The influence of temperature, humidity and light on the conidial germination and germ tube elongation of oak powdery mildew (Microsphaera alphitoides Griff. et Maubl.) was studied in controlled conditions. The maximal germ tube length was attained at 25°C, whereas at lower and higher than optimal temperatures, germ tube growth was significantly lower. Germ tubes begin to develop at all values of relative humidity (10-100%), reaching the maximum length at 90%. The development of germ tubes was the most intense in full light and the lowest in total darkness. The artificial infection of floating leaves showed that an increasing age had an inhibitory effect on the mycelium development and spore formation. Since conidia play a crucial role in powdery mildew epidemiology, it is of particular importance to elucidate the influence of environmental factors in the complex relations that exist between the plant and its pathogen. [Projekat Ministarstva nauke Republike Srbije, br. 43007: Studying climate change and its influence on the environment: Impacts, adaptation and mitigation

The oak lace bug (Corythucha arcuata Say) was introduced to Europe from North America in 2000 and was first recorded in Serbia in 2013. It is a very serious oak pest which has harmful effect in both adult and nymph stages of the insect that feeds by sucking the sap on the lower (abaxial) leaf side. As this is a relatively new pest in our country, the possibility of its control by applying insecticides was tested during 2021. The paper presents the test results of three insecticidal active substances: deltamethrin, flonicamid and acetamiprid for the control of oak lace bugs. The insecticide flonicamid did not show sufficient efficacy in the suppression of the oak lace bug, while deltamethrin and acetamiprid have high efficiency for the suppression of the adults and nymphs of the oak lace bug, which recommended them for this purpose.

Oak powdery mildew (Erysiphe alphitoides (Griffon and Maubl.) U. Braun and S. Takam.)) is one of the most common foliar pathogenic organism of oaks, exploiting harmful effects, particularly on young seedlings. To assess and evaluate these negative effects, an experiment was conducted under semi-controlled conditions with 20 one-year-old seedlings of Quercus robur L. infected with E. alphitoides, half of them showing 50% of leaf coverage by epiphytic mycelia and the other half a coverage of 75%. The results of the present study have shown that all observed parameters of chlorophyll a fluorescence transient were highly effective in the detection of severe biotic stress. Moreover, the studied parameters of slow fluorescence kinetics were also considerably influenced, with the coefficient of non-photochemical fluorescence quenching and the Stem-Volmer type non-photochemical fluorescence quenching parameters showing the fastest responses. In case of leaf stomatal traits, the decrease of stomata guard cell width coupled with the increase of stomatal density was observed as the protective mechanism of Q. robur against the stressor. The overall results showed the adverse effects of powdery mildew infection on the photosynthesis of pedunculate oak seedlings, which progressed in time and depended on the severity of the infection. The importance of the results of the present study lays in evaluation and monitoring of the effects of powdery mildew development on the photosynthetic apparatus of one-year-old Q. robur seedlings, which is the most vulnerable stage for the infection by the mentioned pathogen.