A during-infection spray strategy using sulphur compounds,copper, silicon and a new formulation of potassium bicarbonate for primary scab control in organic apple production |
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Authors: | L Jamar B Lefrancq C Fassotte M Lateur |
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Institution: | (1) Département Lutte biologique et Ressources phytogénétiques, Centre wallon de Recherches agronomiques, rue de Liroux 4, 5030 Gembloux, Belgium |
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Abstract: | In a field experiment conducted over two growing seasons, the effectiveness and phytotoxicity of inorganic fungicides such
as sulphur, lime sulphur, copper, silicon and Armicarb (a new formulation of potassium bicarbonate) was compared with water
for the control of primary apple scab infections in Belgium on high, medium and low scab-susceptible cultivars (cvs ‘Pinova’,
‘Pirouette’ and ‘Reinette des Capucins’, respectively). In order to drastically reduce the amount of fungicide applied in
the orchard, two approaches were used: (1) a strategy involving spraying during the infection process, before fungal penetration
and (2) a tunnel sprayer machine for treatment applications. Under field conditions highly favourable for disease, low rates
of elemental sulphur (31.8 and 38.6 kg ha−1 year−1 in 2005 and 2006, respectively) combined with low rates of copper (2.1 kg ha−1 year−1 in both years) provided the best scab control and reduced scab severity on the fruits of cv. ‘Pinova’ by 97 and 98% compared
with water control in 2005 and 2006, respectively. Lime sulphur was much more effective than wettable sulphur and appeared
to be efficient at temperatures below 10°C, but its effectiveness against apple scab decreased if the treatments were applied
12–24 h later than in the ‘during-infection’ spray strategy. Armicarb used alone significantly reduced apple scab severity
on the leaves and fruits of the three cultivars compared with the water control. Its effectiveness was as good as wettable
sulphur applied using the same timing and dosage. Silicon reduced apple scab on fruits very slightly, but not on leaves. The
amounts of wettable sulphur, lime sulphur, copper, silicon and potassium bicarbonate used in this experiment to control apple
scab were not phytotoxic, did not increase fruit russet, did increase the yield of each cultivar and did not affect summer
density of the beneficial Typhlodromus pyri. The potential and limitations of ‘during-infection’ spraying as a protection strategy against apple scab in organic farming
are discussed. |
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Keywords: | Alternative control Disease management Lime sulphur Natural substances Polygenic resistance Typhlodromus pyri Venturia inaequalis |
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