The blackheaded budworm (Acleris gloverana) is one of the most destructive defoliators in coastal B.C. Population levels periodically reach outbreak levels at 10 to 15-year intervals and outbreaks have been recorded since the 1930s. Western hemlock and true firs are the preferred hosts but spruce and Douglas-fir can also be fed upon. All ages are susceptible.
Overview of blackheaded budworm defoliation on Vancouver Island.
The western blackheaded budworm prefers to feed on the upper crowns of dominant and codominant trees. Trees can be completely defoliated from a heavy attack, and severe defoliation can result in growth reduction and susceptibility to other biotic or abiotic forest health factors. Successive years of severe defoliation may result in tree mortality. Defoliation is visible in the summer and from a distance the defoliated trees will have a reddish-brown hue. Other defoliators such as the western spruce budworm cause similar damage.
Two-year Cycle Budworm
The two-year cycle budworm (Choristoneura biennis) is found in subalpine and boreal forests of B.C.'s Interior. The primary hosts are subalpine fir and white/Englemann spruces. All ages of trees are susceptible.
Two-year cycle budworm larvae initially mine the needles, buds and new cones, and feed on current foliage after bud flush. Older larvae prefer feeding on the current foliage but will feed on older foliage if current foliage is depleted. Damage is the heaviest in the second year of larval feeding. Feeding takes place from late April through June. The crowns of damaged trees appear reddish-brown from June to September. Several successive years of severe defoliation can cause mortality, particularly on immature or suppressed trees. Other damage includes top-kill, reduced seed production due to damaged cones, and height and volume loss.
Damage can be confused with other defoliators such as early feeding by the tussock moth or several species of cone worms. The different host species and provincial distribution distinguish the various species of budworm from each other.
Black Army Cutworm
Black Army Cutworm (Actebia fennica) feeds on a range of plants and also feed on conifers seedlings planted on recently burned sites. Black army cutworm was a major pest in the 1980s when prescribed burning was used for site preparation. With a reduction in the use of prescribed burning there had been a decrease in the impacts of black army cutworm. However, with an increase in wildfire activity across the province, there has been an increase in black army cutworm activity on recently planted sites.
Black army cutworm has one generation per year. Adults (moths) lay their eggs on recently burned sites starting in mid-July to September. The eggs hatch and larvae overwinter in the soil, and emerge to feed in the spring (May/June). Larvae are velvety black on top with white lines along their sides and their undersides are grey in colour. They range in size from 0.5 - 4.0 cm.
Black army cutworm damage is most significant two years following late season wildfires (July - October) and one year after an early season wildfire (before July). Seedlings planted on recently burned sites with little or no vegetation are more likely to sustain more feeding damage from cutworm larvae. It is recommended that planting of recently burned sites is delayed to three years after a late season fire or two years after an early season fire. Planting after vegetation has flushed can also reduce impacts on seedlings. Pheromone monitoring can also be used as an early warning system the year before planting. Multipher traps should be set-up by the first week of July, collected mid-September and checked regularly throughout the summer.
Black army cutworm feeding typically occurs in patches and damage to seedlings may vary by species. Most seedlings can sustain moderate defoliation with limited impact on growth or survival. Many factors will impact seedling survival and therefore it is recommended that follow-up surveys are completed one year after cutworm damage to assess survival and to determine if fill planting is required.
Identify and learn more about conifer defoliators: