Pencycuron
[1-(4-chlorobenzyl)-1-cyclopentyl-3-phenylurea], a relatively new non-systemic
protective fungicide for controlling sheath blight (Rhizoctonia solani) of rice
(Sylvanie and Cornis, 1989; Tomlin, 1997), is expected to be used widely in
agricultural production particularly in Asia. However, information on the
dissipation pattern of pencycuron in rice plant is lacking. Little
information on the environmental fate of pencycuron has been published although
there were some published studies on rice sheath blight fungus (Mithrasena et
al., 1989; Wickramasinghe and Mithrasena, 1989; van Eeckhout et al., 1991;
Osada, 1993).
Rice is now the major cereal crop in the Indian subcontinent. The introduction of improved technology for present day rice production invites insect pests and diseases. Among different rice varieties commercially cultivated in West Bengal of India, most are highly susceptible to sheath blight and suffer considerable loss. Among many classes of fungicides, pencycuron (Monceren) is now going to be introduced to the Indian subcontinent by Bayer Crop Science, India. As information on the residue and dissipation of pencycuron in rice plant under cultivation under our agro-climatic conditions is not available, systematic study on the residue and dissipation of pencycuron in rice plant grown under our agro-climatic conditions should be conducted.
Field experiments on rice (cv IET 1444) were conducted for three consecutive years in the June to October wet seasons of 2001, 2002 and 2003 at the Agriculture Experimental Farm, Bidhan Chandra Krishi Viswavidyalaya, Mohanpur (located at 22°52′ N, 88°30′ E, 1.3 m above mean sea level), West Bengal, India. The climate of the region is sub-humid with average total annual precipitation of 1300 mm, and maximum rainfall in June to September. The maximum temperature of the study zone reaches to about 38.6 °C in May and the minimum temperature reaches to 11.3 °C in January. Warm conditions (35.7 °C) and high humidity (94%) prevail during the rainy season.
The land was prepared by puddling with the help of a power tiller. Decomposed cow manure (DCM) applied at 10 t/ha seven days before rice transplantation contained dry weigh 14.0% organic C and 1.36% total N at pH 7.4. All the plots received a recommended dose of 60:30:30 N, P and K ha1 in the form of urea, single super phosphate and muriate of potash. The half dose of N and full dose of P and K were applied as basal fertilizers. The remaining half dose of N was applied 21 d after rice seeding transplantation. High yielding rice variety IET-1444 seedings (23, 24 and 27 d old in the year 2001, 2002 and 2003, respectively) were transplanted in rows 20 cm apart and 15 cm between hills. Each hill contained three seedlings. Pencycuron 250 SC obtained from Bayer Crop Science India Ltd. was applied at recommended field dose (187.5 g a.i./ha) and double recommended dose. The 1st and 2nd spray of pencycuron were given at 33 and 49 (in the year 2001), 35 and 50 (in the year 2002) and 34 and 48 (in the year 2003) day after transplantation respectively. Treatments were replicated three times in a randomized complete block design.
Pencycuron was quantified using high performance liquid chromatography (HPLC 1050 Hewlett Packard equipped with UV detector and 3392A integrator). For recovery studies, rice plants were fortified with acetone solution of pencycuron to obtain concentrations corresponding to different doses. The samples were immediately extracted three times with 100 ml of acetone on an electric blender for 5 min. After centrifugation at 3000 r/min for 10 min, the extracts were combined and pencycuron was partitioned in CHCl3 ((100+50+50) ml). The CHCl3 layer was evaporated to dryness, rinsed with HPLC grade methanol and filtered (0.2 μm) for direct HPLC analysis. Pencycuron was separated on an Intersil 150 mm×4.6 mm ODS 2, 5 μm (RPC18 column) using a mobile phase of methanol and water (90:10) at a flow rate of 1 ml/min and column temperature at 40 °C. Quantification was performed against pencycuron standard at a wavelength of 240 nm. Under this condition the retention time of pencycuron was 3.2 min, the limit of detection was 0.01 mg and the sensitivity of the method was 0.005 mg/kg. The average recovery was 90.0%~93.4% for pencycuron with relative standard deviations ranging from 2.5~3.0. Determination of pencycuron residues in the treated samples was carried out as per the recovery study.
The initial deposit of pencycuron after two hours spraying was found to be 0.0190~0.0204 and 0.0386~0.0440 mg/kg irrespective of the seasons for the treatments T1 and T2 respectively. The loss of residues over a period of time showed steady dissipation from 67.62%~95.10 % within 7 d. The residue level fell below detectable limit on the10th day for T1 and 15th day for T2.
The dissipation of pencycuron residue followed first order reaction kinetics in all the doses as a straight line was obtained in each case when log values of the residue were plotted against different time intervals. From this study it appeared that the rate of dissipation was independent of initial deposit and that the half-life of
pencycuron varied from 1.57~2.77 d irrespective of the seasons
and application rate.
For the untreated control, no residues of pencycuron were detected irrespective of the seasons and in grain, husk and straw at harvest. During the experiment no phytotoxicity was observed for any of the treatments. The half-lives of pencycuron in rice were observed to be short and should be of no concern regarding contamination of the food chain and environment.
Rice is now the major cereal crop in the Indian subcontinent. The introduction of improved technology for present day rice production invites insect pests and diseases. Among different rice varieties commercially cultivated in West Bengal of India, most are highly susceptible to sheath blight and suffer considerable loss. Among many classes of fungicides, pencycuron (Monceren) is now going to be introduced to the Indian subcontinent by Bayer Crop Science, India. As information on the residue and dissipation of pencycuron in rice plant under cultivation under our agro-climatic conditions is not available, systematic study on the residue and dissipation of pencycuron in rice plant grown under our agro-climatic conditions should be conducted.
Field experiments on rice (cv IET 1444) were conducted for three consecutive years in the June to October wet seasons of 2001, 2002 and 2003 at the Agriculture Experimental Farm, Bidhan Chandra Krishi Viswavidyalaya, Mohanpur (located at 22°52′ N, 88°30′ E, 1.3 m above mean sea level), West Bengal, India. The climate of the region is sub-humid with average total annual precipitation of 1300 mm, and maximum rainfall in June to September. The maximum temperature of the study zone reaches to about 38.6 °C in May and the minimum temperature reaches to 11.3 °C in January. Warm conditions (35.7 °C) and high humidity (94%) prevail during the rainy season.
The land was prepared by puddling with the help of a power tiller. Decomposed cow manure (DCM) applied at 10 t/ha seven days before rice transplantation contained dry weigh 14.0% organic C and 1.36% total N at pH 7.4. All the plots received a recommended dose of 60:30:30 N, P and K ha1 in the form of urea, single super phosphate and muriate of potash. The half dose of N and full dose of P and K were applied as basal fertilizers. The remaining half dose of N was applied 21 d after rice seeding transplantation. High yielding rice variety IET-1444 seedings (23, 24 and 27 d old in the year 2001, 2002 and 2003, respectively) were transplanted in rows 20 cm apart and 15 cm between hills. Each hill contained three seedlings. Pencycuron 250 SC obtained from Bayer Crop Science India Ltd. was applied at recommended field dose (187.5 g a.i./ha) and double recommended dose. The 1st and 2nd spray of pencycuron were given at 33 and 49 (in the year 2001), 35 and 50 (in the year 2002) and 34 and 48 (in the year 2003) day after transplantation respectively. Treatments were replicated three times in a randomized complete block design.
Pencycuron was quantified using high performance liquid chromatography (HPLC 1050 Hewlett Packard equipped with UV detector and 3392A integrator). For recovery studies, rice plants were fortified with acetone solution of pencycuron to obtain concentrations corresponding to different doses. The samples were immediately extracted three times with 100 ml of acetone on an electric blender for 5 min. After centrifugation at 3000 r/min for 10 min, the extracts were combined and pencycuron was partitioned in CHCl3 ((100+50+50) ml). The CHCl3 layer was evaporated to dryness, rinsed with HPLC grade methanol and filtered (0.2 μm) for direct HPLC analysis. Pencycuron was separated on an Intersil 150 mm×4.6 mm ODS 2, 5 μm (RPC18 column) using a mobile phase of methanol and water (90:10) at a flow rate of 1 ml/min and column temperature at 40 °C. Quantification was performed against pencycuron standard at a wavelength of 240 nm. Under this condition the retention time of pencycuron was 3.2 min, the limit of detection was 0.01 mg and the sensitivity of the method was 0.005 mg/kg. The average recovery was 90.0%~93.4% for pencycuron with relative standard deviations ranging from 2.5~3.0. Determination of pencycuron residues in the treated samples was carried out as per the recovery study.
The initial deposit of pencycuron after two hours spraying was found to be 0.0190~0.0204 and 0.0386~0.0440 mg/kg irrespective of the seasons for the treatments T1 and T2 respectively. The loss of residues over a period of time showed steady dissipation from 67.62%~95.10 % within 7 d. The residue level fell below detectable limit on the10th day for T1 and 15th day for T2.
The dissipation of pencycuron residue followed first order reaction kinetics in all the doses as a straight line was obtained in each case when log values of the residue were plotted against different time intervals. From this study it appeared that the rate of dissipation was independent of initial deposit and that the half-life of
pencycuron varied from 1.57~2.77 d irrespective of the seasons
and application rate.For the untreated control, no residues of pencycuron were detected irrespective of the seasons and in grain, husk and straw at harvest. During the experiment no phytotoxicity was observed for any of the treatments. The half-lives of pencycuron in rice were observed to be short and should be of no concern regarding contamination of the food chain and environment.
Yangzhou pioneer chemical CO.,LTD
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