The effectiveness of fungicides and warning systems in controlling Botryosphaeria dothidea in apple fruit rot in southern Brazil

Abstract: White rot causes up to 30% losses in apple orchards with frequent outbreaks in hot and humid summers. The current study reports the results of a warning system applied to white rot outbreaks, as well as the effectiveness of fungicides in controlling the disease. The epidemiological warnings were recorded in the 2002 to 2003 and 2003 to 2004 periods. During the first season, warnings were issued whenever there was inoculum available and two consecutive days of rainfall occurred, and in the second season after 5 mm of rain. In the 2016 to 2017 period, spraying was done when white rot risk warnings were predicted according to the weather forecast information. To compare fungicide effects, fungicides were sprayed on cv. Fuji apple trees before and after harvest, as well as before and/or after inoculation with Botryosphaeria dothidea. The warning system under the 5 mm of rainfall condition and the preventive treatment were equally efficient in managing the disease. Fungicides belonging to the benzimidazole group, sprayed at the pre-harvest stage, showed the most efficient disease control. The most effective products sprayed at the post-harvest stage were thiophanate-methyl, mancozeb and calcium chloride.