The Effect of Different Forms of Sulphur on Incidence of Apple Scab on Apple Tree (Malus x domestica Borkh) Gloster CV.

From 2014 to 2015 the influence of foliar application of sulphur on apple trees (Gloster cv.)was investigated in the apple orchard at the Research and Breeding Institute of Pomology in Holovousy (North-East Bohemia, Czech Republic). The experiment was based on foliar applications of fertilizers containing different forms of sulphur: elemental S⁰, sulphate SO₄²⁻ and thiosulphate S₂O₃²⁻ (in combination with other macro- and microelements) and fungicides with or without sulphur: Kumulus (S⁰ + F) and the conventional fungicide programme (F), in the respective treatments. Apple scab incidence on leaves and fruits was investigated in each experimental year according to the relevant methodology of the OEPP/EPPO standard PP1/5(3) Venturia inaequalis. Data on the incidence of apple scab correlate with the process of pathogen life cycle and risk of infection on the given dates. The incidence of apple scab was the lowest in 2014 in treatment S⁰ + F (10.8 % on leaves, 2.8 % on fruits) and F (15.8 % on leaves, 6 % on fruits) where conventional fungicides were used. When compared with the other treatments these treatments were the most effective even if the incidence of scab in the individual treatments in 2015 increased by 28 to 60 % due to high infection pressure. The results confirmed the efficiency of the conventional fungicide programme (S⁰ + F and F) against apple scab incidence on fruits. What is more, the results were slightly better in the treatment, where the conventional fungicide programme was combined with fertilizer containing elemental S (S⁰ + F) in comparison with fungicides applied alone (F). The effect of the other forms of sulphur (SO₄ and S₂O₃) on apple scab control has not been confirmed. According to the results, the application of the conventional fungicide programme (S⁰ + F and F) is more effective against scab incidence than the inorganic forms of sulphur alone.