Chemical thinning in blue spruce (Picea pungens Engelm.) stands and its effects on cambioxylophagous fauna

Abstract

Chemical thinning was applied in blue spruce (Picea pungens Engelm.) stands by the application of Roundup Klasik and Garlon 4 EC. The thinning efficacy of Garlon 4 EC was negligible, while that of Roundup Klasik reached nearly 100% when the full strength concentration was applied in quantities of 1 ml per 10 cm of stem girth using the method of drilling holes for the arboricide injection. Treated blue spruce trees died within 6 month after application. No difference was found in the response of silver and green varieties of blue spruce to the application of arboricides. Several species of cambioxylophages colonizing blue spruce were killed by Roundup. The economically insignificant Hylurgops palliatus (Gyll) was the most abundant negatively affected insect species found on the stem, followed by significant pests such as Ips amitinus (Eichh.) and Pityogenes chalcographus (L.). In these species, partial mortality of larvae was probably caused by the lowered quality of phloem. A significant mortality of Cryphalus abietis (Ratz.) was noted on branches.