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Recommendations
A. Field development of Bilcilllls IllIlringiensis 245
or is forbidden to use conventional chemical insecticides for the control of the spruce
budworm". The main technical recommendations were as follows:
Objective - primarily to limit the average annual defoliation to less than 50% and
secondarily to reduce the numbers of spruce budworm by 75-85%.
Formulation - Thuricide® 16B. water (not chlorinated). Chevron® sticker (0.1 %).
Optional for experimental trials: Thuricide lt 32B. sorbitol. Chevron® sticker. chitinase
(9880 nephelometric units per hectare). water. and Erio Acid Red (experimental tracer).
Note that dyes may inhibit B.I. efficacy.
Dosage - 20 x 10" I.U. of B.I. in a minimum of 4.7 I/ha. In mixed spruce·fir stands. two
applications of 10-20 x 10" I. U .Iha each.
Operational constraints - pre·spray population density of 25-30 larvae per 45·cm branch
tip. Application should start at shoot flare and continue no later than the date when 30% of
the spruee budworm have developed to the fifth instar.
Deposit specifications - agar plates or Millipore® filters should be used to collect ground
level deposits. aiming for a density of 25 droplets/cm l or more.
In an attempt to reduce the inconsistencies of results in previous years, the 8.t.
applications using these guidelines were co-ordinated in 1979 and 1980 (Morris 1980,
1981). In general, the guidelines were followed unless extenuating circumstances were
encountered. Clearly, B.I. is an effective alternative to the use of chemical pesticides for
the protection of foliage. An analysis of the results of these applications (Morris 1980)
showed that successful treatments had the following common characteristics:
1. Pre-spray densities were usually less than 28 larvae per 45-cm branch tip
2. Larval development at spray time was around fourth instar
3. Bud flushing was 80-100% complete (except on red spruce)
4. LV. applied per hectare were 20-40 x 10" in single or double applications
5. Ground level droplet density was greater than 25/cm 1
6. Spray time relative humidity was mostly higher than 65%
7. Good weather followed spraying.
These conditions are now generally accepted by researchers as desirable for 8.1.
application in the forest.
Smirnoff (1980c) advocates further conditions for reducing costs and increasing success;
a) The required 8.1. dosage should be emitted in a formulation dispensible at
2.5-3.0 l/ha; or (in the case or Thuricide® 32B with sorbitol in water) at 4.711ba;
b) formulations should include Chevron® sticker at 1:1600; and chitinase at 10 000
nephelometric units per hectare;
c) spore viability in the concentrate drum should be checked;
d) large capacity aircraft equipped with boom and nozzle are more cost-effective
than small aircraft. Spray output must be calibrated and checked by counts of viable
spores at ground level; the ground deposit should attain at least 60% of the emission
rate;
e) B.t. treatments should be carried out when most ofthe larvae are third instar, and
buds are flushing (Smirnoff 1980c. Auger el 01. 1981).
Improvements in commercial formulations and application technology during the past
decade have brought B.I. to a point where it is now considered a clear alternative to
chemical insecticides for use against spruce budworm. especially in environmentally
sensitive areas. It is almost as effective for tree protection as the available chemical
pesticides. Success or failure cannot yet be totally explained or predicted because
relationships between foliage protection and dosage per volume emitted are not firmly
established. Moreover, estimates of ground deposits have borne little practical relationship
to deposits on foliage. The technical guidelines prepared in 1978 (see earlier)