The influence of temperature on in vitro toxicity of fungicides to Dydimella applanata

The production of raspberries is significantly affected by spur blight, caused by a phytopathogenic fungus Dydimella applanata (anamorph Phoma argillacea). Current disease management strategy relies on an integrated approach involving removal and destruction of all old fruited floricanes after harvest, elimination of the first flush of young canes and several applications of fungicides, starting from the middle of April until the middle of August. Temperature that differs significantly over that period may influence toxicity of fungicides and, consequently, the effectiveness of the disease control. Many papers reported the effects of different temperatures on environmental toxicity of pesticides, or insecticide toxicity to insects. On the other side, there is almost no data available on the toxicity of fungicides to phytopathogenic fungi. Therefore, the aim of this study was to evaluate in vitro toxicity of several fungicides with different modes of action to D. applanata isolates at three different temperatures suitable for D applanata development. The effect of 11 fungicides including: copper hydroxide, mancozeb, captan, chlorothalonil, dithianon, fluopyram, boscalid, pyraclostrobin fluazinam, difenoconazole, and tebuconazole on the growth of two D. applanata isolates at 15 C, 22 C, and 26 C was tested in radial growth experiments, in vitro toxicity of the fungicides was evaluated based on their concentrations in the medium that inhibited mycelial growth by 50 % (EC-50 values) compared to the fungicide-free control medium. The results showed that toxicity of fungicides was significantly affected by temperature. At 15 C all fungicides, except copper hydroxide, were most toxic to both isolates, while, at the highest tested temperature (26 C), they were least toxic. However, because of the limited number of isolates in the present study, further research is needed to determine if an increase in temperature leads to decreased toxicity of fungicides to D. applanata.