Abstract
The control of apple scab and powdery mildew is a challenge for organic fruit growing. Bicarbonate salts are already consecrate in reducing the attack of scab and powdery mildew in organic apple culture. In the current study the influence of some products accepted in organic apple production to control scab and powdery mildew (potasium bicarbonate, lime sulphur, wettable sulphur, potassium silicate, cooper ammonium-phosphate, potassium bicarbonate + potassium silicate, potassium bicarbonate + wettable sulphur) in comparison with untreated control, were used. The biological material was represented by three scab resistant cultivars (‘Luna’, ‘Topaz’ and ‘Sirius’) and three scab susceptible cultivars (‘Elstar’, ‘Pinova’ and ‘Golden Delicious’). The experiments were carried out during 2014-2016 at Steluța LTD, Cluj-Napoca, N.W. Romania, as a bifactorial experiment arranged in randomized blocks. The trees were planted in 2011 at a density of 3,175 trees/ha. Depending of the year, a number of 18-22 treatments were made annually after each rain. It can be concluded that the combination of potassium bicarbonate + wettable sulphur significantly reduced the attack degree of scab and powdery mildew on leaves and fruits and increased the yield of the scab-susceptible and scab resistant cultivars. Good results were obtained in the case of treatment with potassium bicarbonate with potassium silicate, potassium bicarbonate and cooper ammonium phosphate. The treatments with the products used in the experiments did not register symptoms of phytotoxicity on leaves or fruits, except lime sulphur and wettable sulphur and cooper ammonium phosphates.
Highlights
In the last decades, organic apple crop is constantly expanding, and the demand for healthy apples, with no chemical residual products, is increasing
Most commercial apple grown cultivars are very sensitive to scab, so that in an commercial apple orchard, very frequent fungicide applications (15-22 annually) are applied in order to control apple scab, depending on weather conditions, disease pressure and cultivar susceptibility (Holb et al, 2005)
The trees have not been maintained according to organic production standards, excepting the control of scab and powdery mildew
Summary
Organic apple crop is constantly expanding, and the demand for healthy apples, with no chemical residual products, is increasing. Just a few approved chemical products are available for disease control, mainly based on sulphur and copper (Holb, 2008); various natural plant extracts containing triterpenoid saponins, polyphenols and specific flavonoids have been reported to have antifungal properties (Köhl et al, 2007; Bahraminejad et al, 2008; Bengstsson et al, 2009; Jamar et al, 2010). Another way to control these diseases could be the cultivation of low scab-susceptible or scab-resistant cultivars having the Vf gene.
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