Phenology of Vaccinium spp. in a black spruce (Picea mariana) plantation in northwestern Ontario: possible implications for the timing of forest herbicide treatments

Abstract

This study reports on the phenology of 180 vegetative and 180 reproductive shoots of lowbush blueberry (Vaccinium angustifolium Ait.) and velvet leaf blueberry (Vaccinium myrtilloides Michx.) in a young black spruce (Picea mariana (Mill.) BSP) plantation near Thunder Bay, northwestern Ontario. Leaves of both species emerged in mid-May and remained uniformly green until mid-August. By late August, the majority of tagged shoots had turned red and were beginning to deteriorate. Approximately 30% of tagged shoots lost their leaves by 25 September in both V. angustifolium and V. myrtilloides. Patterns of leaf development in V. angustifolium and V. myrtilloides suggest that Vaccinium spp. may be less susceptible to foliar-applied herbicides if applications are made during or following the period of leaf senescence (i.e., between late August and late September). However, delayed treatment may be impractical in conifer plantations, since the time of leaf senescence and abscission of blueberry coincides with that of many target species.