Effects of seed coatings with thiamethoxam on germination and flea beetle control in flax.

Flea beetles damage the seedlings before and after emergence and later the top of the plants as well, resulting in forking of the stem. This is unacceptable for the flax fibre industry, since it influences fibre quality negatively. Five field trials were carried out in 2001, 2003 and 2004 to assess the control of the flax flea beetles Longitarsus parvulus (Payk) and the large flax flea beetle Aphthona euphorbiae (Schrank) by film coating the seeds with thiamethoxam in fibre flax crops (Linum usitatissimum L.). Seed treatments were compared with untreated seeds and standard post emergence sprays with deltamethrin or parathion-methyl. Film coatings of the seeds with thiamethoxam formulated as 280 g/l, 350 g/l and 600 g/l were used. Thiamethoxam 350 g/l at rates of 9.1 and 18.2 g a.i./kg seed resulted in phytotoxicity, shown by a decrease of emergence. Application of thiamethoxam 350 g/l and 600 g/l at rates of 1.1 g a.i./kg seed and higher resulted in excellent flea beetle control. Application of thiamethoxam 280 g/l at a rate of 1.1 g a.i./kg seed showed no decrease of attack in comparison with the standard spray treatment. Seed treatment with thiamethoxam 600 g/l at 0.6 g a.i./kg showed insufficient protection.