Bitter pit is a physiological disorder that significantly reduces the quality of apples. Although it has been detected since the beginning of the last century, still there is little known about the mechanism of its occurrence. According to numerous studies, bitter pit is formed as a result of calcium deficiency in the fruit. Some authors cite the high concentration of gibberellins, later in the production season, most probably caused by excessive activity of the roots, as the chief causative factor. Beside Ca, there are several factors that can also contribute to its development, like imbalance among some mineral elements (N, P, K and Mg), cultivar, rootstock, the ratio of vegetative and generative growth, post-harvest treatments and the storage methods. There are some prediction models available that can estimate the risk of bitter pit in apples, but even those are not always reliable. The aim of this review was to encompass the pre and postharvest factors which cause bitter pit and point out the directions for solving this problem.

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Four anti-hail and anti-insect nets (red, white and yellow anti-hail and Stop Drosophila Normal) were used on apple cv. 'Braeburn' grown in northern Croatia in order to evaluate their effect on fruit colouration that was measured with the colorimeter (expressed as: L* -lightness, a* -yellow/blue b* -green/red) on two sides of fruit ("green" side and "red" side), and also they were used in order to evaluate their effect on the coloured surface percentage, apart from their anti-hail and pest damage protection properties. The fruits were harvested on 12 th October 2015. Most differences were found between the fruit grown under the white anti-hail net and the fruit grown without the anti-hail net. Colour value "a*" was lower on the red side of the fruit under the white net in comparison with the red net. On the green side,"a*" value was lower and "L*" value was higher under the white net in comparison with control fruit. Different net colour had no influence on total colour difference. Regarding to the colouration, differences among the nets are found in classes 0-25% and 50-75% of skin coloured fruit. The fruit grown under the white nets had the higher percentage of fruit in class 0-25% than those grown without the net. The lower share of fruit in class 50-75% of skin colouration was recorded under the white net than under the red net or in the control fruit. Colouration index was lower in the fruit grown under the white net than in the control fruit. It can be concluded that the white anti-hail net promotes ripening, but at the same time it decreases red colouration. No significant differences in fruit colour have been found in the fruit grown under the red, yellow and Stop Drosophila Normal nets. Some accepted colour parameters such as a*/b* ratio are not appropriate for describing colour changes in 'Braeburn' apple in this study.

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Abstract. Ground beetles (fam. Carabidae) as beneficial insects are valuable organisms to study whether any of the new implemented agricultural measures in fruit production is beneficial. The aim of our study was to analyze impact of different types of exclusion nets on ground beetle species composition and abundance in an apple orchard. The study was conducted in an IPM apple orchard, situated in the northwest part of Croatia. The treatments for the study were four types of exclusion (colored) nets (Agritenax white, Agritenax yellow and Agritenax red all with photo selective properties and Stop Drosophila Normal net -pearl color) and non-covered trees acted as a control. Ground beetles were collected during the summer and autumn (from July 1 st until October 15 th in 2015) with pitfall traps. During the study, a total of 1559 specimens of ground beetles were identified and sorted into 28 species. Significant differences in the captures under nets were observed for species: Anchomenus (Anchomenus) dorsalis (Pontoppidan 1763), Microlestes minutulus (Goeze 1777), and Pterostichus (Feronidius) melas melas (Creutzer 1799). The most of the ground beetles (413) were recorded under the Agritenax yellow nets and the least (184) in the control. Our study showed the positive effect of exclusion nets on ground beetle species composition and diversity in IPM apple orchard thus confirming their value in assessing the introduction of new agricultural measures into practice.