Simultaneous occurrence of different harmful agents in agriculture necessitates a combined application of chemicals differing in purpose, action and/or formulation. Complex fertilizers may be a component of these combinations. There are scant literature data on biological effects of such combinations and their response to the quality of water added to them. Effects of the mixture (cypermethrin, azoxystrobin, mancozeb, a complex fertilizer Mortonijc plus /M+/, wetting agent), depending on components and water quality (slightly hard and very hard), was determined in a biotest. The mixtures were applied by the flooding method. Insecticide effect was determined on the basis of mortality Colorado potato beetle (Leptinotarsa decemlineata Say.) rates 24 and 48 h after treatment. The effectiveness of cypermethrin applied with a slightly hard water was 86%, 24 h after treatment. However, the triple combination cypermethrin+azoxystrobin+M+ exhibited a significantly higher effectiveness compared with the double combination cypermethrin+azoxystrobin. The combination cypermethrin+mancozeb+wetting agent exhibited a similar significant effectiveness (96%) compared with the double combination cypermethrin+mancozeb. Therefore, when added to a slightly hard water, the insecticide alone showed no change in effectiveness, however, differences existed among the mixtures. Forty-eight hours after treatment, insect recovery and reduction in effectiveness (68-75%) became evident, especially in the double combinations with fungicides. The effectiveness of the double combinations was significantly increased (to 89-98%) by adding a fertilizer or a wetting agent. After 24 h, the effectiveness of cypermethrin added to a very hard water was 78% in the case of the combinations and 80-95%. In relation to the application of the insecticide, a significant increase in effectiveness was achieved only with the mixture cypermethrin+azoxystrobin+M+. The effectiveness of cypermethrin and the mixtures was reduced 48 h after treatment. Still, when added to a very hard water, all mixtures were significantly more effective than the insecticide alone.
