Laboratory and field evaluations of propolis as a plant protective agent : a thesis submitted in partial fulfilment of the requirement for the degree of Master of Horticultural Science at Massey University
Propolis is a plant derived resinous substance with known antibiotic properties. Laboratory and field trials were carried out in 1989/90 to evaluate propolis for control of insects and diseases in horticultural systems. Field trials were carried out in the organic block of Levin Horticultural Research Station. Ether extracts of propolis in agar (10, 100 1 000 and 10 000 ppm) were screened against 20 plant pathogenic fungi. Radial mycelial growth from fungal plugs were measured daily. Propolis inhibited the growth of all fungi tested although the sensitivity of fungi to propolis varied. The EC50 was between 100 and 10 000 ppm for all species with complete inhibition at 10 000 ppm in 16 species. Propolis collected from different geographic locations had different activity. There was less antifungal activity in water extracts than in ether extracts of propolis. Ethanol, surfactant and ethanol extracts of propolis were sprayed on cucumber plants weekly in a glasshouse. Weekly estimates of powdery mildew cover (Erysiphe cichoracearum) for 5 weeks were analysed. Foliar spray applications of 1% propolis extract reduced powdery mildew cover from 84.5% in the untreated plants to 33.4% in the treated ones. Eight treatments were tested on a 10 day spray calendar on zuccinis. Assessment for powdery mildew cover was made on four occassions. The number of harvested fruit from each plant were recorded. A 1% ethanol extract of propolis reduced powdery mildew only until the second assessment, 39% vs. 60% cover in the controls. The fruit number was not affected by treatments. Late blight of tomatoes (Phytophthora infestans) in the field was not affected by foliar sprays of 1% propolis extract. Radish seeds treated with a seed dressing of 36% propolis extract were not protected against (Pythium ultimum) in agar petri plate trials Laboratory screening of propolis against light brown apple moth (Epiphyas postvittana) and green peach aphid (Myzus persicae) did not indicate sufficient activity to be used in crop protection. In conclusion propolis showed some antifungal activity in laboratory trials. Successful applications in the field using the methods evaluated here however would require concentrations of raw propolis that are both impractical and uneconomic. The potential for use of propolis in plant protection is likely to come from further chemical analysis, with identification of active components and their possible synthesis. Key words: propolis, fungicide, insecticide, Phytophthora infestans, late blight of tomatoes, Erysiphe cichoracearum, powdery mildew of cucurbits, Pythium ultimum, damping off, light brown apple moth (Epiphyas postvittana), green peach aphid (Myzus persicae).