Effectiveness of lime sulphur and other inorganic fungicides against pear scab as affected by rainfall and timing application

• Published in: Journal of plant diseases and protection (2006) Vol. 124; no. 4; pp. 383 - 391
• Main Authors: Jamar, Laurent, Song, Janghoon, Fauche, Frédéric, Choi, Jangjeon, Lateur, Marc
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer 01.08.2017; Springer Berlin Heidelberg
• Subjects: Biomedical and Life Sciences; Life Sciences; Original Article; Plant Pathology; Plant Physiology; Plant Sciences; Curative fungicide; Rainfastness; Lime sulphur; Organic farming; Potassium bicarbonate; Pear scab
• ISSN: 1861-3829; 1861-3837
• DOI: 10.1007/s41348-017-0085-9

Pear scab, caused by Venturia pirina, is the most significant pear disease, causing economic losses in many pear production areas. In organic pear growing, scab control is based on the protective use of copper, or sometimes wettable sulphur. As the use of copper is subject to European restrictions and wettable sulphur has some phytotoxic effects on the main cultivated cultivars, new control strategies are needed. The aim of this study was to determine, under controlled conditions, the preventive and curative action and the rainfastness of such new fungicide formulations available for organic pear farming. The study shows that protective applications, at 300 degree-hours (DH) before inoculation, of copper hydroxide (0.1%), wettable sulphur (1%), lime sulphur (2%) and potassium bicarbonate (1%) significantly reduced pear scab severity with more than 96% effectiveness. On susceptible cultivars, under high scab pressure, lime sulphur, wettable sulphur and potassium bicarbonate are still effective for pear scab control until 300 DH after inoculation. From 300 to 650 DH after inoculation, effectiveness decreases gradually for all formulations, but lime sulphur still remains the most effective. However, with two successive applications, at 300 and 650 DH after inoculation, the second application did not provide a significant increase in protection. In addition, lime sulphur revealed a high resistance to rain compared to copper, wettable sulphur and bicarbonates, providing effective scab control and rainfastness after a simulation of 30 mm of rain. At the doses tested, no phytotoxic effect was visible for any of the compounds. Phytotoxic effect appears with wettable sulphur and potassium bicarbonate used at 2%. The potential and limitations of protection strategies against pear scab in organic farming are discussed.