Application of biostimulators in the growth and protection of pedunculate oak (Quercus robur L.) seedlings in bare-root nursery

Pedunculate oak is a species of major economic importance in Polish forests. This species seedlings constitute 18.9% of the nursery production in the country. One of the most widespread fungal disease these oaks face is the oak powdery mildew induced by Erysiphe alphitoides. Nursery production is on the lookout for environment-friendly means of plant protection as well as growth simulators capable of raising levels of productivity. Our objectives was to assess two preparation treatments regarded as biostimulators (registered as fertilisers under the names Apol-Humus and Apol-Hum Chelat) in the raising of seedlings of pedunculate oak in bare-root nursery conditions. The experiment included 6 variants with seedlings treated with the above agents, protected against mildew in the traditional way using Falcon 460 EC, treated with fertiliser and fungicide at the same time, or left as control specimens with no measures taken. All preparations were applied by means of foliar spraying 5 times in the course of the season. Survival of seedlings was then assessed at the season end, along with biometric features like root-collar diameter, length of main root and stem, dry mass of leaves and stem, and degree of oak powdery mildew attack. Results indicated curtailment of mildew infection of oak seedlings thanks to both of the biostimulators, albeit to a more limited extent than when fungicide was applied. No stimulation of seedling growth was achieved, however, though the most favourable biometric parameters characterised the oaks supplied with both biostimulator and fungicide. Significantly higher survival rate was noted for oaks offered effective protection against mildew, in the variants with the fungicide or with simultaneous application of Apol-Humus or Apol-Hum Chelat with Falcon. The research points to the two biostimulators under study (based on natural components) being suitable for use in the nursery production of pedunculate oak seedlings, with it being presumed that either or both can allow for reduction in amount of fungicide necessary to be used to safeguard seedlings against mildew.