Genetically modified foods are crops where genes from bacteria or viruses are forced into their DNA. The two main categories are those that are engineered not to die when sprayed with a toxic herbicide and those that produce their own toxic insecticide.A problem arises in the former case because crops can be doused in herbicides and even thorough washing may not be effective. And in the latter case no amount of washing, no matter how thorough, can eliminate the insecticide because it’s bred right into the plant.