I was told not to eat vegetables that had been sprayed with a systemic insecticide not labeled for use on vegetables? Why?
Systemic insecticides are chemicals that can be absorbed through the roots or leaves of plants and translocated in the sap in sufficient amounts to kill insects and related pests feeding on the plants. The chemicals spread throughout the plant as it grows, and don't wash off in rainy weather as other pesticides do. Consequently, if you eat the fruit of the plant sprayed with systemic pesticide, you could be consuming various amounts of the pesticide, which could be harmful.
Product labels restrict systemic pesticide use and it is true that most are not labelled for use on fruit and vegetables. However, certain systemic insecticide products are available on the market that are labeled for use on fruit trees. Caution should still be exercised when using these products as many are limited to only one application per year and from an environmental standpoint, it is important to know that these systemic pesticides will harm or kill pollinators (bees).
When using any pesticide, practice strict adherence to the label directions. Moreover, these labels are legal documents, meaning that it is illegal to use these pesticides in a manner contrary to the directions (i.e. on an unnamed crop).