Risks of genetically modified organisms For all the good GMOs might do, there are potential dangers in their use. Opponents of GMOs worry that continuous large plantings of crops with Bt genes will quickly select for resistant insect pests, making the genes useless. They are also concerned about the escape of genes from GMO plants to weedy relatives. For example, if herbicide-resistant genes escape to related weed species, they may become herbicide resistant. Opponents also are concerned about the difficulties in assessing the many unknown gene interactions when a foreign gene is introduced.
Some opponents have ethical concerns about the movement of genes outside natural processes.
There are potential dangers in the misuse of any genes. The continuous use of plants with Bt genes could result in the selection of resistant pests, but so can the repeated use of Bt sprays. Genes for disease resistance, pesticide resistance, or pesticide production that are selected through traditional breeding can cross into weedy relatives, just as they can from genetically engineered plants. The risk of gene escape to weedy relatives depends on the plant. Some have important weed relatives, and others do not.