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A. Field development of Bacillus Ihurillgiellsis 239
I. U .Img. These concentrates included various additives designed to improve deposit
efficiency and adherence to foliage (rain fastness), and to prolong residual activity of the
biological agent.
Three field formulations were developed at the Laurentian Forest Research Centre,
and have been used experimentally in Quebec. The first formulation, based on an
aqueous solution of sodium dihydrogen phosphate (NaH 2P04), and the second, based
on an aqueous solution of sorbitol, incorporate chitinase and Chevron® sticker (Chevron
Chemical (Canada) Ltd.), and have been used since 1973 in low-volume sprays
(4.7 l/ha). Sorbitol is a humectant, whereas sodium dihydrogen phosphate is added to
increase the specific gravity of the liquid B.t. formulation. The third formulation, named
Futura by the Laurentian Forest Research Centre, also uses sorbitol, chitinase, and
sticker but incorporates less aqueous carrier and has been used for reduced-volume
sprays (2.5 Jlha) since 1978 (Smirnoff 1980a, 1981a). Formulations used in Ontario and
the Atlantic Provinces were similar, but did not include chitinase, sorbitol, or sodium
dihydrogen phosphate (Morris 1980).
Smirnoff (1973, 1977) concluded after several years of experiments that the addition of
minute quantities of chitinase increases the efficacy of B.t. against spruce budworm; in
his view, it enhances penetration of ingested ingredients through the gut lining, and
rapidly potentiates symptoms of infection (lethargy, weight loss) even at low temperatures.
Some other additives have been tested for compatibility. Smirnoff (1981b) found that
either mineral oil in large quantities or various dyes inhibited spore development.
During 1970-79, Thuricide® 16B (Sandoz. Inc.) was the only product fully registered
for spruce budworm control under the Canadian Pest Control Products Act; around 1980
Dipel® 88 and Novabac® (Cyanamid Canada) have been fully registered.
Spray delivery systems and measurement of deposit
Sprays were applied by various aircraft ranging from four-engined freight planes to
single-engined biplanes and helicopters. They included the Lockheed Constellation L-
749, Douglas DC-6B, Canadair CL-215, Grumman Avenger TBM, Grumman Ag-cat,
Boeing Stearman, Piper Pawnee, Cessna Agtruck, and the Sikorsky S55-T helicopter.
Several kinds of spray emission hardware were tried, including Beecomist® (Beeco
Products Co., USA), Micronair® (Micronair (Aerial) Ltd., U.K.) boom and flat fan
Teejet® nozzles, and boom and open nozzles. Spray aircraft were calibrated to ensure
appropriate emission rates for prescribed swath widths. Swath width varied from 305 m
for a Constellation to 38 m for an Ag-cat (Smirnoff 1979a, Smirnoff & Juneau 1982).
There is no general agreement on the optimal droplet size or optimal foliage coverage.
Spray coverage is measured as the number of droplets per square centimetre on Kromekote®
cards, or as the number of colonies per square centimetre collected on agar plates
or MiIlipore® filters, placed at ground level in forest clearings. The number of spores
deposited per unit area on glass plates at ground level has also been measured (Morris
1980). In 1979, Smirnoff & Valero proposed a new method whereby a given volume of
peptonized water was exposed to the spray, so that the number of spores deposited per
unit area could be calculated. For B.t. treatments, this value is more important than the
total volume of liquid deposited (Smirnoff 1980a). Field tests have shown the necessity
for calibration of the spray system: assessment based on the viable spore count deposited
per unit area provides an adequate calibration.
The concentration of B.t. within the proprietary product, the properties of the
adjuvants added at the airstrip mixing plant, and the composition of the tank concentrate
all affect the rate of deposition and the success of operations (Smirnoff 1980b).
Operators used various kinds of spray hardware designed for chemical insecticides.
Beecomist® spray heads were satisfactory on the Sikorsky helicopter. However, a