Studies on the control of Erysiphe corylacearum, the destructive powdery mildew disease in hazelnut, with some environmentally friendly products

This study was conducted under greenhouse and laboratory conditions to determine the efficacy of environmentally friendly products known for their use in plant disease management against powdery mildew caused by Erysiphe corylacearum in hazelnut. The tested products included thyme essential oil, a commercial product containing laminarin (Laminar), a commercial product containing Bacillus subtilis (Serenade), a chitosan-based formulation (Chitligsan), and milk (Pınar). To enable a comparison with these products, Collis SC, a conventional fungicide registered for use against the disease in our country, was included in the study. The treatments were conducted under two different programs: Program A, which began with a protective application before artificial inoculation, and Program B, where the first applications were made after the appearance of initial symptoms following artificial inoculation. In the laboratory study, the inhibition rates of conidial germination at different doses of the products were evaluated on leaf discs, and the effective concentrations (EC50) required to inhibit conidial germination by 50% were calculated. On the first evaluation date, Collis demonstrated an efficacy rate of 97.82% in Program A, followed by laminarin (59.96%) and thyme essential oil (59.94%), with no statistically significant difference between the latter two. B. subtilis (53.85%), milk (41.83%), and chitosan (32.31%) showed statistically different efficacy from Collis but belonged to the same statistical group among themselves. In Program B, Collis exhibited the highest efficacy (90.94%), followed by Bacillus subtilis (70.24%) and chitosan (52.66%). On the second evaluation date in Program A, all treatments, except for chitosan, which had the lowest efficacy (43.33%), were not found to be statistically different from Collis, which had the highest efficacy (97.61%). In Program B, chitosan (76.88%) and Bacillus subtilis (74.52%) were in the same efficacy group as Collis (77.62%). In terms of efficacy, Program A and Program B showed a difference only in the milk treatment on the second evaluation date (66.28% and 19.68%, respectively), while similar results were obtained for the other treatments. In the laboratory study, thyme essential oil inhibited conidial germination by 83.41% to 92.01%, chitosan by 39.00% to 68.27%, milk by 32.51% to 72.62%, Bacillus subtilis by 75.99% to 88.89%, and laminarin by 40.01% to 69.64% at different doses. As the doses of the products increased, the inhibition of conidial germination also increased. The EC50 values of the products were determined as follows: 0.02 µL/mL for thyme essential oil, 0.22 mL/mL for chitosan, 0.07 mL/mL for milk, 0.001 mL/mL for Bacillus subtilis, and 0.43 µL/mL for laminarin.