Physical properties and toxicity of thiamethoxam tank mix with some fungicides

Abstract

The intensive protection of potato in practice is very often accomplished through joint application of insecticides and fungicides against foliar pathogens. The tank mixe partners ought to be carefully chosen, considering formulation and water quality, in order to avoiding activity decrease or phytotoxicity. The physical properties (emulsion/suspension stability, surface tension/wettability and acidity - alkalinity values) of product Actara 25-WG (thiamethoxam) and its tank mixes were dependent on mixture partners - fungicides Mankogal-80 (mankozeb), Polyram-DF (metiram), Ridomil MZ-72 WP (metalaxyl+mankozeb) and Folpan WP-50 (folpet) and water quality. Three types of water were used: a) standard hard water (SHW), with surface tension 60 din/cm, b) deteriorated tap water from N. Sad, supplied as raw water to S. Karlovci (SKW), with surface tension 70 din/cm and c) technical water from shallow well from agriculture estate in Lukicevo (LW), with surface tension 62 din/cm. The surface tensions of Folpan WP-50 suspension in SKW and LW were the lowest of all fungicides, immediately and after 24 h 0/24 equal - 37/36 and 36/35 din/cm in SKW and LW, respectively. The tank mix suspensions of Actara 25-WG with Folpan WP-50 had similar surface tension (34/34 and 37/37 din/cm) in SKW and LW, respectively. The tank mix of insecticide and fungicide Mankogal-80 exhibited reduced stability regardless of the water quality. The pH of suspensions increased by 24 h ageing, except for Folpan WP-50 and the tank mix Actara 25-WG and Folpan WP-50 in SHW, where the pH decreased by ageing. The high initial effect on overwintered adults of Colorado Potato Beetle (CPB) was observed with either Actara 25-WG alone, or its mixtures with fungicides. However, the rate in mortality during 5 days of observation was different depending on fungicide partner in the tank mix. Five days after treatment no significant differences between Actara 25-WG and Actara 25-WG tank mixed with fungicides were detectable.