Kalmia angustifolia is a problematic understory shrub in boreal forests of eastern Canada. In this article, we discuss the nature of its interference with conifer regeneration, and control measures using herbicides. Although laboratory studies suggest the leaching of water-soluble phenolic compounds from Kalmia, allelopathic interference cannot be invoked as a cause of conifer regeneration failure because of lack of field evidences. Because of severe inhibitory effects of Kalmia on conifer growth and its role in long-term habitat degradation, the development of strategies for Kalmia management is a priority research area. Neither prescribed burning, plowing, scarification, nor 2,4-D application was proven effective in Kalmia control. Two studies were carried out using transplanted Kalmia to determine the efficacy of several herbicides and a herbicide plus burning treatment to control Kalmia. In one experiment, eight treatments were applied. They were control, glyphosate (3.36 kg/ha), glyphosate (2.88 kg/ha) plus surfactant Tween 20 (0.2%), glyphosate (2.88 kg/ha) plus surfactant Triton XR (0.2%), fosamine ammonium (5.38 kg/ha), triclopyr (4 kg/ha), hexazinone (2.2 kg/ha), and hexazinone (5 kg/ha). Triclopyr (4 kg/ha) provided the best control with significant reduction in the number and dry weight of sprouts, rhizomes, and current-year foliage of Kalmia compared with control. In another experiment, triclopyr (4 kg/ha), hexazinone (5 kg/ha), and hexazinone (2.2 kg/ha) plus burning treatments were applied. To determine the response of black spruce seedlings to the herbicide treatments, black spruce seedlings were planted in all the Kalmia pots except the ones that received the hexazinone (2.2 kg/ha) plus burning treatment. Triclopyr (4 kg/ha) caused the maximum damage to Kalmia, affecting all the above- and below-ground components of the plant. We recommend that an experimental field trial be established using triclopyr to test its efficacy for Kalmia control under field conditions.

Nomenclature: Glyphosate; fosamine ammonium; triclopyr; hexazinone; Triton XR; Tween 20; Kalmia, Kalmia angustifolia (L.); black spruce, Picea mariana (Mill.) BSP.

Additional index words: Allelopathy, regeneration failure, surfactants.