NUTRITIONAL STATUS AND INFESTATION IN Pseudotsuga menziesii BY SWISS NEEDLE CAST (Phaeocryptopus gaeumannii) AT AQUIXTLA, PUEBLA

Abstract

Pseudotsuga menziesii (Mirb.) Franco covers 10% of the total area of Christmas tree commercial plantations in Mexico. Swiss needle cast (SNC) is a disease particular to the genus Pseudotsuga, caused by the fungus Phaeocryptopus gaeumannii (T. Rohde) Petrak (1938). The main symptoms include chlorotic foliage and premature abscission of infected needles, resulting in thin crowns. The objective of this study was to determine the relationship of chemical fertilizer and tree nutritional status to severity and incidence levels of the disease. The hypothesis was that nutritional status correlates with variations on SNC infestation level in P. menziesii. The study was set up in the multipurpose forested land “El Manantial” in Aquixtla, Puebla. Treatments were fertilization with urea and potassium sulphate, and a chemical phytosanitary control with propiconazole and prochloraz. The experimental design was generalized random blocks, evaluating two controlled factors with three levels (factorial 3²) and, as the confounding or blocking factor, the visual level of crown transparency associated with SNC. Incidence and severity were evaluated. The results of the ANOVA did not indicate significant differences. Of the nutrient variables, those that had higher association with severity and incidence were Ca and Mn contents, and to a lesser degree, Cu, Mg and N. Among the treatments, antagonisms and synergisms were observed to affect nutrient status. Fungicides affected nutrient absorption, transport, and assimilation.