Pest Management Science Pest Manag Sci 64:215–222 (2008) Influence of imidacloprid seed treatments on rice germination and early seedling growth Mark M Stevens, 1∗ Russell F Reinke, 1 Neil E Coombes, 2 Stuart Helliwell 3 and Jianhua Mo 1 1 EH Graham Centre for Agricultural Innovation (NSW Department of Primary Industries and Charles Sturt University), Yanco Agricultural Institute, Private Mail Bag, Yanco, NSW 2703, Australia 2 EH Graham Centre for Agricultural Innovation (NSW Department of Primary Industries and Charles Sturt University), Wagga Wagga Agricultural Institute, Private Mail Bag, Wagga Wagga, NSW 2650, Australia 3 School of Wine and Food Science, Charles Sturt University, Locked Bag 588, Wagga Wagga, NSW 2678, Australia Abstract BACKGROUND: Seed treatments with the chloronicotinyl insecticide imidacloprid (Gaucho  600 FS) were evaluated to determine whether differences in concentration and exposure regime influence the germination and early growth of rice. RESULTS: Continuous exposure to imidacloprid (4 days at 2000 mg AI L -1 ) significantly (P < 0.001) reduced normal germination by an average of 18% across the 15 cultivars examined. Nine days after sowing, plants showed no adverse effects from continuous imidacloprid treatment during germination, with shoot lengths and root system dry weights equalling, or occasionally exceeding (P < 0.05), those of untreated plants. Short-term imidacloprid exposure (2 h at 2000 mg L -1 ) at initial seed wetting did not affect germination (P > 0.05), and short-term (1 h) exposure of 48 h pregerminated seed to imidacloprid (2000 mg L -1 ) similarly had no significant effect on early subsequent growth. Plants arising from 48 h pregerminated seed exposed to imidacloprid (1 h) at concentrations up to 4000 mg L -1 immediately before sowing were not significantly different from control plants at either 9 or 25 days post-sowing. CONCLUSION: Results show that imidacloprid will have no adverse effects on plant growth if applied to pregerminated rice shortly before sowing. Continuous exposure of seed during germination had more pronounced effects, and the initial response of different cultivars was highly variable. Cultivars with high levels of sensitivity (such as IR72) require further testing before continuous exposure to imidacloprid during germination can be recommended.  2007 Society of Chemical Industry Keywords: imidacloprid; rice; phytotoxicity; germination; growth 1 INTRODUCTION Imidacloprid is a chloronicotinyl insecticide used on a range of different crops throughout the world. It has pronounced systemic activity, 1,2 which can be enhanced in foliar applications by the addition of spray additives. 2 It is often applied either to the soil or as a seed treatment 2,3 to maximise uptake into plant tissues and enhance its residual activity against pests. The use of agrochemicals as seed treatments entails both benefits and potential risks. Seed treatment delivers insecticides and fungicides to the root zone of the growing plant, allowing chemical inputs into the environment to be reduced. 4,5 In addition, seed treatment can deliver direct economic benefits to farmers by reducing both chemical and application costs, provided these savings are not exceeded by the cost of sophisticated treatment techniques such as pelleting and film coating. These benefits are balanced by an increased risk of phytotoxicity, since treated seeds are often exposed to significantly higher chemical concentrations than occur in foliar treatments applied to established plants. 5 The risk of a phytotoxic response to seed treatment is affected not just by the active chemical being applied but also by factors such as formulation type, exposure period and conditions, crop species and cultivar. Imidacloprid has been evaluated as a seed treatment on crops such as wheat, 6,7 barley 6 and forage brassicas, 8 generally without any phytotoxicity or adverse effects on plant growth being observed. Conversely, imidacloprid seed treatment has been ∗ Correspondence to: Mark M Stevens, Yanco Agricultural Institute, NSW Department of Primary Industries, Private Mail Bag, Yanco, NSW 2703, Australia E-mail: mark.stevens@dpi.nsw.gov.au (Received 15 May 2007; revised version received 26 July 2007; accepted 14 August 2007) Published online 13 December 2007; DOI: 10.1002/ps.1499  2007 Society of Chemical Industry. Pest Manag Sci 1526–498X/2007/$30.00