| heal.abstract |
The application of suitable systemic pesticides via the nutrient solution in substrate-grown crops provides an environmentally friendly alternative to foliar sprays, when the fertigation effluents are collected and reused, since both the leaching of residues into groundwater and the exposure of workers to spray drift are avoided. However, the limited knowledge about the fate of plant protecting substances after application in substrate crops is the main factor limiting a broad adaptation of this alternative method. This paper reports some preliminary results regarding the fate of some efficient, low-toxicity insecticides, specifically cyromazine, imidacloprid, thiacloprid, and thiamethoxam, in the fertigation effluents and in plant tissues following application via the root system at an early plant growth stage in crops grown in closed-cycle soilless cultivation systems. After a single application, the fate of the selected insecticides was traced by regularly collecting samples of nutrient solution, substrate, roots, leaves, and fruits over a period of several weeks and analysing by HPLC. Cyromazine and imidacloprid were applied via the recycled nutrient solution in a bean crop grown on pumice. The results indicated that cyromazine may persist for relatively long periods in both the recycled nutrient solution and the plant tissues, but the translocation to fruits remain at low levels. The application of imidacloprid 20- 25 days before the pods of bean reach marketable size provided long-term protection against pests by maintaining the pesticide residues in the edible pods far below the MRL. The insecticides thiacloprid and thiamethoxam were applied in closed-cycle cultivations of tomato grown on rockwool and perlite, respectively. The persistence of thiacloprid and thiamethoxam in the recycled nutrient solution was even shorter than that of imidacloprid. Relatively high amounts of thiacloprid were translocated to leaves and fruits of tomato, while the amounts of thiamethoxam absorbed by tomato were fairly low and the residues in the plant tissues tended to dissipate much more rapidly than those of any other of the tested insecticides. |
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