Influence of soil moisture on the formation of dressing zones and uptake of imidacloprid after seed treatment of winter wheat
1992
Stein-Doenecke, U. (Kernforschungsanlage Juelich G.m.b.H. (Germany). Forschungszentrum. Inst. fuer Radioagronomie) | Fuehr, F. | Wienecke, J. | Hartwig, J. | Leicht, W.
Winter wheat seed was treated with (pyridinyl-(14)C-methylene)- imidacloprid and with non-radiolabelled active ingredient at doses of 100 g a.i./dt. The mean doses per seed were 50.4 amd 52.7 mig imidacloprid respectively. Sowing took place on 20.11.90, in four 1 square-metre seed boxes topped with grey-brown podzolic soil. The radioactive and non-radioactive caryopses were so laid out as to exclude overlapping of radioactive treatment zones. The soil moisture contents, 30, 40, and 50% WHCmax, were maintained over the duration of the study by protection of the boxes from natural precipitation and by calculated watering. The uptake of radioactivity into the sprouting wheat at 40% WHC((max)) showed a continuous increase, from 1.1% of the applied activity at the 1-leaf stage to 18.8% at full maturity. The distribution of the (14)C-labelled substances taken up was typical of xylem-mobile active ingredients. At each growth stage there was a concentration gradient between the highest concentration in the oldest leaf and lowest in the youngest. The a.i. equivalent concentrations in the leaves ranged from 80 mg to 40 mig per kg fresh material. At full maturity the concentrations in the grains (0.04 mg a.i. equivalents/kg dry mass) were considerably lower than those in the straw and chaff (1.24-1.93 mg/kg dry mass). At the investigated growth stages (start of tillering and start and end of the shooting phase: respectively 111, 153, and 195 days after sowing) the influence of an increasing soil moisture content manifested itself by an increased loss of radioactivity from the caryopsis with clearly reduced uptake into the plant
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