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Abstract
A field trial was conducted on Vancouver Island to evaluate the efficacy of the native fungus Neonectria neomacrospora as a biocontrol agent of hemlock dwarf mistletoe (Arceuthobium tsugense), a conifer parasite. Treatments consisted in formulated inoculum of N. neomacrospora applied to unwounded and wounded A. tsugense swellings. After 10 months, the amount of bark necrosis for the wounded, inoculated treatment was significantly greater than for the other treatments. Similarly, sporodochia were more common (present on 50% of swellings) for the wounded, inoculated treatment than the other treatments (present on less than 10% of swellings). Neonectria neomacrospora was isolated from 55.0% of unwounded, inoculated swellings and from 73.7% of those wounded and inoculated, while isolated from 20.0% of unwounded, uninoculated swellings and from 35.0% of those wounded and uninoculated. These results suggest that, although some infection does occur when inoculum is applied to unwounded swellings of hemlock dwarf mistletoe, wounding significantly enhances infection. Hemlock dwarf mistletoe swellings with confirmed N. neomacrospora infection (isolation of the fungus and (or) presence of sporodochia) had their numbers of healthy mistletoe shoots significantly reduced (by 1.6, or about 36%) when compared with mistletoe swellings with unconfirmed infection (P = 0.014).
