Canadian Forest Service Publications
Bacillus thuringiensis subsp. kurstaki aerial spray prescriptions for balsam fir stand protection against spruce budworm (Lepidoptera: Tortricidae) 2004. Bauce, E.; Carisey, N.; Dupont, A.; van Frankenhuyzen, K. Journal of Economic Entomology 97: 1624-1634.
Issued by: Great Lakes Forestry Centre
Catalog ID: 25129
CFS Availability: PDF (request by e-mail)
Although commercial formulations of Bacillus thuringiensis subsp. kurstaki (Btk) are being widely used in forest protection against lepidopteran defoliators, optimal application prescrip tions have often yet to be worked out in detail.We conducted field experiments over a 6-yr period (1996-2001) in southwestern Quebec to determine application prescriptions for optimal protection of balsam fir, Abies balsamea (L.), healthy stands against the spruce budworm, Choristoneurafumiferana (Clemens) (Lepidoptera: Tortricidae). At moderate larval densities (<30 larvae per 45-cm branch tip), similarfoliage protection was achieved with one or two Btk applications of 30 billion international units per hectare (BlU/ha). When larval densities exceeded 30 larvae per branch tip, two successive applications of 30 BlU/ha significantly increased foliage protection. Whether the second application took place 5 or 10d after the first spray did not affect treatment efficacy. Increasing the application dosage from 30to 50BIU/had it not lead to better foliage protection against high larval densities, but the current standard dosage of 30BIU/hasaved more foliage than 15BIU/haagainst moderate populations. The recommended dosage of 30 BIU can be applied in lower application volumes (1.5 liters/ha) by using a high-potency product (20 BIU/liter), because we did not observe a reduction in efficacy comparedwith the application of a lower potency product (12.7 BIU/liter) in 2.37 liters /ha. We also demonstrated that Btk can be applied much earlier in the season without compromising sprayefficacy: there wasno differencein treatment efficacy of double applications at 30 BIU/ha when the first spray was timed for early third, peak third, or early fourth instars.