Negative and positive ions have been shown in studies to kill germs, while the specific mechanism is unknown, and some experts believe the germ-killing may be due to other factors. In any event, no proof exists that salt lamps have this effect. They may give off a glow when electricity passes through them, but this is not harmful. The virus theory for salting crops was popularized in the 1920s when it was believed that certain diseases were caused by viruses. Scientists today know this is not true, but it still is common for farmers to salt their fields to prevent disease. Salting works by desiccating soil (dry out the roots), which makes it harder for the plants to infect themselves with pathogens (disease-causing organisms such as bacteria or viruses). This does not mean salting will work on every plant problem, but it is effective against many problems including cedar apple bug damage to corn and soybeans. Salt should not be used as a cure-all for health issues, however; if your soil is lacking in nutrients, then salting it will do little to help your plants grow. It is also important to note that salting will not protect plants from pests such as insects or herbivores (animals that eat plants). Pesticides are the best way to control these problems. Finally, salting will not promote growth.