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Reviews records of the occurrence of terminal dieback in P. sylvestris in Norway from 1863, and describes the symptoms and distribution of damage occurring in 1963. Sample trees ca. 0.5-2.0 m. high from 50 localities in which damage had occurred, and meteorological records for these areas, were studied. In view of the apparent connexion with summer frosts, special attention was paid to the development of annual rings and the occurrence of frost rings in the late wood. Results indicated that for every summer in which damage occurred there had been a short growing season with very low mean temperatures, and this had generally been preceded by a favourable summer in the previous year. These conditions appear to lead to insufficient development of the shoots, which do not acquire their normal frost hardiness. Such predisposed shoots may be injured by frost during the following dormant period or, as probably happened in 1963, by unfavourable early spring weather.


In a further study to assist in estimating the profitability of insect control measures [cf. F.A. 30 No. 6021], 2-year-old Pinus patula plants were artificially defoliated in the rainy and the dry seasons at localities in Kenya, Uganda and Tanzania. Complete defoliation caused a reduction in height and diameter growth of ca. 50% for the year in question. With a few exceptions, ca. 50% defoliation, removing either (a) the youngest, or (b) the oldest foliage, did not significantly reduce growth, nor were there significant differences between (a) and (b). Trees defoliated at the start of the dry season recovered more slowly and showed a greater loss of growth than those defoliated at the end of the dry, or during the rainy season. Growth reduction by short-term 50% defoliation would seem to be economically tolerable, in that measures to prevent it would be uneconomic.