Dormant Oils and Horticultural Oils


Pictured Above: Lacebug damage on Azaleas in Fountain Inn, South Carolina


Editors Notes: when applying pesticides of any kind always read the label. This article’s goal is to simplify and direct and is not intended to be complete for all products and applications. If you need assistance, please contact a professional from your area or a local extension agent.


What are Dormant and Horticultural Oils

Dormant and Horticultural Oils are a less toxic forms of insecticide that can be used in the landscape on trees and shrubs. Dormant and Horticultural Oils have similar modes of action that are used to basically smother existing insects, their larvae, and/or their eggs. Dormant oils are often applied during the winter months of January and February to reduce the spring population of overwintering insects. Horticultural oils are often applied in the summer to control active pest populations. Dormant oils tend to be thicker and evaporate slower while Horticultural oils are thinner and dissipate quicker. Dormant and Horticultural oils are highly effective against pests such as aphids, whiteflies, scale, and mites which are often associated with carrying other diseases from plant to plant.


Advantages of Oils

Dormant and Horticultural Oils are a safer alternative to other more common insecticides and leave little to no toxic residues for wildlife and pets. With careful application (according to the label) it has little to no effect on the plant and local bee populations


Disadvantages of Oils

Timing is critical, so read the label carefully. If the temperatures are too hot then you can cause yellowing (phytotoxicity) to the plant leaves and too low can be an ineffective treatment. Most labels read that the temperature range is between 40 degrees F and 90 degrees F. Dormant oils can cause damage if applied to early in the winter, while too late can cause a delay to the new buds. There are some plants that are sensitive to treatments and this will also be indicated on the label, these often include cedars, spruces, and various maple trees.


In conclusion, I highly recommend Dormant and Horticultural Oils to be used in your landscape to replace more toxic landscape chemicals. If you have concerns applying it yourself, I recommend supporting a local Horticultural professional. If you're located in South Carolina, near Fountain Inn, Simpsonville, or the greater Greenville area feel free to give us a call and mention this post for a free quote or e-mail us with questions and ideas for another post: JHolmes@daffodilshorticulturalsolutions.com!


Need more info, Keep Reading some other helpful Articles:

-NC State (https://content.ces.ncsu.edu/horticultural-oils-for-ornamental-plants)

-Tuolumne County Master Gardeners: https://ucanr.edu/sites/Tuolumne_County_Master_Gardeners/files/161926.pdf 

-Washington State University Extension (https://s3.wp.wsu.edu/uploads/sites/403/2015/03/horticultural-oils.pdf)

-University of Nevada Extension (https://extension.unr.edu/publication.aspx?PubID=3029#:~:text=Dormant%20Oil%20%E2%80%93Oil%20applied%20to,insects%2C%20mites%20and%20some%20diseases.&text=Sometimes%20called%20superior%20oils.) 


Clemson University: https://hgic.clemson.edu/factsheet/armored-scale-insects-control/

University of California: http://ipm.ucanr.edu/PMG/PESTNOTES/pn7404.html 

Science Daily: https://www.sciencedaily.com/releases/2020/07/200728201558.htm 

Penn State: https://extension.psu.edu/phytotoxicity