Abstract:
Hazelnut (Corylus avellana L.) which is intensively grown in the Black Sea region is the most important agricultural product of Turkey. Hazelnut production and quality are negatively affected by several diseases and pests. Powdery mildew is nowadays one of the most common diseases in almost whole hazelnut producing areas. The disease is caused by two different species, Phyllactinia guttata (Wallr. et Lev.) Fr. and Erysiphe corylacearum U. Braun & S. Takam. For the last 4 years, E. corylacearum, a newly invasive fungus in Turkey, has been caused significant economic losses. In the present study, the efficacy of ammonium, potassium and sodium bicarbonates, and two fungicides were evaluated in field trials against powdery mildew on hazelnuts in Samsun in 2016. The application rates of compounds used in the experiment were as follows: ammonium, potassium and sodium bicarbonates (Sigma-Aldrich, Seelze, Germany) at 1.5, 3, 4.5 and 6% (w/v); CollisA (R) SC (100 g/l Kresoxim methyl +200 g/l Boscalid, BASF, Spain) at 30 ml/100 l and SulflowA (R) 80 WG (Sulphur 800 g/l, Agrofarm, Turkey) at 400 g/100 l. Of the compounds tested, except for fungicides, sodium was found to be the most effective in controlling the powdery mildew on hazelnuts, followed by potassium and ammonium, respectively. Among those three, ammonium bicarbonate was ineffective against fruit infections of the disease. There was also no significant difference between inhibitory effects of 6% sodium bicarbonate, Collis and Sulflow against the disease (P < 0.05). In addition, bicarbonate salts was phytotoxic to hazelnut leaves at concentrations greater than 1.5%. The results indicate that sodium or potassium bicarbonate solutions seems to be a useful biocompatible fungicide for controlling the powdery mildew on hazelnuts.