‘Bordeaux’/‘Kumulus’ Regimes and ‘Surround’ in Organic Apple Production in New Brunswick: Impacts on Apple Scab, Fruit Russeting and Leaf Gas Exchange

Privé, J.-P.¹, Braun, G.², Russell, L.¹, and LeBlanc, A.¹

A field trial was conducted over 2 growing seasons in a ‘Ginger Gold’ apple orchard in Bouctouche, New Brunswick, Canada to assess the efficacy of different regimes of 2 organic fungicides, ‘Bordeaux’ (Copper 53W at 2 kg/ha + hydrated lime at 10 kg/ha) and ‘Kumulus’ (80% sulphur at 22.5 kg/ha), in controlling apple scab (Venturia inaequalis) and preventing fruit russeting. ‘Surround’ (95% kaolin clay at 50 kg/ha), an organic crop protectant, was used for insect control; its impact on leaf gas exchange [net photosynthesis (Pn), stomatal conductance (gs), intercellular CO2 (ci) and transpiration (E)] was evaluated.

A very minor incidence of fruit damage due to scab coupled with a high occurrence of fruit russeting characterized the first year of the study; the converse was observed in the following year. The fungicide treatments exacerbated the occurrence and severity of fruit russeting in the first growing season and reduced the incidence of apple scab in the second season.

The disparities in the prevalence of apple scab and fruit russeting between years can be attributed largely to a difference in the weather conditions characterizing the growing seasons. At leaf residue rates of up to 3.7 g/m2, ‘Surround’ was not found to influence leaf gas exchange; however, the interaction of ‘Surround residue x leaf temperature’ was found to affect leaf transpiration.

 

¹ Agriculture & Agri-Food Canada, Bouctouche, NB;

² Agriculture & Agri-Food Canada, Kentville, NS, Canada