Ai Ha Research Articles

Interaction of a di-nitro aniline herbicide (Trifluralin) with soil vegetation system under sub-tropic condition: A dissipation kinetics study

A field study was carried out to investigate persistence and dissipation kinetics of Trifluralin (48 EC) applied pre emergently in Green gram (Variety T-44) @ 1 Kg ai ha-1 (T1) and 2 Kg ai ha-1 (T2) for the control of broad leaf weeds during kharif 2006. The dissipation on 90 days was around 71.56 - 64.55% in T1 and T2. Kinetics studies revealed that dissipation of Trifluralin residues followed first order kinetics. The half life values observed were 60.21 days in T1 and 75.56 days in T2. Irrespective of any dose no residues were detected in cropped soil as well as plant samples at harvest.

Suppression of volunteer potatoes with maleic hydrazide applications

Volunteer potato plants are difficult weeds to control in a wide variety of rotation crops and are not effectively controlled by tillage and herbicides because buried tubers can vigorously resprout. Maleic hydrazide (MH) may provide some of the needed control. This study investigated the efficacy of MH applications for volunteer plant suppression. ‘Russet Burbank’, ‘Ranger Russet’, ‘Russet Norkotah’ and ‘Shepody’ plants were treated with 3.4 kg ai ha-1 Royal MH-30 Xtra® (MH) each of three years. Tuber samples (<57, 57 to 113, 113 to 284 g) were assayed for MH residue and planted the following spring to measure plant emergence.

Comparison of weed control strategies in glyphosateresistant soybean [Glycine max (L.) Merr.] in Atlantic Canada

Glyphosate-resistant soybean cultivars with low corn heat unit requirements have only recently become available in the Atlantic region of Canada. In a field experiment near Charlottetown, Prince Edward Island, in 1998 and 1999, we evaluated the effect of time of application of glyphosate and application of selected herbicides, flumetsulam, metolachlor, imazethapyr, metribuzin, and bentazon on weed control and tolerance and yield of three glyphosate-resistant soybean cultivars having different maturity ratings. Glyphosate was applied at 0.90 kg ai ha-1 at the first, second or third trifoliate leaf stage, and sequentially at the first and third or second and third trifoliate stages. The sequential treatments of glyphosate resulted in 89 to 100% weed control, and yields achieved with glyphosate applied at the second or third trifoliate stages did not usually differ from sequential treatments. The other selected herbicides did not injure the cultivars and within the group, all treatments resulted in comparable yields. Species that emerge in a single early-season flush were controlled at 6 wk after treatment with glyphosate applied as a single application, but not on a species such as wild radish that have later flushes or emerge throughout the season. Glyphosate applied as a single application at the late second to third trifoliate stage can provide optimum weed control and crop yield with lower herbicide cost than an alternative herbicide treatment. Key words: Herbicide timing, narrow-row soybean, soybean cultivars, 2601R, 2701R, S14-M7

The genome sequence analysis of H5N1 avian influenza A virus isolated from the outbreak among poultry populations in Thailand

In this report, the genome of the Thai avian influenza virus A (H5N1); A/Chicken/Nakorn-Pathom/Thailand/CU-K2/04, isolated from the Thai avian influenza A (AI) epidemic during the early of 2004 was sequenced. Phylogenetic analyses were performed in comparison to AI viruses from Hong Kong 1997 outbreaks and other AI (H5N1) isolates reported during 2001–2004. Molecular characterization of the Thai AI (H5N1) HA gene revealed a common characteristic of a highly pathogenic AI (HPAI), a 20-codon deletion in the neuraminidase gene, a 5-codon deletion in the NS gene and polymorphisms of the M2 and PB2 genes. Moreover, the HA and NA genes of the Thai AI displayed high similarity to those of the AI viruses isolated from human cases during the same epidemic. Finally, our results demonstrated that the Thai AI emerged as a member of 2000's AI lineage with most of the genetic sequences closely related to the Influenza A/Duck/China/E319.2/03 (H5N1).

Sulfosulfuron effects on growth and photosynthesis of 15 range grasses

We conducted greenhouse experiments to compare photosynthetic and growth responses of 2 invasive annual grasses (downy brome = Bromus tectorum L. and medusahead = Taeniatherum caput-medusae (L.) [Nevski]), 6 caespitose grasses, and 7 rhizomatous grasses to the herbicide sulfosulfuron (1-(2-ethylsulfonylimidazo[1,2-a]pyridin-3-ylsulfonyl)-3-(4,6-dimethoxypyrimidin-2-yl)urea). Our objectives were to identify general patterns of species responsiveness and test the hypothesis that sulfosulfuron induced reduction in photosynthetic activity and shoot growth would be more pronounced in small relative to larger plants. Small plants in a spring experiment and large plants in a summer experiment were treated with sulfosulfuron (70 g ai ha-1). Wildryes and bromes were consistently injured; whereas, 5 of the 7 wheatgrasses were not susceptible to sulfosulfuron. Rhizomatous grasses generally experienced greater damage from sulfosulfuron than caespitose grasses. These results suggest that sulfosulfuron would provide a useful rangeland management tool to control unwanted invasive annual grasses without significantly hindering growth and physiology of desirable rangeland grasses.

Saltcedar Recovery after Herbicide-Burn and Mechanical Clearing Practices

Mechanical clearing and herbicide-burn treatments were compared to evaluate saltcedar (Tamarix chinensis Lour.) control and recovery along the Rio Grande on the Bosque del Apache National Wildlife Refuge, Socorro, N.M. The herbicide-burn treatment included an aerial application of imazapyr (+)-2-[4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1H-imidazol-2-yl]-3-pyridinecarboxylic acid] + glyphosate [N-(phosphono-methyl)glycine] (0.6 + 0.6 kg ai ha-1 rate) followed 3 years later by a prescription broadcast fire that eliminated > 99% of the standing dead stems. Six years after initial herbicide application, saltcedar mortality was 93%. Mechanical saltcedar clearing entailed removing aerial (trunks and stems) growth by blading, stacking and burning debris, followed by removal of underground plant portions (root crowns) by plowing, raking, and burning stacked material. Saltcedar mortality 3 years after mechanical clearing averaged 70%, which was deemed unsatisfactory. Thus, root plowing, raking, and pile burning was repeated. Three years later, after the second mechanical clearing, saltcedar mortality was 97%. Costs for the herbicide-burn treatment averaged $283 ha-1, whereas mechanical control costs were $884 ha-1 for the first surface and root clearing and an additional $585 ha-1 for the second root clearing. Riparian managers should consider environmental conditions and restoration strategies prior to selecting a saltcedar control approach. Although control costs were significantly lower for the herbicide-burn treatment compared to mechanical clearing in this study, the choice of methods should always consider alternative control strategies for saltcedar. Frequently, combinations of methods result in more efficient, cost-effective results. DOI:10.2458/azu_jrm_v56i5_mcdaniel

Saltcedar recovery after herbicide-burn and mechanical clearing practices

Mechanical clearing and herbicide-burn treatments were compared to evaluate saltcedar (Tamarix chinensis Lour.) control and recovery along the Rio Grande on the Bosque del Apache National Wildlife Refuge, Socorro, N.M. The herbicide-burn treatment included an aerial application of imazapyr (+)-2-[4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1H-imidazol-2-yl]-3-pyridinecarboxylic acid] + glyphosate [N-(phosphono-methyl)glycine] (0.6 + 0.6 kg ai ha-1 rate) followed 3 years later by a prescription broadcast fire that eliminated &gt; 99% of the standing dead stems. Six years after initial herbicide application, saltcedar mortality was 93%. Mechanical saltcedar clearing entailed removing aerial (trunks and stems) growth by blading, stacking and burning debris, followed by removal of underground plant portions (root crowns) by plowing, raking, and burning stacked material. Saltcedar mortality 3 years after mechanical clearing averaged 70%, which was deemed unsatisfactory. Thus, root plowing, raking, and pile burning was repeated. Three years later, after the second mechanical clearing, saltcedar mortality was 97%. Costs for the herbicide-burn treatment averaged 283 ha-1, whereas mechanical control costs were 884 ha-1 for the first surface and root clearing and an additional 585 ha-1 for the second root clearing. Riparian managers should consider environmental conditions and restoration strategies prior to selecting a saltcedar control approach. Although control costs were significantly lower for the herbicide-burn treatment compared to mechanical clearing in this study, the choice of methods should always consider alternative control strategies for saltcedar. Frequently, combinations of methods result in more efficient, cost-effective results.

Target sites for herbicides: entering the 21st century.

At present the use-rate of modern herbicides is in the range of 100-300 g AI ha-1, with a tendency to decline. The low use-rate (ca 10 g AI ha-1) of the original sulfonylurea and cyclic imide herbicides prompted agrochemical scientists to look for even more active compounds which led to the successive discoveries of many new herbicidal acetolactate synthase inhibitors and no less than 18 cyclic imides in the class of protoporphyrinogen-IX oxidase inhibitors in the 1990s. In this paper, mechanisms of action related to function and biosynthesis of chlorophylls, carotenoids, plastoquinone, amino acids, fatty acids and photosynthetic electron transport and other metabolic processes are discussed as plant-specific herbicidal target domains.

Activity of mesotrione on resistant weeds in maize.

Mesotrione is a new callistemone herbicide that inhibits the HPPD enzyme (p-hydroxyphenylpyruvate dioxygenase) and introduces a new naturally selective tool into weed-management programmes for use in maize. Mesotrione provides control of the major broad-leaved weeds, and it can be used in integrated weed-management programmes depending on the grower's preferred weed-control strategy. At post-emergence rates of 150 g AI ha-1 or less, mesotrione provides naturally selective control of key species that may show triazine resistance (TR), e.g. Chenopodium album L, Amaranthus species, Solanum nigrum L, as well as species of weed that show resistance to acetolactase synthase (ALS) inhibitors e.g. Xanthium strumarium L, Amaranthus spp and Sonchus spp. The data presented show that resistant and susceptible biotypes of these species with resistance to triazine herbicides, such as atrazine, simazine, terbutylazine and metribuzin, or ALS-inhibitor herbicides, such as imazethepyr, remain susceptible to mesotrione. These results confirm that there is no cross-resistance in biotypes with target site resistance to triazine or ALS-inhibiting herbicides. It is important that herbicide choice and rotation becomes an integral part of planning weed management, so as to minimise the risks of crop losses from weed competition, build-up of weed seed in the soil and the further development of weed resistance across a range of herbicide modes of action.

Efficiency and profitability of an IPM package against insects, blast, and nematodes in irrigated rice

In Burkina Faso, major biotic constraints to rice production in irrigated conditions include insects, diseases, and nematodes. Lepidopterous stem borers (Chilo zacconius, C. diffusilineus, Maliarpha separatella, and Sesamia calamistis) can cause up to 33% yield losses (Dakouo et al 1991). A 1% increase in damage of the African rice gall midge is correlated with a 2% yield loss (Nacro et al 1996). Pot trials showed a yield loss of 30% caused by rice root nematode Hirschmaniella spinicaudata (Thio 1992). Rice blast (caused by Pyricularia oryzae) causes yield losses with an estimated value of more than US$10 million in West Africa (WARDA 1995). Pest control in irrigated rice still largely depends on the use of chemicals without meeting the necessary criteria of efficiency and profitability for small-scale farmers. Therefore, a cost-effective integrated pest management (IPM) package was developed by a multidisciplinary team to minimize reliance on toxic and expensive chemicals. This IPM package combines the use of local natural products made of organic manure (5 t ha-1) against nematodes, rice straw ash (2.5 t ha-1) against blast, dry neem (Azadirachta indica) leaf powder against nematodes, and alcoholic extracts of neem seed powder (200 g into 0.25 L of alcohol and 0.75 L of water) against insects. The efficiency and profitability of the package were evaluated during the 2000 wet season at two irrigated rice schemes, Banzon and Karfiguela, near Bobo-Dioulasso, southwest Burkina. Its efficiency was optimized with the use of a rice gall midge-tolerant variety, BW 348-1. The IPM package (T3) was compared with two other treatments, T1 and T2. The first treatment (T1) was the control with no products against pests. T2 was a reference chemical treatment combining the insecticide Basudin (diazinon) at 1,000 g ai ha-1 in foliar sprays at 20, 40, and 60 d after transplanting (DAT), the nematicide Basamid (dazomet) at 100 kg ha-1 (incorporated into the soil 14 d before transplanting), and the fungicide Kitazin (di-isopropyl-sbenzil-thiophosphate) in a foliar spray at 720 g ai ha-1 at panicle emergence. The experimental design was a completely randomized block with three treatments and four replications, a plot size of 60 m2 (10 6 m), and plant density of 25 25 cm. Insect damage (deadhearts and onion shoots) was assessed at 40, 60, 80, and 100 DAT. Foliar blast was evaluated at 35, 49, and 63 DAT and neck blast incidence at 15 and 30 d after panicle emergence (DAPE). Nematode populations were estimated at the time of Basamid application—before transplanting and at 30, 60, 90, and 120 DAT.

Drymatter production and nutrient uptake as influenced by mepiquatchloride in potato

Field experiments were conducted during 1997-98 at wood house farm, Udhagamandalam to study the effect of mepiquatchloride (MC) at different concentration from 50 to 250 gai ha compared along with pesticides, water spray and control. Plant samples were collected at 60 and 90 DAS and at harvest and analyzed for N, P and K contents. The results indicated that, foliar application of MC at 45 DAS recorded increased Total dry matter production (TDMP), nutrient content and uptake in the treatment of MC at 62.5 g ai ha-1 alone or in combination with endosulfan and mancozeb.

Persistence and performance of esfenvalerate residues on broccoli.

The efficacy of esfenvalerate (84 g litre-1 EC; Asana XL) at 7.0 g AI ha-1 on broccoli was tested against the flea beetle, Phyllotreta cruciferae Goeze (Chrysomelidae: Coleoptera) and the imported cabbage worm, Pieris rapae L (Pieridae: Lepidoptera) under field conditions. Insect populations were monitored before and after treatment. Periodic sweep-net collections and examination of the leaves in treated and untreated broccoli plots revealed mean reductions of P cruciferae levels of nearly 98% 1 week post-application compared with untreated plots. The residual toxicity of esfenvalerate was also effective for 2 weeks in reducing population density of P rapae by 69% on broccoli leaves. The impact of esfenvalerate on feeding damage to broccoli leaves was established by counting the number of feeding holes made by P cruciferae on spring broccoli and P rapae on fall broccoli. As the leaf area ingested increased, a linear relationship was seen between the number of holes and number of insects. Results indicated that forage destruction by the two pests was significantly reduced by esfenvalerate application. Esfenvalerate was extracted from broccoli at 1 h and 1, 3, 7, 10, and 14 days post-application for residue analysis. Residues on spring broccoli were 12.2, 5.2 and 2.9 micrograms cm-2 on the leaves and 0.13, 0.05 and 0.02 microgram g-1 on the heads at 1 h, 1 and 3 days, respectively. Only trace levels (0.001 microgram g-1) were detected in/on the heads 14 days after spraying. On the basis of half-life (T1/2) values, persistence of esfenvalerate on spring broccoli leaves (T1/2 = 1 day) was shorter than on fall broccoli (T1/2 = 1.6 days). T1/2 values were 2.1 and 3.6 days on spring and fall broccoli heads, respectively. The implications of these residue levels on re-entry times into treated fields are discussed.

Microscopic analysis of the effect of azoxystrobin treatments on Mycosphaerella graminicola infection using green fluorescent protein (GFP)-expressing transformants.

Green fluorescent protein (GFP)-expressing transformants were used to investigate the effects of strobilurin fungicide azoxystrobin on Mycosphaerella graminicola infection. Azoxystrobin treatments (125 or 250 g AI ha-1) were applied at various stages of the infection process under controlled conditions. GFP transformants showed conserved in vitro sensitivity to azoxystrobin and pathogenicity. Azoxystrobin controlled over 90% of M graminicola infections when applied before or during penetration of the pathogen (15% of the incubation phase). Azoxystrobin also impaired the growth of intercellular hyphae in M graminicola post-penetration infection stages when applied at up to 50% of the incubation phase. Incubating infections observed in treated leaves were viable, but their growth was impaired and they did not induce necrosis under controlled conditions. Reduction by half of azoxystrobin dosage had little or no effect on azoxystrobin efficiency in controlling M graminicola. The contribution of post-penetration fungistatic effect to azoxystrobin curative properties toward M graminicola in a field situation is discussed.

Degradation of imazosulfuron in soil.

Imazosulfuron, 1-(2-chloroimidazo[1,2-alpha]pyridin-3-ylsulfonyl)-3- (4,6-dimethoxypyrimidin-2-yl)urea, is a new post-emergence sulfonylurea herbicide applied once per growing season, highly active at low application levels, used to control most annual and perennial broad-leaf weeds and sedges in paddy rice (75-95 g AI ha-1) and turf (500-1000 g AI ha-1), and characterised by low mammalian toxicity. The degradation of imazosulfuron in a sandy loam soil (10-15 cm depth) has been investigated under aerobic and anaerobic laboratory conditions to evaluate its likely environmental fate. Test soils were treated with imazosulfuron in acetonitrile to give a final concentration of 0.2 mg kg-1 (100 g ha-1). The treated soils were extracted with methylene chloride + acetonitrile + 1 M ammonium hydroxide (4 + 15 + 1 by volume) and analysed by HPLC. Recoveries from spiked soils ranged from 80% to 95% (RSD 0.5-2.5%; n = 3) for imazosulfuron and its metabolites 2-chloroimidazo[1,2-alpha]pyridin-3-sulfonamide (IPSN), 1-(2-chloroimidazo[1,2-alpha]pyridin-3-ylsulfonyl)-3-(4-hydroxy-6- methoxypyrimidin-2-yl)urea (HMS) and 2-amino-4,6-dimethoxypyrimidine (ADPM). The limits of quantitation ranged from 0.001 mg kg-1 to 0.005 mg kg-1. Chemical cleavage of the sulfonylurea bond to give ADPM and IPSN was the main degradation pathway in aerobic conditions, whereas a remarkable production of HMS under anaerobic conditions suggested that degradation was due to micro-organisms which had the ability to demethylate imazosulfuron. In aerobic and anaerobic conditions, imazosulfuron disappeared from the soil with a half-life of approximately 70 (90% CL 62-75; r2 = 0.98) and 4 (90% CL 3.2-4.2; r2 = 0.97) days, respectively.

Influence of adjuvants on tetrapion efficacy for nassella tussock (Stipa trichotoma Nees) control and subsequent seedling establishment: a preliminary study

Nassella tussock (Stipa trichotoma Nees) is a perennial grass weed that seeds prolifically, resulting in build-up of a large soil seed bank. Due to it's vigorous growth it has the potential to spread rapidly in disturbed environments and overgrazed areas. Field trials were initiated in a dense nassella tussock infestation to assess the influence of various adjuvants (Citowett, Frigate and Reverseal 9) on the herbicide activity of tetrapion (sodium 2, 2, 3, 3-tetrafluoropropion) and to monitor subsequent seedling establishment. Reverseal 9 was the only adjuvant that significantly increased the efficacy of tetrapion at 0.44kg ai ha1, but this level of control achieved (75%) was not considered adequate for large-scale nassella tussock control operations. The next higher rate of tetrapion (0.88 kg ai ha1) was effective in achieving nearly total mortality (98%) with or without the addition of Reverseal 9. This rate also restricted establishment of nassella tussock seedlings for up to 23 months after initial application. Further studies with tetrapion/Reverseal 9 combinations are recommended in an attempt to reduce the current registration rate of tetrapion (0.88kg ai HEN), thereby saving costs and reducing the negative impact on desirable grasses and subsequent veld rehabilitation.

The commercial use of azadirachtin and its integration into viable pest control programmes

With the continued robust growth of the global biopesticide market, azadirachtin is uniquely positioned to become a key insecticide to expand in this market segment. In the USA the actual or impending cancellation of some organophosphate and carbamate insecticides that have either lost patent protection or are not being re-registered in many markets because of the Food Quality Protection Act of 1996, has opened new opportunities for biopesticides and reduced-risk pesticides in general. The broad-spectrum activity of azadirachtin at low use rates (12·5 to 40 g AI ha-1) coupled with the insect growth regulator activity (in all larval/nymphal instars including the pupal stage) and unique mode of action (ecdysone disruptor), make azadirachtin an ideal candidate for insecticide resistance, integrated pest control and organic pest control programmes. Azadirachtin has been exempted from residue tolerance requirements by the US Environmental Protection Agency for food crop applications. Azadirachtin exhibits good efficacy against key pests such as whiteflies, leafminers, fungus gnats, thrips, aphids and many leaf-eating caterpillars. Azadirachtin has minimal to no impact on non-target organisms, is compatible with other biological control agents and has a good fit into classical Integrated Pest Management programmes. The world's largest azadirachtin extraction facility has been fully commissioned in India to process over 10,000 tonnes neem seeds per annum. This will ensure the wide availability of azadirachtin technical grade material in the future. © 1998 Society of Chemical Industry.

Residues and fate of endosulfan on field-grown pepper and tomato

Endosulfan (Thiodan 3 EC), a mixture of α- and β-isomers, was sprayed on 92-day-old field-grown pepper and tomato at the recommended rate of 0·61 kg AI ha-1. Plant tissue samples were collected at 1 h to 14 days after application and analysed to determine the content and dissipation rate of endosulfan isomers (α- and β-endosulfan) and the major metabolite, endosulfan sulfate. Analysis of samples was accomplished using gas chromatography-mass selective detection (GC-MSD). The results indicated the formation of endosulfan sulfate as a residue component on the plant tissues and also the relatively higher persistence of the β-isomer as compared to the α-isomer on pepper fruits. The initial total residues (α- and β-endosulfan isomers plus endosulfan sulfate) were higher on leaves than on fruits. On pepper fruits, the α-isomer, which is the more toxic to mammals, dissipated faster than the less toxic β-isomer. Total residues (α- and β-endosulfan isomers plus the sulfate metabolite) on tomato leaves revealed longer persistence (t1/2 4·6 days) compared to the total residues detected on pepper leaves (t1/2 2·0 days) 3–14 days following spraying. Persistence of the β-isomer on pepper fruits was high 3–14 days following spraying compared to on tomato fruits. This long persistence increases risk of exposure of the consumer. In addition, the longer persistence of the total residues on tomato foliage should be considered of importance for timing the safe entry of tomato harvesters due to the high mammalian toxicity of endosulfan. © 1998 Society of Chemical Industry

Fate of chlorsulfuron in the environment. 2. Field evaluations

The fate and mobility of chlorsulfuron was determined in several field studies with 14C-labeled chlorsulfuron. A study comparing fall with spring applications (∽100 g AI ha-1) to in-situ soil columns (35 cm depth) in neutral to alkaline soils (pH 6·9–8·2, OM 1·0–5·3) located in CO, ID and ND demonstrated that fall treatments did not persist longer into the following year than spring treatments. Mobility into the soil profile appeared to be initially faster following fall applications at the ID and ND sites, but differences between application seasons appeared to moderate with time. A field-soil metabolism study conducted at Madera, CA on a sandy loam soil (pH 6·3–6·9 and 0·3–0·4% OM with depth) with chlorsulfuron (∽158 g AI ha-1) demonstrated rapid dissipation of chlorsulfuron (pseudo-first-order half-life 18 days). No intact chlorsulfuron was found after the 120-day sampling. Major metabolites observed in this study were chlorobenzenesulfonamide (2-chlorobenzenesulfonamide) and triazine amine (4-methoxy-6-methyl-1,3,5-triazin-2-amine), products of bridge cleavage, and O-desmethylchlorsulfuron (1-(2-chlorophenylsulfonyl)-3-(4-hydroxy-6-methyl-1,3,5-triazin-2-yl)urea). No intact chlorsulfuron was detected below the 0–15 cm layer at any sampling (maximum depth 60–90 cm), but chlorobenzenesulfonamide and ring-opened carbamoyl guanidine (1-(2-chlorophenylsulfonyl)-3-(ureido-imino)urea) were found at the 15–30 cm depth. In a similar study conducted on a silt loam soil in Moscow, ID (pH 6·1–6·9 and 2·2–1·0% OM with depth), overall dissipation was much slower than at Madera, CA due to the cooler climate (average soil temperature 8·6° versus 20·0°). The initial rate of chlorsulfuron dissipation was similar (pseudo-first-order half-life 18 days), but dissipation exhibited a distinctly slower second stage (half-life 109 days) not exhibited at Madera, CA. By the 370-day sampling no intact chlorsulfuron was detected. The chlorobenzenesulfonamide and triazine amine were the major metabolites found in this study, accounting for approximately 38 and 30%, respectively, of the initial chlorsulfuron at the last sampling (571 days). Other metabolites were found in lesser amounts, including O-desmethylchlorsulfuron, ring-opened carbamoyl guanidine, hydroxy triazine amine (4-amino-6-methyl-1,3,5-triazine-2-ol), triazine urea ((4-methoxy-6-methyl-1,3,5-triazin-2-yl)urea), an undifferentiated bound fraction and an unidentified group of polar components. The presence of triazine urea indicates that soil-surface photolysis (or indirect photolysis) may have been operative. In the study in Moscow, ID, no intact chlorsulfuron was found below the 0–15 cm layer at any sampling (maximum depth 75 cm). Movement of total radioactive components was restricted to a maximum depth of 60 cm at Madera, CA and 50 cm at Moscow, ID. The overall water balance over the duration of both studies was negative, helping to explain the observed lack of leaching. The PRZM3 model was used to predict the distribution profile of chlorsulfuron at the Moscow, ID site for which the base case overpredicted leaching (down to 20–30 cm) and predicted the depletion of the surface layer, which did not occur. The prediction was improved by arbitrarily doubling the Koc value and using a slightly higher than measured soil bulk density. © 1998 SCI

Persistence and mobility of tebufenozide in forest litter and soil ecosystems under field and laboratory conditions

A field microcosm study was conducted to determine persistence of tebufenozide, an insect growth regulator, in sandy litter and soil. Litter and soil plots (c. 4·5 m2 each) were sprayed with an aqueous suspension concentrate formulation of tebufenozide at rates of 35, 70 and 140 g AI ha-1. Samples were collected at intervals up to 408 days after spraying, and analyzed for tebufenozide residues. The data were subjected to regression analysis and half-life (DT50, the time required for 50% of the initial residues to disappear) values were computed. The DT50 was c. 62 days for both substrates treated with the two lower dosage rates. At the highest dosage rate, the DT50 was 115 days for the litter and c. 52 days for the soil, indicating irregular variations in persistence. Downward movement in soil occurred only in trace amounts, suggesting strong adsorption. Laboratory microcosm studies were conducted to investigate the relative importance of rainfall, exposure to light and volatilization on persistence. Vertical movement occurred in litter and soil (both sandy and clay types) during rainfall. The amount moved increased with the amount of rainfall, but decreased with the rain-free period. The larger the rain droplets, the greater the downward movement. When the rainwater could move laterally along the surface of the substrate (as would occur on a slope), more lateral movement than vertical movement of tebufenozide occurred. The photolysis study indicated that disappearance of tebufenozide was directly related to the duration of exposure to radiation and radiation intensity. Volatilization of tebufenozide depended upon the ambient temperature and the duration of air passing through the substrates. Nonetheless, the amount lost by volatilization was much lower than the amount lost after rainfall or exposure to radiation, thus indicating the greater influence of rainfall and sunlight on persistence. In the laboratory microcosm studies, more tebufenozide was lost from the sandy substrates than from the clay substrates. This behaviour was attributed to the greater adsorptive capacity of the clay substrates, thus providing a greater protection against downward mobility and loss due to radiation. © 1997 SCI

Field Dissipation of Cloransulam-methyl at Four Sites in the U.S. Soybean Market

The soil dissipation of cloransulam-methyl was studied using 14C-labeled and non-radiolabeled material in Wisconsin, Indiana, Mississippi, and North Carolina between 1993 and 1995. The test substance was pre-emergence broadcast-applied at target rates of 50 and 61.5 g ai ha-1 for the 14C-labeled and the non-radiolabeled studies, respectively. Bromide was used to track water movement at the NC and WI sites. The degradation of cloransulam-methyl was rapid and best characterized by a two-compartment model resulting in initial-rate half-lives ranging from 2.5 to 4.8 days at the MS, IN, and WI sites and by a first-order degradation model at the NC site with a half-life of 11.2 days. The rapid dissipation rates, metabolite formation patterns, and sorption characteristics obtained in this field study were consistent with the existing laboratory data generated for cloransulam-methyl. Rapid degradation rates and the increasing sorption to soil over time resulted in low persistence and mobility of this compound. Keywords: Cloransulam-methyl; triazolopyrimidine sulfonanalide; soil dissipation