Slaked lime against european fruit tree canker: efficacy and introduction into practice

Summary

European fruit tree canker, caused by Nectria galligena, is a major disease in organic apple cultivation. No copper can be used in Denmark and the Netherlands to control the disease. Removal of cankers is the only remaining method to control the disease. Slaked lime (calcium hydroxide) was applied at 50 or 100 kg/ha three times during the leaf fall period to protect apple trees against the disease. Experiments under high inoculum pressure showed a reduction in newly formed cankers of 57, 35 and 60 % with respect to untreated for 3 years respectively. The chemical standard thiophanate-methyl further reduced the number of newly formed cankers by 99, 60 and 89 % with respect to untreated for these 3 years respectively in these experiments. These results showed that slaked lime was less efficacious than the chemical standard under these high inoculum pressure circumstances. Demonstration experiments showed an efficacy of 70 and 68 % for slaked lime and 62 and 62 % for the conventional standard (carbendazim and captan) with respect to untreated controls in 2 years respectively. The demonstration experiments, done in commercial orchards and under normal inoculum pressure, showed a similar efficacy as the conventional standard. It is concluded that the use of slaked lime to control European fruit tree canker can contribute to a more economic organic apple and pear production in temperate climate zones.