Insecticidal effects of insecticide, fungicide, complex fertilizer and wetting agent combinations depending on water hardness

Simultaneous occurrence of different harmful species in agricultural practice necessitates that different plant protection chemicals be applied at the same time (tank mix). Mix components differ in purpose, mode of action and/or formulation, while addition of no pesticide components (complex fertilizers, adjuvant and wetting agents) is widely practiced today. However, data concerning the effects of water quality used for preparation of working liquids on the biological effects of pesticides is still scarce. Therefore, the objective of this study was to determine insecticidal effects as depending on components used in mixes and water hardness. The effects of mixtures of thiametoxam (Actara 25-WG 0,07kg/ha) with azoxystrobin (Quadris 0.75 l/ha), mancozeb (Dithane M-70 2.5 kg/ha), a complex fertilizer (Mortonijc plus 3 kg/ha) and a wetting agent (Silwet L-77), depending on the components and water hardness (slightly hard (15.4 d?) - tap water from Novi Sad, and very hard (34.7 d?) - well water from Adica, a Novi Sad suburb), were determined in a bioassay based on adult mortality rate of the first generation of Colorado potato beetle (Leptinotarsa decemlineata Say). The mixtures were applied by a flooding method. The trial was set up to include four replications. Insecticidal effects were determined 24 h and 48 h after exposure. Thiametoxam effectiveness 24 h and 48 h after application in slightly hard water was 100% when the insecticide was applied alone and in double and triple mixes with the fungicides, complex fertilizer and wetting agent, showing no dependency on mix components. The tested adult population of Colorado potato beetle demonstrated high susceptibility to thiametoxam, while the other components had no impact in slightly hard water. In very hard water, 24 h after application, the insecticidal effect had the same level of significance to thiametoxam in double and triple mixes, with an exception of thiametoxam+mancozeb+Mortonijc plus and thiametoxam+mancozeb+wetting agent combinations, which showed significantly lower efficacy. After 48 h, substantially lower effectiveness, in comparison with the sole insecticide and other combinations, was only observed in thiametoksam+mancozeb+Mortonjic plus combination. Significantly lower efficacy of that combination is probably due to an incompatibility of the macozeb preparation and the complex fertilizer containing boron (B), which was evidenced only in very hard water.