The effects of spinosad to beneficial insects and mites and its use in IPM.

The effects of spinosad to beneficial and non-target arthropods has been extensively researched. Data have been generated under laboratory, semi-field and field conditions on a wide range of predatory and parasitic taxa in a variety of geographical regions and crop types. Such a large body of data cannot be summarized in detail in a single publication; however, general patterns of effects exist in the data. The aim of this paper is to demonstrate the range of effects of spinosad to beneficial predatory and parasitic arthropods. This is done by presenting in detail selected laboratory, semi-field and field test with beneficial arthropods. Following that an analysis of a database of effects is conducted using records taken from Dow AgroSciences and independent reports. Using these illustrations the profile of effects on a range of predatory and parasitic arthropods are clearly defined. Research has demonstrated that when used according to good agricultural or horticultural practice spinosad is of low risk to predatory mites and beneficial insect populations. Toxicity has been reported to certain parasitic hymenoptera but due to the very short persistence of the product any effects are short lived and followed by rapid recovery. This makes the product an ideal tool in vegetable, pome and pear crops where it can be used to control, thrips caterpillar pests and Psylla. Overall, spinosad preserves natural populations of predatory mites and beneficial insects which make it an ideal choice in IPM programmes.

Field studies to determine the effects of spinosad on the predatory bugs Anthocoris nemoralis and A. nemorum.

The predatory bugs Anthocoris nemoralis and A. nemorum are important predators of the pear psylla (Psylla pyri) in pear orchards. To effectively control psylla infestations the use of insecticide treatments are often necessary so it is desirable to adopt products and use patterns which protect or conserve natural predator populations. Spinosad (the active ingredient in TRACER* insecticide) is highly active on psylla when applied up to two times after flowering. To investigate the effects of spinosad on A. nemoralis and A. nemorum a series of field trials were conducted between 1998 and 2005 in pear. Findings from these trials showed that spinosad applied at the psylla rate may cause minor short term effects on A. nemoralis and A. nemorum specifically to very young (or recently hatched) nymphs. However, due to the rapid photodegradation of spinosad recovery of predatory bug populations follows a few days after final application. The occasional depressive effect due to spinosad applications was considered to be due mainly to the removal of the pear psylla prey as spinosad has excellent efficacy on this pest. Findings from the trials demonstrated that predatory bug populations recover rapidly within a few days after the second application in order to control any new pear psylla attack. Therefore, spinosad can be considered as a valuable new tool for controlling pear psylla populations in pear orchards and to be compatible with augmented biological control by the predatory bug population.

Soil metabolism of isoxaflutole in corn.

The herbicide isoxaflutole 1 (5-cyclopropyl-4-isoxazolyl)[2-(methylsulfonyl)-4-(trifluoromethyl)phenyl]-methanone) has been applied preemergence at the rate of 125 g ha(-1) on corn crops grown on fields located in regions different as to their soil textures. Its metabolite diketonitrile 2 (2-cyano-3-cyclopropyl-1-(2-methylsulfonyl-4-trifluoromethylphenyl)propane-1,3-dione)-which is the herbicide's active compound-and its nonherbicide metabolite 3 (2-methylsulfonyl-4-trifluoromethylbenzoic acid) were measured in the 0-10 cm surface soil layer of the corn crops after the treatment and until the harvest. At the opposite of what occurred in plant shoots, the transformation of isoxaflutole 1 into diketonitrile 2 was not immediate in soil. In the 0-10 cm surface soil layer, this transformation occurred progressively according to an apparent second-order kinetics, and the soil half-lives of isoxaflutole 1 self were comprised between 9 and 18 days. The adsorption of isoxaflutole 1 onto the solid phase of the soil and its organic matter should explain the stabilization effect of soil, increased by the application of fresh organic fertilizer. The sum of the concentrations of isoxaflutole 1 and diketonitrile 2 disappeared in the 0-10 cm surface soil layer according to an apparent first-order kinetics, and the soil half-lives of this sum were comprised between 45 and 65 days. The sum of the concentrations of isoxaflutole 1 and of its metabolites diketonitrile 2 and acid 3 did not account for the amount of isoxaflutole 1 applied. The discrepancy increased with the delay after the application, showing that the acid 3 was further metabolized in soil into common nontoxic products, and ultimately into CO2. The conjunction of the adsorption of isoxaflutole and its metabolites (which reduced their mobilities) onto the soil and its organic matter, and their further metabolism should explain why isoxaflutole and its metabolites were not detected in the 10-15 and 15-20 cm surface soil layers during the crops.

Soil persistence of 4-HPPD-inhibitors in different soil types.

In field experiments carried out during the 1997-2001 period on four different soil types (sand, sandy loam, heavy sandy loam and clay) in Flanders (Belgium), the persistence of the three 4-HPPD inhibiting maize herbicides mesotrione (100 and 150 g ha-1), sulcotrione (300 and 450 g ha-1) and isoxaflutole (75 and 125 g ha-1) was studied. Therefore, soil samples were taken at regular intervals from application in spring and frozen. When all samples had been taken, greenhouse bioassays were set up to detect herbicide residues in the different soil types. Therefore, two extremely sensitive test plants, sugarbeet (Beta vulgaris L. spp. altissima Doell. var. saccharifera Deck.-Dill) and red clover (Trifolium pratense L.) were sown in the soil samples. Test plants were harvested after 2 (sugarbeet) and 3 (red clover) weeks and foliage fresh weight per plant was determined. This parameter was expressed relatively to the average fresh weight per plant of the plants sown in the control soil samples taken at each sampling date. The bioassays revealed several factors that influence the persistence of the herbicide tested. First, there is a remarkable influence of the experimental year due to variation in weather conditions (especially rainfall and temperature during the first weeks after spraying). Secondly, a different soil texture results in a highly different persistence: the shortest biological persistence was noticed each year in clay, followed by heavy sandy loam; the longest persistence was recorded in sandy and sandy loam soil types. Thirdly, there are important differences between the three herbicides tested: isoxaflutole (a member of the isoxazole chemical family) was shown to be less persistent than sulcotrione and mesotrione (both members of the triketone family). Remarkably, this was not the case in clay, where a longer persistence could be seen for isoxaflutole compared to sulcotrione and mesotrione. This study also revealed that applying a low rate results in a shorter persistence period compared to the higher rate. All these factors work together in a complex way which determines the persistence of the three herbicides tested.

Soil persistence and metabolism of iodosulfuron in winter wheat crops.

The sulfonylurea herbicide iodosulfuron 1 has been applied post-emergence at the dose of 10 g a.i. ha-1 on winter wheat crops grown on sandy-loam (Melle) or on clay soils (Leke, Gistel and Zevekote). The dissipation of iodosulfuron in soil followed a first order kinetics. After the application of iodosulfuron at Melle at the beginning of April 2000, the soil half-life of iodosulfuron in the 0-10 cm surface soil layer was 60 days. At the end of September 2000, i.e. one month after the winter wheat harvest, only 8% of the applied dose of iodosulfuron remained in soil as iodosulfuron itself. At the mid of November, iodosulfuron 1 was no more detected in the 0-10 cm surface soil layer. From the beginning of May till the end of July 2000, low concentrations of iodosulfonamide 2 and of iodosaccharin 3 were observed in the 0-10 cm surface soil layer, their maximum concentrations being 0.7 and 1.5 micrograms of equivalents of iodosulfuron 1 kg-1 dry soil, respectively. At the end of September, the metabolites 2 and 3 were no more detected in soil. At Leke, Gistel and Zevekote, iodosulfuron was applied at the beginning of May 2001, and its half-life in the 0-10 cm surface soil layer was 44, 30 and 35 days, respectively. The later application of iodosulfuron and the higher soil pH (about 8) at Leke, Gistel and Zevekote should explain the soil half-lives lower than at Melle (soil pH 6.2). In all the trials and since the treatment till the mid of November, iodosulfuron 1 and its metabolites 2 and 3 were not detected in the 10-15 and 15-20 cm surface soil layers.

Dissipation and mobility of flumetsulam in the soil of corn crops.

The triazolopyrimidine sulfonanilide herbicide flumetsulam has been applied pre- or post-emergence at the rate of 20 g a.i. ha-1 on corn crops grown on sandy-loam or loamy-sand soils. A procedure has been developed for the analysis of flumetsulam in soil using gas-chromatography and gas-chromatography combined with mass spectrometry, after methylation of flumetsulam and purification of the soil extracts by repeated thin-layer chromatographies. The dissipation of flumetsulam in the 0-8 cm surface soil layer followed a first order kinetics. The flumetsulam soil half-life was about 41 days for the crops grown on sandy-loam soil, and 30 days for the crop grown on loamy-sand soil. At the corn harvest in September, only 9 to 13% of the applied dose of flumetsulam remained in soil, what is a common value for the herbicides at the crop harvest. The heavy rains and the soft temperatures of the autumn should dissipate these low residues within the one or two months period after the harvest. When applied at the rate of 20 g a.i. ha-1, the persistence of flumetsulam in field soil thus was moderate. During the crops and until the harvest, in the 8-15 cm surface soil layer, low concentrations of flumetsulam at the limit of the analytical sensitivity (0.3 microgram flumetsulam kg-1 dry soil) were observed temporarily; in the 15-20 cm surface soil layer, flumetsulam was never detected, showing that flumetsulam was strongly adsorbed onto the soil and its organic matter.

Dissipation and mobility of the sulfonylaminocarbonyl-triazolinone herbicide propoxycarbazone in the soil of winter wheat crops.

The new sulfonylaminocarbonyltriazolinone herbicide propoxycarbazone has been applied at the rate of 70 g ha-1 post-emergence in the spring on winter wheat fields located at three sites different as to their soil texture and composition. A method has been developed for the analysis of propoxycarbazone in soil by GC and GC-MS, after isolation and transformation of propoxycarbazone. The limit of sensitivity was 1 microgram propoxycarbazone kg-1 dry soil. In the sandy-loam soil at Melle, and in the clay-loam soil at Zevekote, the propoxycarbazone soil half-lives in the 0-10 cm surface soil layer were similar, i.e. about 54 days. In the loam soil at Cortil-Noirmont, the propoxycarbazone soil half-life was 31 days. The difference as to the soil half-lives was related to the organic fertilization practized in the past on the three fields. At Cortil-Noirmont, after the winter wheat harvest at the end of August, the residues of propoxycarbazone in the 0-10 cm surface soil layer were very low, and at the end of September, propoxycarbazone was no more detected. At Melle and Zevekote, at the end of September, the concentrations of propoxycarbazone in the 0-10 cm surface soil layer were very low; at the end of October, propoxycarbazone was no more detected. After its application and until the end of October, propoxycarbazone was not detected in the 10-15 and 15-20 cm surface soil layers.

Fate of the herbicide isoxaflutole in the soil of corn fields.

The herbicide isoxaflutole 1 (5-cyclopropyl-4-isoxazolyl)[2- (methylsulfonyl)-4-(trifluoro-methyl)phenyl]-methanone) was applied pre-emergence at the rate of 125 g ha-1 on corn fields located in three sites different as to their soil texture and composition. In the 0-10 cm surface soil layer, the isoxaflutole soil half-life (soil dissipation kinetics of second order) was 9 days in sandy loam (Melle), 15 days in clay loam (Zevekote) and 18 days in loamy sand (Zingem) soil. The sum of the concentrations of isoxaflutole 1 and of its herbicide active metabolite diketonitrile 2 (2-cyano-3-cyclopropyl-1-(2-methylsulfonyl-4- trifluoromethylphenyl)propane-1,3-dione) had a soil half-life (dissipation kinetics of first order) of 45 days in sandy loam, and 63 days in the clay loam and loam sand soils. The soil metabolism of isoxaflutole thus generated, in the soil of field corn crops, a metabolite, the diketonitrile 2, which had an herbicide activity as high as the one of the parent isoxaflutole, and which much extended the herbicide protection given by isoxaflutole. At the crop harvest, isoxaflutole, the diketonitrile 2 and the acid 3 (2-methylsulfonyl-4-trifluoromethylbenzoic acid) were no more detected in soil. During the corn crops, isoxaflutole, and its metabolites diketonitrile 2 and acid 3 were never detected in the 10-15 et 15-20 cm surface soil layers, indicating the very low mobility of these compounds in soil.

Soil dissipation of diuron, chlorotoluron, simazine, propyzamide, and diflufenican herbicides after repeated applications in fruit tree orchards.

In a pear tree orchard planted on loam soil, each plot was treated in April 1998 with either one of the ureas diuron or chlorotoluron, or triazine simazine herbicides applied at 3, 4, and 2 kg AI ha(-1), respectively. Some plots had not been previously treated with one of these herbicides. Other plots had been treated annually during the past 12 years with the same herbicide. One herbicide, and always the same, was thus applied to each plot. In the plots treated for the first time with either diuron, chlorotoluron, or simazine, the soil half-lives of these herbicides in the 0-10 cm surface soil layer were 81, 64, and 59 days, respectively. In the plots treated with the same herbicide for 12 years, the corresponding soil half-lives were 37, 11, and 46 days. Diuron thus produced a moderately enhanced biodegradation, chlorotoluron a high one, and simazine a low but significant one. In another pear tree orchard planted on sandy loam soil, each plot was treated in April 1998 with one of the amide propyzamide (1.25 or 1.0 AI kg ha(-1)) or diflufenican (250 g AI ha(-1)) herbicides. In the plots not previously treated with propyzamide, the propyzamide soil half-life was the same for both doses, i.e., about 30 days. In the plots treated annually for 3 or 14 years with propyzamide, the soil half-life was 12 and 10 days, respectively. In the plots treated for the first time with diflufenican and in those treated annually with diflufenican for 3 years, the diflufenican soil half-life was the same, i.e., 65 days. Propyzamide thus already showed a highly accelerated biodegradation after 3 years of repeated annual applications. Diflufenican, however, did not show enhanced biodegradation after 3 years of repeated annual applications.