Application of slow-release tablets to enhance white pine regeneration: growth response and efficacy against white pine blister rust

Abstract

Three field studies were established in northeastern Ontario to test the ability of slow-release tablets to provide prophylactic protection against white pine blister rust (caused by Cronartium ribicola J.C. Fisch.) and thereby improve the long-term survival, health, and growth of eastern white pine (Pinus strobus L.) seedlings. Experimental treatments included factorial rate combinations the fungicide triadimefon (Bayleton®), the insecticide imidacloprid (Merit®), and fertilizer (N–P–K, 15:8.5:3.75). Mean foliar fungicide residues increased to maximal levels (0.21 to 3.1 µg/g fresh mass (fm)) within 1 to 2 years posttreatment and declined markedly to <0.3 µg/g fm 3 to 4 years posttreatment. Dose-dependent and temporal trends observed in foliar residue levels were reflected by parallel trends in efficacy. At ≥2000 ppm triadimefon, infection rates were reduced to between 35% and 70% and mortality rates were reduced to between 6% and 52% over seven growing seasons across the three sites. In contrast, untreated seedlings had infection rates between 60% and 98% and mortality rates between 30% and 90%. Neither fungicide nor insecticide treatments had significant effects on surviving seedling growth. Differences in fungicide uptake, disease incidence, and seedling growth in response to fertilization were observed among the three sites. Direct weed control, provided at one site, appeared to offer relatively greater health and growth benefits than fertilization.