Available in stores. Tabasco sauce is such an extract, as is Dr. Bronners Peppermint soap. These are also called Essential Oils. While they are used for human use they can also be used to control, kill, repel insects and to control many diseases. They control the frequency levels of plants such as they control human frequency levels.
Aromatherapy is useful for insect and disease control.
Used best at drops per quart or tablespoons per gallon. See specific oil. I am planning on doing research into this area. It kills staphylococcus, the typhoid bacillus, the diphtheria bacillus, the tuberculosis bacillus, as well as pneumococcus, hemolytic streptococcus and many other dangerous pathogenic microorganisms, and has strong anti-venom properties as well. Works well against most plant diseases if caught in early stages.