Articles
Decrease in fungicide concentrations in recirculated citrus postharvest treatment suspensions by interaction with soil, fruit, and other substances –
a first report
Article number
1451_6
Pages
35 – 48
Language
English
Abstract
Currently, postharvest treatments for decay control of citrus fruits are applied mostly by high-volume aqueous recirculated suspensions in the form of drenchers, flooders, and dip tanks.
However, despite the use of pre-programmed automatic dosing systems, when the suspensions are reused different disturbances occur that alter the concentration of the fungicides applied, and that cause the concentration to deviate from the optimal working value, both by excess, which can generate fungicide residues higher than maximum residue levels (MRL) or what is required by retailers, but generally below the target, leading to poor decay control and the buildup of fungicide resistance.
Among the main phenomena that can lead to a reduction in fungicide concentration are their absorption by soil particles carried from the groves by the fruit, or the degradation by the action of organic and inorganic matter carried by fruit and soil, and/or by foreign substances i.e., products applied in the groves, etc.
In the present work, we show for the first time the results of absorption and degradation of imazalil, pyrimethanil, ortho-phenylphenol and potassium sorbate in industrial treatment suspensions of citrus drenchers, flooders and dip tanks from an important number of packinghouses, as well as data on residue uptake by different types of citrus cultivars and fruit maturity at harvest.
The behaviour of industrial treatment suspensions was evaluated as a function of time, amount of fruit treated, physicochemical characteristics and geographical origin.
Significant and highly variable degradation rates were observed for imazalil (30-100% in 24 h), which could not be correlated with any sample parameter, while pyrimethanil, ortho-phenylphenol and sorbate showed lower degradation rates.
In terms of absorption, very variable percentages were also observed (5-95%), being on average higher for pyrimethanil, intermediate for imazalil and very low for sorbate and ortho-phenylphenol.
These results indicate that, due to the changing and unpredictable nature of these alterations, it is difficult to find a universal solution to maintain constant concentrations in the high-volume recirculated treatment suspensions, and it is necessary to have an online monitoring and control system.
However, despite the use of pre-programmed automatic dosing systems, when the suspensions are reused different disturbances occur that alter the concentration of the fungicides applied, and that cause the concentration to deviate from the optimal working value, both by excess, which can generate fungicide residues higher than maximum residue levels (MRL) or what is required by retailers, but generally below the target, leading to poor decay control and the buildup of fungicide resistance.
Among the main phenomena that can lead to a reduction in fungicide concentration are their absorption by soil particles carried from the groves by the fruit, or the degradation by the action of organic and inorganic matter carried by fruit and soil, and/or by foreign substances i.e., products applied in the groves, etc.
In the present work, we show for the first time the results of absorption and degradation of imazalil, pyrimethanil, ortho-phenylphenol and potassium sorbate in industrial treatment suspensions of citrus drenchers, flooders and dip tanks from an important number of packinghouses, as well as data on residue uptake by different types of citrus cultivars and fruit maturity at harvest.
The behaviour of industrial treatment suspensions was evaluated as a function of time, amount of fruit treated, physicochemical characteristics and geographical origin.
Significant and highly variable degradation rates were observed for imazalil (30-100% in 24 h), which could not be correlated with any sample parameter, while pyrimethanil, ortho-phenylphenol and sorbate showed lower degradation rates.
In terms of absorption, very variable percentages were also observed (5-95%), being on average higher for pyrimethanil, intermediate for imazalil and very low for sorbate and ortho-phenylphenol.
These results indicate that, due to the changing and unpredictable nature of these alterations, it is difficult to find a universal solution to maintain constant concentrations in the high-volume recirculated treatment suspensions, and it is necessary to have an online monitoring and control system.
Authors
J. Parra, M. Isnardo, B. Orihuel-Iranzo
Keywords
citrus decay control, fungicide sub-lethal concentration, fungicide degradation, fungicide soil absorption, imazalil, pyrimethanil, ortho-phenylphenol, potassium sorbate
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