Absorption of 2,4-D [(2,4-dichlorophenoxy)acetic acid], dicamba [3,6-dichloro-o-anisic acid], and the isopropylamine salt of glyphosate [N-(phosphonomethyl)glycine] by excised honeyvine milkweed [Cynanchum laeve (Michx.) Pers.] leaves was determined. Experimental variables included leaf position (terminal vs. basal), a surfactant, 4-isopropenyl-1-methylcyclohexane plus unspecified emulsifiers (SA-77), and leaf collection dates. Absorption of the three herbicides by terminal and basal leaves was increased by the addition of the surfactant. However, the surfactant increased absorption into basal leaves more than into terminal leaves. The surfactant reduced surface tension and increased drying time of water droplets on adaxial leaf surfaces by 50%. The pH of the herbicide solutions was reduced from about 5.8 to about 3.9 by SA-77. Absorption of all three herbicides was greater into terminal than into basal leaves when the surfactant was added. Generally, no differences were observed in the absorption of 2,4-D and dicamba. Glyphosate absorption was greater in terminal leaves collected after a period of adequate moisture than after a period of dry soil conditions.
2011年10月11日星期二
2011年10月10日星期一
Pencycuron Dissipation in Waterlogged Rice Soil
R. Pal , K. Chakrabarti , A. Chakraborty and A. Chowdhury
ABSTRACT
________________________________________
Pencycuron dissipation in soils of waterlogged rice field was investigated at Field Rate (FR), 2FR and 10FR with and without Decomposed Cow Manure (DCM) for two consecutive years. Pencycuron dissipated at all treatment combinations following first order kinetics and the half-lives ranged between 4.9 to 5.8 days. DCM amendment has significantly accelerated the pencycuron dissipation.
Introduction
Pencycuron [1-(4-chlorobenzyl)-1-cyclopentyl-3-phenylurea] is a non-systemic protective fungicide for controlling sheath blight (Rhizoctonia solani) of rice (Tomlin, 1997). Dissipation of pencycuron in soil under laboratory condition (Pal et al., 2005a, c) and in rice plant under field has been reported (Pal et al., 2005b). However, information on the dissipation of pencycuron in soil under actual field condition is lacking. Laboratory results do not necessarily reflect the actual field condition because in field multiple forces simultaneously works (Racke et al., 1997). In addition unrealistic pesticide concentrations not relevant to agricultural management practices may be useful for assessing the environmental risk due to monocultural practices or accidental spills (Perucci et al., 1999). Tropical soils are deficient in organic matter content. Therefore, it is necessary to apply organic supplements to soil on a sustained basis. Rice is the principal crop grown in the tropics, under waterlogged condition during monsoon season. Therefore, field study under rice cultivation was conducted to determine the dissipation of pencycuron in soil.
Materials and Methods
Field experiments were conducted for two consecutive years in the wet seasons (June-October) of 2002 and 2003 at the Agriculture Experimental Farm, Bidhan Chandra Krishi Viswavidyalaya, Mohanpur (located at 220 52’N latitude and 880 30’E longitude), West Bengal, India with rice (cv. IET 1444). The soil had no history of receiving any pesticide treatment 6 months prior to this study and the field was monocropped with rice only. DCM was applied at the rate of 10 t ha-1. The physico-chemical properties of soil and DCM have been reported (Pal et al., 2005a).
Pencycuron (Monceren 250 SC) obtained from Bayer Crop Science India Ltd., Calcutta was applied at FR (187.5 g a.i. ha-1), 2FR and 10FR. The 1st and 2nd spray of pencycuron were given at 35 and 50 (in 2002) and 34 and 48 (in 2003) day after transplanting, respectively. Five soil samples (0-15 cm depth) were collected from each of the replicated plots under different treatments at 1, 7, 15 and 30 day after the 2nd spray of pencycuron and composited. Pencycuron was quantified using high performance liquid chromatography (Pal et al., 2005a).
Treatments were replicated three times in a Randomized Complete Block Design (RCBD). IRRISTAT statistical package developed by International Rice Research Institute, Philippines was used for the statistical analysis of the data. Bartlett’s homogeneity test was carried out with the two years data. Data observed to be homogeneous for the two years were subjected to combined ANOVA.
Results and Discussion
Pencycuron dissipation in waterlogged rice field soil followed first order kinetics (r2>0.86) and the half-life values were obtained between 4.9 to 5.8 days (Table 1) irrespective of pencycuron application rate, DCM amendment and year of experimentation. The half-lives ranged from 5.5 to 5.8 and 5.1 to 5.7 days in DCM unamended and amended soils respectively in the 1st year while the same were 5.2 to 5.5 and 4.9 to 5.5 days in the 2nd year. Thus there was a statistically significant (p<0.05) decrease (Table 2) in half-lives in the 2nd year. Decrease in half-lives might have resulted from greater root mass and exudates of the crop, which stimulated the proliferation of microorganisms (Bhattacharyya et al., 2005) and/or some kind of adaptation in the degrading microflora (Topp et al., 1997) as the field was monocropped with rice. The effect of pencycuron application rate on the half-life values was statistically nonsignificant. Significant acceleration (p<0.05) of pencycuron dissipation due to addition of DCM resulted either from large microbial biomass in DCM capable of degrading pencycuron faster or from the cometabolic effect of DCM on indigenous soil microbial populations (Pal et al., 2005a, c). The half-life values of pencycuron in soil under field were much lower compared to the laboratory incubated condition.
Table 1: Regression equation, dissipation rate constant (k), correlation coefficient (r2) and half life values of pencycuron in field soil
a Field rate b Decomposed cow manure
Table 2: Effect of application rate and organic matter on half-life value of pencycuron
aLeast significant difference
In same soil under laboratory condition, half-lives of 10.7 to 15.9 days at 60% water holding capacity of soil and 14.8 to 17.3 days under waterlogged condition have been reported in our earlier study (Pal et al., 2005c). The observed decrease in the half-life values of pencycuron might be attributed to the interplay of multiple forces simultaneously at work under actual field condition (Racke et al., 1997).
Acknowledgements
The author is grateful to Department of Agricultural Chemicals, Bidhan Chandra Krishi Viswavidyalaya, India for excellent technical assistance and Bayer Crop Science India Ltd. for sponsoring the research project.
REFERENCES
Bhattacharyya, P., K. Chakrabarti and A. Chakraborty, 2005. Microbial biomass and enzyme activities in submerged rice soil amended with municipal solid waste compost and decomposed cow manure. Chemosphere, 60: 310-318.
Pal, R., K. Chakrabarti, A. Chakraborty and A. Chowdhury, 2005. Pencycuron application to soils: Degradation and effect on microbiological parameters. Chemosphere, 60: 1513-1522.
Pal, R., K. Chakrabarti, A. Chakraborty and A. Chowdhury, 2005. Dissipation of pencycuron in rice plants. J. Zhejiang Univ. Sci., 6: 756-758.
Pal, R., K. Chakrabarti, A. Chakraborty and A. Chowdhury, 2005. Pencycuron dissipation in soil: Effect of application rate and soil conditions. Pest Manage. Sci., 61: 1220-1223.
Perucci, P., C. Vischetti and F. Battistoni, 1999. Rimsulfuron in a silty clay loam soil: Effects upon microbiological and biochemical properties under varying microcosm conditions. Soil Bio. Biochem., 31: 195-204.
Racke, K.D., M.W. Skidmore, D.J. Hamilton, J.B. Unsworth, J. Miyamoto and S.J. Cohen, 1997. Pesticide fate in tropical soils. Pure Applied Chem., 69: 1349-1371.
Tomlin, C.D.S., 1997. Pencycuron: The Pesticide Manual. 11th Edn., British Crop Protection Council, UK., pp: 935-937.
Topp, E., T. Vallaeys and G. Soulas, 1997. Pesticides: Microbial Degradation and Effects on Microorganisms. In: Modern Soil Microbiology, Van Elsas, J.D., J.T. Trevors and E.M.H. Wellington (Eds.). Mercel Dekker Inc., New York, USA., pp: 547-575.
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Fate of the Dicamba in the Environment
Soil
Dicamba will persist in the soil for up to 3 months, or longer, in the soil. Breakdown rates in the soil are primarily due to volitalization losses from the soil, and microbial degradation in warm, moist soils. As such it is an effective soil-applied herbicide for weed control after the spring is over. Dicamba is highly mobile in soils and can leach readily in the soil, especially in sandy soils. It can injure plant roots in these lighter soils. Little soil adsorption of dicamba to the soil colloidal fraction occurs. This adsorption is a function of soil pH: adsorption increases with a decrease in soil pH, decreased adsorption with calcareous soils.
Air
One of the problems encountered with the use of dicamba is volatility leading to drift of the herbicide in the air. It is more volatile than 2,4-D and can cause injury in more instances than that herbicide on adjacent susceptible plants. Often dicamba drift can travel farther than 2,4-D also.
Toxicology
Dicamba is excreted by animals with relatively rapid uptake, with little metabolism occuring to the parent molecule.
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2011年10月8日星期六
The Secondary Effects of Pencycuron on the Formation of Giant Protoplasts and the Lipid Peroxidation of Rhizoctonia solani AG4
The secondary effects of pencycuron on cell membrane of Rhizoctonia solani AG4 were investigated by the observation of giant protoplast formation and lipid per¬oxidaiton. Compared to protoplasts initially produced from the strains, protoplasts of R. solani R-C (sensitive strain) and Rh-131 (non-sensitive strain) increased in their size by 2.0-3.5 times 12 h after incubation in potato-dextrose broth containing novozyme (7 mg/ml) and β-glucuronidase (60 µl/ml) with 0.6 M mannitol (pH 5.2). The increase of protoplast size in R-C was slightly inhibited from 13.8 µm without pencycuron to 10.3 µm with 1.0 µg/ml of pencycuron. However, the size of giant protoplast of Rh-131 was not affected by the pencycuron treatment. Both strains R-C and Rh-131 did not exhibit the lipid peroxidation 12 h after the application of 1.0 µg/ml pencycuron. The remarkable peroxidation of membrane lipid was observed only in R-C 24 h after pencycuron application, but not in Rh¬131. Although the inhibition of giant protoplast forma¬tion and the membrane lipid peroxidation were observed only in the sensitive strain R-C by pencycuron, it is diffi¬cult to conclude that these are the primary mechanism of pencycuron. The mild activity of pencycuron on the inhibition of giant protoplast formation and late mem¬brane lipid peroxidation in the fungicide-sensitive strain did not coincide with the dramatic activity of pencycu¬ron in R. solani. Therefore, our results suggest that inhi¬bition of giant protoplast formation and membrane lipid peroxidation is the secondary effect of pencycuron.
Physiology & Metabolism of Dicamba
Mode of Action & Lethality
The mode of action of dicamba is probably similar to that of the phenoxy carboxylic acids. Rapid, abnormal, cell growth then leads to the disruption of the phloem system and normal auxin balance in the plant. As with the phenoxy carboxylic acids, these herbicides act by stimulating abnormal cell growth in meristematic cells. This can result in the blockage of phloem vascular tissue. Extensive destruction of cambial, phloem cells near meristems occurs within days of treatment. The plant is killed by starvation resulting form an inability to translocate needed energy in the phloem.
Uptake and Movement of Dicamba in Plants
Dicamba is rapidly absorbed by plant root and shoot tissue. Dicamba translocates readily in the xylem and phloem. Dicamba taken up by plant roots is translocated mostly in the xylem initially, but over a longer time it moves to areas of high metabolic activity.
Basis of Selective Toxic Action between Susceptible & Resistant Species
Selective dicamba toxicity amongst plant species appears to be a function of uptake, distribution in the plant, and metabolism. In some tolerant species, translocation is limited to the xylem. Tolerant species metabolically degrade dicamba rapidly. The primary degradation pathway is by metabolism of the herbicide (ring hydroxylation followed by very rapid glucoside conjugation).
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The mode of action of dicamba is probably similar to that of the phenoxy carboxylic acids. Rapid, abnormal, cell growth then leads to the disruption of the phloem system and normal auxin balance in the plant. As with the phenoxy carboxylic acids, these herbicides act by stimulating abnormal cell growth in meristematic cells. This can result in the blockage of phloem vascular tissue. Extensive destruction of cambial, phloem cells near meristems occurs within days of treatment. The plant is killed by starvation resulting form an inability to translocate needed energy in the phloem.
Uptake and Movement of Dicamba in Plants
Dicamba is rapidly absorbed by plant root and shoot tissue. Dicamba translocates readily in the xylem and phloem. Dicamba taken up by plant roots is translocated mostly in the xylem initially, but over a longer time it moves to areas of high metabolic activity.
Basis of Selective Toxic Action between Susceptible & Resistant Species
Selective dicamba toxicity amongst plant species appears to be a function of uptake, distribution in the plant, and metabolism. In some tolerant species, translocation is limited to the xylem. Tolerant species metabolically degrade dicamba rapidly. The primary degradation pathway is by metabolism of the herbicide (ring hydroxylation followed by very rapid glucoside conjugation).
Yangzhou pioneer chemical CO.,LTD
2011年10月7日星期五
Combination of pencycuron and Pseudomonas fluorescens strain 2-79 for integrated control of rhizoctonia root rot and take-all of spring wheat
Pencycuron (tradename Monceren, a fungicide developed specifically to control Rhizoctonia) was evaluated for in vitro growth inhibition of wheat pathogenic Rhizoctonia spp., Gaeumannomyces graminis var. tritici and Pythium spp., and for control of wheat root diseases in greenhouse trials. In the greenhouse, pencycuron inhibited binucleate Rhizoctonia, R. oryzae, or R. solani in vitro and reduced Rhizoctonia root rot. Pencycuron also inhibited G. graminis var. tritici strains in vitro and slightly reduced take-all disease in the greenhouse. Moreover, pencycuron seed treatment protected plants against a disease mixture of Rhizoctonia root rot and take-all. Pythium spp. were not inhibited by pencycuron in vitro. Pencycuron did not adversely affect seedling emergence, nor did it inhibit rhizosphere colonisation by Pseudomonas fluorescens biocontrol strain 2-79. Combined application of the fungicide and strain 2-79 to seed was more effective than either treatment alone for controlling disease.
Differences in Injury due to Dicamba and 2,4-D
It is hard, if not impossible, to definitely differentiate between injury caused by these two similar herbicides. There are several keys that often can be helpful though.
1. Dicamba translocates more completely throughout a plant and better control of woody and brushy species can help: these species will be injured more by dicamba than 2,4-D.
2. Another difference is the tendency of dicamba to flatten and twist monocot leaves just after treatment, a symptom not encountered as much with 2,4-D.
3. Dicamba can drift in the air to greater distances than does 2,4-D.
4. Dicamba injury often will develop over a longer period than 2,4-D: dicamba is slower acting.
5. 2,4-D often will cause slightly more corn stalk injury under the same conditions than that caused by dicamba.
6. Dicamba has a longer residual effect in the soil than that from 2,4-D.
7. Dicamba costs more than 2,4-D, look for thrifty farmers using 2,4-D.
8. Dicamba may also act so quickly that it doesn"t form the "strap-shaped" leaves, narrow and puckered, that 2,4-D does. Dicamba injured leaves instead are shorter than those with 2,4-D.
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1. Dicamba translocates more completely throughout a plant and better control of woody and brushy species can help: these species will be injured more by dicamba than 2,4-D.
2. Another difference is the tendency of dicamba to flatten and twist monocot leaves just after treatment, a symptom not encountered as much with 2,4-D.
3. Dicamba can drift in the air to greater distances than does 2,4-D.
4. Dicamba injury often will develop over a longer period than 2,4-D: dicamba is slower acting.
5. 2,4-D often will cause slightly more corn stalk injury under the same conditions than that caused by dicamba.
6. Dicamba has a longer residual effect in the soil than that from 2,4-D.
7. Dicamba costs more than 2,4-D, look for thrifty farmers using 2,4-D.
8. Dicamba may also act so quickly that it doesn"t form the "strap-shaped" leaves, narrow and puckered, that 2,4-D does. Dicamba injured leaves instead are shorter than those with 2,4-D.
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