Marie-Paule Charnay

Degradation of formulated and unformulated triticonazole fungicide in soil : effect of application rate

Laboratory incubation studies were conducted to evaluate the influence of commercial formulation adjuvants and application rate over a range of 0.2–80 mg kg−1 on the dissipation of 14C-triticonazole systemic fungicide in a loamy clay soil, at 22 and 28°C, and 80% of water field capacity. Measurement of the balance of the 14C-residues after incubation at 22°C showed an increased resistance to desorption with time, as apparent desorption Kapp increased from 2 to 10 l kg−1 in a 133 d period. Decreased extractability of the residues with incubation time and formation of bound residues up to 20% showed that the overall availability of triticonazole decreased with incubation time. The addition of diluted doses of formulation adjuvants did not significantly affect the degradation and binding of the active ingredient. Mineralization of triticonazole was slow, with a high activation energy of 130 kJ mol−1. The persistence of triticonazole increased with application rate, as the first-order mineralization rates at 28°C decreased from 2×10−3 to 0.7×10−3 d−1 with amount applied increasing from 0.2 to 80 mg kg−1. However, the absolute amount of triticonazole mineralized increased with increasing concentration in the soil solution, and the slow mineralization was attributed to limited availability in the soil solution due to high sorption.

Influence of soil type and water content on release of triticonazole from coated maize seed

The release of [14C]triticonazole from coated maize seeds into soil, and its incorporation in maize, were studied under laboratory conditions over seven days in two soils at two different water contents (equivalent to a matrix potential of −3 kPa and −1580 kPa). The behaviour of a commercial coating formulation was compared to that of the same formulation supplemented with a pellicle to improve coated seed handling. Triticonazole released into soil, remaining in the integument and incorporated in different parts of the plant (stem, root, albumen) was measured. The triticonazole released into the soil corresponded to 25% of the initial applied amount on the seed under the best conditions (sandy soil, matrix potential of −3 kPa, set without pellicle). In these conditions, 13% of applied triticonazole was incorporated into roots and stems after seven days. The presence of an additional pellicle to improve the coating decreased the quantity of triticonazole released into soil and consequently the quantity of triticonazole incorporated into the plant. In all cases, the diffusion of triticonazole from the seed to the soil was not limited by the water solubility of triticonazole. Instead, the sorption of triticonazole on soil appears to be the key process governing its fate in soil. © 2000 Society of Chemical Industry