A comparison of three foliar-applied herbicides for controlling mountain laurel thickets in the mixed-oak forests of the central Appalachian Mountains, USA

In the Appalachian Mountains of eastern North America, mountain laurel (Kalmia latifolia) thickets in mixed-oak (Quercus spp.) stands can lead to hazardous fuel conditions, forest regeneration problems, and possible forest health concerns. Generally, land managers use mechanical means or prescribed fire to control mountain laurel thickets, but these treatments are expensive, dangerous to implement, or have short-term effectiveness. From 2012 to 2016, we compared the effectiveness of three herbicides applied as broadcast foliar treatments at varying rates and in different months for reducing mountain laurel thickets. Triclopyr (ester formulation) top-killed mountain laurel within a few weeks at most month/rate combinations, but subsequent sprouting reduced overall effectiveness by year 3. Conversely, imazapyr provided little initial control of mountain laurel, but by year 3, the herbicide had killed nearly all the treated shrubs with no subsequent sprouting regardless of the month of application or rate. Glyphosate had limited effectiveness; spraying in August at 8 and 12 L/ha killed the mountain laurel over 3 years with little sprouting while all others treatments had little or no impact. From these results, it appears that several month/rate combinations of all three herbicides have potential for controlling mountain laurel thickets and merit further testing to refine application procedures.