| Abstrakt: |
Tebufenozide (RH‐5992, MIMIC®) [N'‐f‐butyl‐N'‐(3,5‐dimethylbenzoyl)‐N‐(4‐ethyl‐benzoyl) hydrazine] has the potential for use in spruce budworm (Choristoneura fumiferana Clem.) control in Canadian forestry. Its persistence and fate in different forestry components after its aerial application were investigated. An emulsion suspension of MIMIC (containing a tracer dye) was applied twice, each time at the rate of 70 g of active ingredient (Al)/ha over a mixed‐wood forest near Longlac, Ontario, Canada, during 1994. Droplet density (droplets/cm2) and volume median diameter were determined on spruce needles [Picea glauca (Moench) Voss] after the 1st application, and the values averaged to 3.8 and 60 μm respectively. Droplet density, volume median diameter and deposit density (g Al/ha) determined on collection units near the pond site, were higher for the 1st application than for the 2nd application. In contrast, the corresponding values for the stream site were lower for the 1st application than for the 2nd application. The highest concentration of tebufenozide (μg/g wet wt) in soil was 0.101 for the 1st application, which was slightly lower than the value (0.116) obtained for the 2nd application. The corresponding values in litter were higher, 0.118 and 0.144 respectively. The residues decreased gradually with time and persisted until the last sampling day (87 d post‐spray). The DT50 (time required for 50 % of the initial deposit to dissipate) values were 42.2 d for soil and 80.0 d for litter, indicating the potential for overwintering of tebufenozide residues in these two matrices. The highest concentrations (ng/g fresh wt) of the chemical in spruce needles 1 h after the 1st and 2nd applications were 1.68 and 3.01 respectively, and for spruce shoots (current year growth) 1.06 and 2.08 respectively. The residues in spruce shoots disappeared faster than those in needles, although the chemical persisted in both matrices up to 87 d post‐spray, indicating similar overwintering potential as seen in soil and litter. The DT50 values for the needles and shoots were 44.3 d and 18.4 d, respectively. Higher initial deposits (μg/g fresh wt, 5.18 for 1st application and 5.51 for the 2nd application) were found on balsam poplar (Populus balsamifera L.) leaves than on spruce needles. The DT50 value (58.7 d) was also higher. The stream site received very low deposits during the 1st spray. The maximum 1 h post‐spray concentrations (μg/L) in the stream (2nd application) and pond waters (1st and 2nd applications) were 1.32, 5.31 and 1.26 respectively. Concentrations decreased rapidly in both sites after spray, giving an average DT50 value of 1.6 d. The initial 1‐h concentrations (μg/g wet wt) of the chemical in stream and pond sediments were low and ranged from 0.005 to 0.010. No residues were found in the stream or pond sediments after 4 and 12 d post‐spray (2nd application), respectively. Although the residues were transient, the data indicated a tendency for the sediment to act as a sink by adsorbing the chemical from the surrounding waters. After the second application, stream moss (Drepanoclàdus) gradually accumulated the chemical from an initial low concentration (μg/g, wet wt) of 0.072 (stream) to a peak level of 0.232 at 3 d post‐spray. Similarly, concentrations in pond moss increased from 0.120 (at 1 h) to 0.210 on 1 d post‐spray, indicating that both stream and pond moss acted as efficient sinks for the chemical. Residues declined from peak levels to non‐detectable levels in the stream moss after 38 d post‐application; however, the material persisted at detectable levels (0.015 μg/g) in pond moss beyond the 87 d sampling period. The foliage of marsh marigold (Caltha palustris) acted as a good receptor for the spray droplets. The initial concentrations (μg/g wet wt) of tebufenozide in stream (2nd application) and pond (1st and 2nd applications) samples were 0.896, 4.147 and 1.896 respectively. The residue levels at both sites decreased with time and the DT50 values ranged from 2.0 to 3.9 d (average value of 2.7 d). No residues were found in marigold foliage after 24 d post‐application. Transient but quantifiable levels of the chemical in the range of 0.069 to 0.13 μg/g (wet wt) were found in marigold roots, showing tendencies of bioconcentration. However, the residues declined to below the quantification level within 4 d (stream) and 12 d (pond) after application. Results of the study showed that a consortia of environmental factors (physical, chemical and metabolic) exerted influence to reduce both the duration and concentrations of tebufenozide in the forestry matrices. [ABSTRACT FROM AUTHOR] |
