Occurrence of Cytospora sensu lato in declining apricots in Czech Republic and in vitro effectiveness of fungicides

Abstract: Apricot (Prunus armeniaca L.) represents one of the most favourite stone fruit
species for growing in the Czech Republic. Their premature dying is a significant issue for fruit growers. This problem is a complex of influences caused by a combination of biotic and abiotic factors. Among fungal pathogens contributing to apricot decline, wood-decaying fungi of the anamorphic genus Cytospora spp. are the most often concerned. Screening of apricot orchards in the Czech Republic in years 2019, 2020, and 2021 showed Cytospora leucostoma and Valsaria insitiva (syn. C. cincta) as the most frequent pathogens causing shoot and twig
necrosis. This study investigated also the efficiency of selected commercial fungicides (14 in
total) in relation to growth of colonies of the pathogens Cytospora sensu lato using in vitro
testing methods on agar plates with addition of fungicide. Fungicides contained following
active substances: trifloxystrobin, fluopyram, tebuconazol, fenpyrazamin, myclobutanil,
fenhexamid, mancozeb, boscalid, pyraclostrobin, fosetyl-Al, dithianon, pyrimethanil and
difenoconazol. Luna Experience and Horizon 250 EW containing tebuconazol and Score 250
EC containing difenoconazol were the most effective identified fungicides. Other effective
fungicides Talent and Dithane DG Neotec containing myclobutanil and mancozeb resp. are no longer registered for use in the Czech Republic.