Naphthenate stimulation of conifer growth over a 3-year period

Abstract

On May 1, 18, and 30, 1972, 1-year-old seedlings of Douglas fir (Pseudotsugamenziesii (Mirb.) Franco), lodgepole pine (Pinuscontorta Dougl.), Sitka spruce (Piceasitchensis (Bong) (Carr.), western hemlock (Tsugaheterophylla (Raf.) Sarg.), and also Douglas fir planted in plastic bullets were sprayed with a 2000- or 5000-ppm solution of potassium naphthenate (KNap). The growth stage of each species on each of the three dates was classified as (A) buds unopened, (B) terminal bud well open, little or no growth in stem length, or (C) terminal bud well open, lateral buds opening, growth in stem length just beginning. Eighty-six percent of the average cumulative stem-length increments of the groups of plants given the various KNap treatments, determined at the end of each of the 3 years after spray application, were greater than those of their respective control (untreated) plants. Maximum response of all species was to 5000 ppm KNap applied at growth stage C. One, 2, and 3 years after treatment the average cumulative growth in stem length of plants given this treatment exceeded that of controls by 44.5, 25.2, and 15.2%, respectively. The most effective treatment of Douglas fir in bullets was 2000 ppm KNap, also applied at growth stage C. The survival of treated seedlings at the end of the 3rd year did not differ significantly from that of controls. A second application of 5000 ppm KNap on May 18 of the 3rd year, at which date bud growth of the four species was in the early, middle, or late phases of stage B, was without significant effect.