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Abstract
Introduction
The pine bark bug Aradus cinnamomeus Panzer (Heteroptera, Aradidae) inhabits forest plantations of Scots pine (Pinus sylvestris L.) at the age of 5 years, which leads to deterioration of their health and growth. In the North-East of Ukraine in recent years the population of this species has increased in connection with increasing areas of pine crops.
The results of the studies conducted in other regions show that the reduction of harm caused by the pine bark bug can be provided by forestry activities aimed at the formation of favorable environmental conditions for increasing resistance of pine stands. The establishment of mixed plantations and the application of mineral substances usually enhance the pine resilience. However, the information on the impact of mineral and biological elements to reduce the number of pests is still scanty.
The aim of our study was to determine the effectiveness of soil application of mineral and biological substances to reduce the number of pine bark bug and increase the sustainability of pine plantations.
Materials and methods
The study was performed in planted pine stand in Seredino-Budskiy agroforestry (Seredino-Budskiy district, Sumy region) in the subcompartment 34 of compartment 7. The plot area was 1.1 ha. The pure (100 % of Scots pine) plantation was established on former agricultural lands in 1998. The terrain is flat. The type of forest site conditions is fresh infertile pine site. The forest type is a fresh pine forest. The soil is sod-cryptopodzolic argillo-arenaceous one on fluvio-glacial sands. On the north-eastern side of the plot, there is Scots pine plantation established in 1992, which is mixed in composition (80 % Scots pine, 20 5 silver birch). On the south side, there are private lands. The tillage was conducted in the autumn of 1997 with the use of the PKL-70 plow with the creation of grooves 0.25 m deep. The plantation was established in the spring of 1998 by hand. The number of planting sites was 5,714 trees per ha with 2.5 ? 0.7 m planting pattern. To create the plantation, the planting material of Scots pine of the first year of cultivation and of the first quality class was used. The survival rate of the seedlings was 81 % in the first year. At the time of the experiment (2012), the conservation of the plantation was 64 %.
The experiments were conducted in the south-western part of the subcompartment in the area of 50 ? 100 m (0.5 ha) in 12 variants with 50 trees in each variant. Mineral substances were added to an aqueous solution. With this purpose, we used ammonium nitrate (200 g per tree), potash (150 g per tree) phosphorus fertilizer (200 g per tree) and an aqueous solution of detergent (surfactant 50 l per tree). As biological substances, the crushed leaf litter of deciduous trees (silver birch (Betula pendula Roth), small-leaved lime (Tilia cordata Mill.), English oak (Quercus robur L.), common hazel Corylus avellana L., and red elder (Sambucus racemosa L.)) and ash elements (post-fire residues) were used. In some variants, we aplied pure water (200 l per tree). Separately for each experiment, the variant without any compounds (the control) was laid out.
The litter of deciduous species was crushed using “Elikor 1” chopper. The crushed litter was placed under the trees in a radius of 50 cm in an amount of 5 kg under the same tree with the subsequent digging of the soil with a shovel. Ash elements were added in an aqueous solution in an amount of 200 g per tree.
Mineral and organic substances were placed annually in 2011-2014. We evaluated the effectiveness of the activities in 2012-2014 according to the density of the pest, health of the trees and their growth.
Results and Conclusions
In the variants, where mineral substances were applied for four years, the population density of pine bark bug decreased by 76.9 % (nitrogen), 49.3 % (potassium), 48,4 % (phosphate fertilizers), and 89.5 % (ash). The positive impact of ash, reducing the density of the pest, was noticeable already in 2012, of nitrogen fertilizers in 2013, while of phosphate and potash in 2014.
In the variants, where the crushed leaves of tree and shrub species (5 kg per tree) were added for four years, a rapid reduction of population density of pine bark bugs was identified after the introduction of the litter of silver birch. In general, during four years of the study, the population density of pine bark bug reduced by 54.1 % in application of silver birch litter, by 33.3 % English oak, by 26.8 % small-leaved linden. The least effect was in the case of use of the litter of red elder (22.8 %) and common hazel (19.3 %).
We calculated the technical efficiency of application of mineral and organic substances taking into account the changes in pest population density in the control. The calculations support the conclusion about the highest efficiency of application of ash (92.2 %), ammonium nitrate (82.8 %) and relatively high effectiveness of the application of leaf litter of silver birch (65.9 %), potash (62.3 %) and phosphorus fertilizers (61.6 %). The health of the stand has improved in the variant of nitrogen (decrease of health condition indices IcI–V and IcI–IV by 9.9 and 12.3 % respectively) and ash (decrease of health condition indices IcI–V and IcI–IV by 2.9 and 3.2 % respectively). In the variant of birch leaf litter, the health of stand has not changed, and the variant of oak litter applying the health condition has deteriorated (the increase of the health condition indices IcI–V and IcI–IV by 14.0 and 6.3 % respectively).
Thus, the highest efficiency was obtained in the variants with applying mineral fertilizers and ash. Somewhat less effective was the use of the leaf litter of silver birch. The study has shown that the presence of silver birch in a stand composition contributes to reducing the probability of pine trees colonization by pine bark bug in conditions of the fresh coniferous forest.
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