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

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, untrea...