Effects of Naphthaleneacetic-Acid Sprays on the Development and Drought Resistance of Pine Seedlings

Abstract

Different nursery beds of 1-year-old jack and loblolly pines, 2-year-old white pine, and 3-year-old red pine were sprayed in September, October, and March with naphthaleneacetic acid in concentrations of 200, 400, 600, 800, or 1000 mg. per liter of 1% Dowax emulsion. Other blocks of seedlings were toppruned at such a height as to remove most of the terminal buds and about 50% of the foliar surface. Chief results were: 1. Seedlings of white pine and red pine were not perceptibly affected by growth-regulator treatments. An explanation for this failure to respond is offered. 2. Jack pine seedlings sprayed in September with 800 and 1000 mg./l. were inhibited to the extent that on May 1 they had produced only 42% as much new shoot growth as controls. October and March sprayings, and September sprayings of lower than 800 mg./l., produced no discernible effects. 3. Loblolly pine seedlings sprayed in September responded to all concentrations above 200 mg./l., the degree of inhibition increasing with concentration. On May 18, seedlings treated with 800 mg./l. had produced only 10% as much new growth as controls. 4. New growth on top-pruned seedlings of both jack and loblolly pine was restricted almost as much as on the most heavily inhibited seedlings. 5. After being transplanted, both jack and loblolly pine seedlings inhibited with naphthaleneacetic acid showed lower resistance to drought than untreated seedlings. Top-pruned seedlings of jack pine were only slightly inferior to controls, and those of loblolly pine were only slightly better. The only lot showing a slight increase in resistance to drought was loblolly sprayed in September at 200 mg./l.