Comparison of pesticide residue levels in headed lettuce growing in open fields and greenhouses

To evaluate the influence of growing conditions on the pesticide residue in lettuce heads, we investigated the residue levels in open field and greenhouse conditions. A clear difference between the two growing conditions was observed for dinotefuran applied to the planting hole; the residue levels in the lettuce heads from the greenhouses were almost as high as those in the field samples. In contrast, no clear difference between the two growing conditions was observed for the other three pesticides applied to the foliage. The size reduction process for sample preparation also affected the variation in this residue data; the ranges between two size-reduced samples of dinotefuran were narrower than the values of the other three pesticides. Those results are part of the complex factors affecting the pesticide residue levels in lettuce heads in different growing conditions and with different types of application.