Evaluation of chemical disinfestants in reducing Verticillium dahliae conidia in irrigation water

Irrigation water disinfestation is an unexplored option for reducing Verticillium dahliae inoculum in water and consequently for more efficiently managing Verticillium wilts in Andalusia. We assessed Suppressive Efficacy (SE; water was infested and subsequently treated) and Preventive Efficacy (PE; previously treated water was subsequently inoculated) of OX-VIRIN®, OX-AGUA AL 25® and Deccoklor® in reducing water infestations by V. dahliae conidia. Five concentrations of each disinfestant, the lowest three being recommended by the manufacturer, were tested in vitro against six V. dahliae isolates. Validation assays were carried out in experiments under natural environmental conditions in spring. The four highest concentrations of OX-VIRIN® (0.8–51.2 mL L−1), the three highest of OX-AGUA AL 25® (46.4–417.5 μL L−1) and the two highest of Deccoklor® (0.375 and 3.75 mL L−1), showed an in vitro-efficacy (SE and PE) of 96.2, 80.0 and 100.0% after 30, 5 to 30 and 15 days respectively. Therefore, recommended concentrations for OX-VIRIN® and OX-AGUA AL 25® showed a greater in vitro-effectiveness than those recommended for Deccoklor®. Assays in natural environmental conditions proved that OX-VIRIN® at the recommended concentration of 3.2-mL L−1, applied every 28 days to water, was the most effective treatment (SE and PE), with a 100% reduction of the average relative viability after 56 days. Other chemical treatments showing high in vitro-efficacy, such as OX-VIRIN® at 0.8 mL L−1 and OX-AGUA AL 25® at 46.4 μL L−1 showed an SE of 99.9% after 14 and 28 days when applied every 28 and 14 days, respectively. However, PE of OX-AGUA AL 25® at 46.4 μL L−1 was only 59 and 38% after 28 and 14 days respectively, depending on the experiment.