low volume foliar applications were equally effective, controlling 70 to 94 percent of bush honeysuckle shrubs between 2 and 8 feet tall. Triclopyr applied in the fall (Nov. 2) provided only 2 percent control. Both basal bark applications provided inconsistent and poor control. Both cut stump treatments were equally effective on the larger two size classes of shrubs, but efficacy declined on smaller shrubs due to operational difficulties of locating all shrubs in a treatment unit. Depending on bush honeysuckle stand stocking and size distribution, treatment costs ranged from $83 per acre to $383 per acre.