E.G. Kettela
Executive Summary
In 1994 a series of spray trials were conducted to evaluate the quality and quantity of spray deposit of Foray 76B (containing Bacillus thuringiensis) in white spruce (Picea glauca) plantations. Efficacy on spruce budworm (Choristoneura fumiferana) was evaluated in four of the eight spray tests conducted. Two dosage rates and two aircraft spray heights were used and a total of eight spray sites were treated. A spray line method was used to apply the B.t and to evaluate spray deposit on foliage. The B.t was dyed with Acid Red #52 400 XB at a concentration of 0.2% w/w. Spray applications were done with a Cessna 188 equipped with four Micronair AU 4000 rotary atomizers and an AGNAV/REMSPEC system. The Micronairs were set to operate at maximum RPM's and with flow rates of 2 L/min/atomizer.
The tests showed that planned operating parameters, in reality, vary widely. Spray deposit vertically in the crown of sample trees was highest at the top and lowest at the bottom of the tree crowns by a factor of at least five. Spray deposits were similar on both white spruce and balsam fir (Abies balsamea) and the mean spray drop diameters were 62 um and 64 um respectively. Measurements of dimensions of new and old needle and conversion to square centimetre of foliage showed that deposit on new foliage was 2 to 7 times higher on the new needles, (the new needles were 1/2 the size of one year old needles), in spite of the fact that drops/needle were generally the same. Estimates of spray efficacy showed that Foray 76B at either 30 or 45 BIU/ha significantly reduced spruce budworm survival and defoliation. B.t (Foray 76B) can be expected to provide adequate foliage protection from spruce budworm feeding if sufficient deposit is attained at the feeding site.