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The earthworm Eukerria saltensis can cause severe crop establishment problems in aerially sown rice grown on heavy clay soils in southern Australia. Damage occurs indirectly through destabilization of the topsoil, increased water turbidity, and mobilization of soil nutrients into the water column which leads to increased algal growth. We investigated the possibilities for chemical control of E. saltensis using laboratory bioassays and a series of field trials involving either the use of enclosures in flooded crops or soil incorporation of pesticides into rice fields during fallow periods or shortly before flooding. The four most toxic compounds in 7 day soil/water laboratory bioassays were carbofuran, acetamiprid, bendiocarb and lambda-cyhalothrin which provided corrected mortalities of 86–100% at 2 mg a.i. L −1 . Other compounds that showed some level of efficacy (corrected mortality >20% at one or more rates) were imidacloprid, esfenvalerate, thiacloprid, niclosamide and alpha-cypermethrin. Twenty-six of the 38 pesticides evaluated failed to produce mean corrected mortalities >6% at application rates of up to 2 mg a.i. L −1 . Eight trials were conducted in flooded rice crops using small stainless steel enclosures and carbofuran, thiodicarb, niclosamide and bendiocarb at rates of 1 and 2 kg a.i. ha −1 . Trials were assessed 8–14 days after chemical application. None of these treatments produced a statistically significant decrease in Eukerria biomass, although consistent downward trends in response to higher treatment rates were evident in 2 trials (one with carbofuran and one with bendiocarb). Three trials with liquid pesticides watered into fallow rice fields were conducted with carbofuran (0.5, 1.0 and 5.0 kg a.i. ha −1 ) and thiodicarb (0.94 and 1.87 kg a.i. ha −1 ) however only the 5.0 kg a.i. ha −1 carbofuran treatment provided significant ( P < 0.05) levels of control. Preflood soil applications of liquid carbofuran, thiodicarb and niclosamide (2 kg a.i. ha −1 ), granular carbofuran and granular ethoprophos (0.5–2 kg a.i. ha −1 ) also did not provide statistically significant levels of control, although the 2 kg a.i. ha −1 liquid and granular carbofuran treatments did provide moderate levels of suppression (49–84%). Although further field trials with compounds such as acetamiprid and lambda-cyhalothrin may prove valuable, our results suggest chemical control of E. saltensis may be difficult to achieve with environmentally acceptable pesticides applied at economically viable rates. Cultural approaches such as appropriate crop rotations and landforming to ensure uniformly shallow water should continue to form the basis of Eukerria management programs. [ABSTRACT FROM AUTHOR]

Copper sulphate pentahydrate (CuSO 4 ·5H 2 O) is widely used for controlling Isidorella newcombi , an aquatic snail that causes substantial damage to rice crops in southeastern Australia. We conducted field trials on a Birganbigil clay loam soil that demonstrate high levels of efficacy against adult I. newcombi (95% mortality at 6.38 kg ha −1 CuSO 4 ·5H 2 O (1.14 mg Cu L −1 )). Dissolved copper fell below the detection limit (0.02 mg Cu L −1 ) between 7 and 20 d after spraying at application rates up to 2.16 mg Cu L −1 (12 kg ha −1 CuSO 4 ·5H 2 O). Total copper concentrations in the water column fell below the detection limit (0.007 mg Cu L −1 ) 7–12 d after spraying at initially applied concentrations of 0.52–1.12 mg Cu L −1 , but remained detectable (0.01–0.02 mg Cu L −1 ) until 30 days after spraying (the conclusion of monitoring) when applied at higher initial concentrations (1.18–2.16 mg Cu L −1 ). There was a strong positive correlation ( r 2 = 0.90, P < 0.001) between copper application rate and copper concentrations in surface sediments 30 d after spraying. Bioassays with immature snails using three different test soils beneath irrigation water showed that underlying soil type strongly influenced the response of snails to applied copper, with significant ( P < 0.05) differences between LC 90 values which ranged from 0.41 to 1.04 mg applied Cu L −1 . Laboratory studies showed that dissolved copper concentrations remained significantly higher ( P < 0.05) in the water column above the soil that had the most deleterious effect on copper toxicity. Dissolved organic carbon concentrations were significantly ( P < 0.05) higher in both this soil and in the overlying water in the corresponding bioassay system, and correlated more closely with LC 90 values than other water chemistry parameters such as total hardness. Our results support the ongoing use of a variable copper application rate of 6–12 kg ha −1 CuSO 4 ·5H 2 O to allow for site-specific variations in efficacy, and suggest that variations in the release of dissolved organic carbon compounds from flooded soils may be a key factor moderating copper toxicity to I. newcombi in rice fields. [ABSTRACT FROM AUTHOR]

Laboratory bioassays (48 h duration, 25 ± 1 °C) were used to determine the toxicity of Bacillus thuringiensis var. israelensis (B.t.i.) and Bacillus sphaericus to fourth instar larvae of Chironomus tepperi, a major pest of rice in southern Australia. Bioassays were conducted using different combinations of larval ages and densities to determine if these factors affected toxicity. The effects of temperature and substrate type on B.t.i. toxicity were also investigated. Tests were conducted using a commercial B.t.i. formulation (VectoBac WDG, 3000 ITU/mg), a spore/crystal mixture derived from the VectoBac WDG strain, and VectoLex WDG, a commercial B. sphaericus formulation (650 ITU/mg). VectoBac WDG was highly toxic to fourth instar C. tepperi in bioassays using a sand substrate (LC50 0.46 mg/L, older larvae); younger fourth instar larvae were more susceptible (LC50 0.20 mg/L). Increasing larval densities (from 10 to 30 per bioassay cup) increased LC50 values for both age groups, significantly so in the case of older larvae (higher density LC50 0.80 mg/L). Use of a soil substrate increased the LC50 value (older larvae, 10 per cup) to 0.99 mg/L. Similar differences in toxicity relative to larval age and substrate type were found in bioassays using the B.t.i. spore/crystal mixture. VectoBac WDG and the spore/crystal mixture both showed similar (approximately 6-fold) declines in activity between 30 and 17.5 °C. At lower temperatures (between 17.5 and 15 °C), activity of the spore/crystal mixture declined much more rapidly than that of VectoBac WDG. VectoLex WDG showed very low toxicity to C. tepperi larvae, and the overall impact of larval age and density was relatively minor (LC50 values 1062–1340 mg/L). Autoclaving VectoLex WDG did not substantially reduce its toxicity (LC50 1426 mg/L), suggesting that formulation additives (i.e., surfactants and other adjuvants) are responsible for much of the toxicity occurring at the high product concentrations required to cause C. tepperi mortality. Whilst VectoLex WDG was ineffective against C. tepperi, VectoBac WDG has the potential to provide selective control of this rice pest at economically viable application rates. [Copyright &y& Elsevier]