Pitch Canker in Young Loblolly Pines: Influence of Precommercial Thinning and Fertilization on Disease Incidence and Severity

Abstract

Abstract Pitch canker disease affects southern pines, causing shoot dieback, stem deformation, and reduced growth. Disease occurrence is influenced by genetic resistance, abiotic and biotic environmental factors, and cultural practices. In young loblolly pine plantations with significant disease occurrence, options for disease control must focus primarily on silvicultural practices such as precommercial thinning or fertilization. In this study, cumulative disease incidence levels of 90-98% in the control, fertilize-only, and fertilize + thin treatments were reduced to 64% by precommercial thinning. Similarly, cumulative disease severity was reduced by 43% in the thin-only treatment. The positive effects of precommercial thinning on disease occurrence and severity were most evident during conditions of severe disease outbreak. Fertilization with potassium plus micronutrients did not suppress disease occurrence or severity and when combined with thinning, potassium plus micronutrients increased disease incidence by 50% over the thin-only treatment. The mechanisms responsible for these effects are not clearly understood but may reflect silvicultural influences on physiologically active defense mechanisms. South. J. Appl. For. 23(3):139-143.