Comparing Various Methods of Predicting Development of the Spruce Budworm, Choristoneura fumiferana, in Northern Minnesota

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Abstract
Two climatological and two phenological methods for predicting spray application dates were compared. These were: degree-hour temperature summation, day-degree temperature summation, actual shoot growth of balsam fir (Abies balsamea (L.) Mill.), and 15% of shoot growth of balsam fir. Because the degree-hour method predicted the date of the peak of the 3rd instar precisely in each of 4 years, it was considered the more accurate method. On the other hand, the day-degree method was never more than 1 day off from the peak of the 3rd instar and was much easier to calculate; it was therefore deemed the more practicable method. Both phenological methods were less accurate and more variable.