Assessment of sanitary conditions in stands of Norway spruce (Picea abies Karst.) damaged by spruce bud scale (Physokermes piceae Schrnk.)

Spruce bud scale (Physokermes piceae Schrnk.) affects tree growth directly and indirectly. Direct injury appears in the form of tissue damage, as insects suck sap from tree phloem. Indirect injury appears as “honeydew”, which results in negative effects on tree growth. Plant sap is saturated with various carbohydrates called photosynthates that are difficult for scaly insects to digest. Therefore it is secreted in excrements, which are subsequently a food source for the black sooty mold (Apiosporium pinophilum Fuckel). The fungus covers needles blocking stomata, causing decreased transpiration and photosynthesis. An inexplicable wither of Norway spruce was reported in Latvia during 2010 due to black sooty mold. However, spruce bud scale was not evident. In 2011, mass propagation of spruce bud scale was observed following the 2010 Norway spruce loss. One objective of this research was to determine if Kraft tree growth classes could be applied to establish the factors responsible for tree foliage damage. Six 21 - 40 year old (second age class) Norway spruce stands were evaluated. Two circular sample plots with a 7.98 m radius, and a 200-m2 area were randomly established per each forest stand hectare. Diameter at breast height (dbh, 1.3 m), and height of approximately 30 trees was measured to model a trend. For all trees, Kraft class, and foliage damage level caused by spruce bud scale and black sooty mold were determined. Significant differences were not observed in tree damage levels among stands, however significant differences among damage levels in different Kraft classes were detected (F = 3.45 > Fcrit. = 2.80, α = 0.05 > P = 0.02) found. Overall damage intensity was 29.3 %. Total forestry loss was 1153 LVL (1640 EUR) for all surveyed stands (10 ha), and 115 LVL (164 EUR) per hectare.