The metabolism of teflubenzuron was investigated in apples, potatoes, cotton and spinach.
Apples. Schlüter (1987a) treated selected parts of young apple trees three times with formulated [U-aniline-14C]teflubenzuron according to the spraying schedule to be applied in agricultural practice: treatments at 3-week intervals with a 3-6 week PHI. The surfaces of the fruits and leaves were covered with droplets of the application mixture. The concentration of the active ingredient was 0.2 mg/ml (two to four times that used in agricultural practice, 0.05-0.1 mg/ml). Treated apples were sampled at intervals as well as at normal harvest, and treated and untreated leaves and untreated apples only at harvest. The radioactive residues in treated leaves and apples consisted almost exclusively of unchanged teflubenzuron: 99% and 98% respectively.
It was concluded that teflubenzuron does not penetrate into the fruits or leaves if it is sprayed on apple trees, with no systemic transport and no metabolism within the plants.
Potatoes. Schlüter (1987b) studied metabolism and kinetics of [14C]teflubenzuron (uniformly labelled in the aniline ring) in potato plants. The tops of the plants as well as the soil surfaces of a potato plot were separately treated four times according to the spraying schedule to be used in agricultural practice (treatments at about 2-week intervals, the last treatment at the beginning of flowering). Some of the plants were treated by spraying the leaves only (the soil was covered with plastic foil and cellulose tissues), and in part of the plot the application mixture was applied to the soil with no leaf treatment. The application rate of the active ingredient was 90 g ai/ha (3 times the highest rate recommended in practice of 10-30 g ai/ha). Treated and untreated tubers and tops were sampled at the growing stage and at normal harvest.
At the end of the test period (63 days after the first treatment), 99.8% of the total radioactivity was extractable from the treated leaves and could be identified as the unchanged parent compound. No significant amounts of radioactive residues were found in the tubers of leaf-treated plants, but trace amounts were detectable in the tubers sampled after soil treatment. After peeling the tubers, mean residues of 0.009 mg/kg were found in the peel, which corresponded to 0.03% of the total radioactivity applied. A total residue of 0.002 mg/kg in unpeeled tubers can be calculated.
It was concluded that teflubenzuron does not penetrate into leaves or stems if it is sprayed on to the aerial parts of potato plants. No translocation or metabolism occurs in the plants.
Cotton. Cotton plants (Gossypium hirsutum) were repeatedly treated with formulated teflubenzuron according to the recommendations. Six unlabelled treatments at 81 g ai/ha were followed by two applications of 156 g ai/ha of formulated [U-aniline-14C]teflubenzuron (Schwalbe-Fehl et al., 1986). Various plant parts and soil were sampled periodically until harvest. The concentrations of 14C in the samples at harvest were as follows.
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Soil: |
0.05 mg ai equivalent/g air dried soil (0-5 cm) |
|
Leaves: |
6.4 mg ai equivalent/g fresh sample |
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Stems: |
0.5 mg ai equivalent/g fresh sample |
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Capsule walls: |
0.4-0.9 mg ai equivalent/g fresh sample |
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Seed hairs: |
0.02-1.5 mg ai equivalent/g fresh sample |
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Seeds: |
0.005-0.011 mg ai equivalent/g fresh sample |
Significant residues were found only in those plant parts which were directly hit by the radiolabelled spray. The test substance was not translocated to closed cotton fruits or seeds. The radioactive residues were almost quantitatively extractable (93-98% of the total radioactivity). More than 99% of the extractable radioactivity was from the unchanged parent compound.
Spinach. Spinach plants were subjected to one run-off spray treatment with 20 ml of a 0.18% spray-wash containing 247 mg/kg [14C]teflubenzuron, which corresponds to an application rate of 60 g ai/ha (Schlüter, 1985b).
The treated plants showed 6.9, 1.01, and 0.7 mg/kg total radioactive residues at 0, 8 and 15 days after treatment respectively. Almost all the residue could be removed from the plants by a surface rinse at all sampling times (at day 0 99%, day 8 99.1%, and day 15 99.2% of the corresponding total radioactive residue).
The remaining 0.8-1.0% was extractable after homogenization of the plants. TLC showed that most of the radioactive residue consisted of unchanged teflubenzuron, which amounted to 94.8% of the total radioactive residue on day 0, 91.7% on day 8 and 77.1% on day 15.
The sum of the degradation products reached 22.9% at day 15. No major product was found. The fact that the radioactivity was almost completely removed by surface rinsing indicates the absence of metabolic degradation. It is more likely that teflubenzuron is photolytically degraded when applied to the plant surface.
