Plants have issues that some essential oils may resolve.
Try this . . .
essential oils for plant disease
This site is interesting . . .
http://www.gardenguides.com/77485-use-essential-oils-gardening.html
There may be a better solution for both plant disease and pest . . .
soil minerals that plants need to resist insects
This is relative
Brix and Insect Resistance
http://davesgarden.com/guides/articles/view/2401/The rest of the plant health issue is the rest of the nutrient system. Water - make sure the water is not laced with high additive toxins like chlorine and fluoride, lead and other ground water and delivery systems' sources, and the soil is toxic elements' free.
Using essential oils to correct these issues may have some effect, but the underlying cause needs attention.
Essential oils with antimicrobial properties can harm soil microbes that feed plants. in time light applications of these to the foliage will likely not harm soil microbes as the air and light and water break the oil down, and for soil properly protected by top mulch, there should be very minor harm at the most.
Some soil bacteria are stimulated by essential oils
https://www.researchgate.net/publication/226375162_Simulation_of_soil_microbial_activity_by_essential_oils
Chemoecology 9:41–45 (1999)
0937–7409/99/010041–05 $1.50+0.20
© Birkha¨user Verlag, Basel, 1999
Stimulation of soil microbial activity by essential oils
D. Vokou and S. Liotiri
Department of Ecology, School of Biology, Aristotle University, GR-54 006 Thessaloniki, Greece, e-mail: vokou@bio.auth.g
Simulation of soil microbial activity by essential oils (PDF Download Available). Available from: https://www.researchgate.net/publication/226375162_Simulation_of_soil_microbial_activity_by_essential_oils
Essential Oils as Green Pesticides: Potential and Constraints
http://projects.nri.org/adappt/docs/63-84.pdf
Selected Antimicrobial Essential Oils Eradicate Pseudomonas spp. and Staphylococcus aureusBiofilms
Your Organic Garden:
Pest Control Without Chemicals
http://www.sustainablebabysteps.com/organic-gardening-pest-control.html
Excerpt from above page . . .
"Neem Oil: This is an oil from the pressed seed of a Neem tree. It is used worldwide to repel insects, such as ants, aphids, beetles, caterpillars, cockroaches, houseflies, leafminers, mealy bugs, nematodes, snails, termites, and many more, including controlling fungus and mildew. It requires processing and should be purchased commercially for the proper concentrated use in organic garden pest control.
Garlic Oil Spray: Garlic oil is also used to repel insects. You can make a garlic oil spray by soaking fresh minced garlic in vegetable oil for several weeks. This can be mixed in a spray bottle with about 4 parts water to one part oil and sprayed on your leaves or around the stems of your plants. Alternatively, as described above with companion planting, some insects may also be repelled by planting an abundance of garlic closely together with other plants."
General uses chart
http://hopewelloils.com/usage.php
