Plant Answers  >  Dormant Oil Spray

Return to Gardening Columns Main Index

Dormant Oil Spray
by Jerry Parsons, Ph.D.
Horticulture Specialist, Texas Agricultural Extension Service in San Antonio

How would you like to have your limbs cut off? How would you like to have your body beaten, bumped and bruised periodically? How would you like being stripped naked by ravaging hordes? How would you like to have your root cut, compacted and covered? And worse yet, how would you like to be an invalid totally dependent upon another uncaring, complacent individual for your hygienics? If you find all of the above situations distasteful you certainly don't want to be a tree.

Trees can tolerate and actually appreciate a limb removal periodically - it opens things up and lets the sun shine in. Trees are understanding of careless lawn mowers who bump their bark and bruise their bodies. Even though it damages them internally and scars their appearance, most trees are capable of compensating for the abuse. In Texas most trees expect to be periodically defoliated by hordes of pests, whether insects or disease, and keep reserve leaf buds and life elements in order to survive such trauma. People cannot see and consequently ignore one of the most vital parts of a tree - the roots. Consequently roots are indiscriminately cut by digging around trees, compacted by heavy traffic patterns and machinery and covered with suffocating soil by builders. All of these are bad but by far the worse and deadliest is human neglect of tree hygiene. A tree is basically an invalid - it cannot care for itself! When it is contaminated by Texas' pestilence it needs your help. Now is the time to act to rid your defenseless trees and shrubs of inconspicuous killers by using a prophylactic spray.

The spray which should be used is referred to and sold under many brand names as dormant oil or scale emulsion. These are highly refined oils (not motor oils!) which spread uniformly on the bark of trees and shrubs to which it is applied and coat non- mobile, dormant insects on the tree smothering them to death. Heavier oils may have to be applied with a tank (pump-up) sprayer which can apply the fully diluted product rather than with a hose-end sprayer which may become clogged. Applicators should frequently shake sprayers to agitate the water and chemicals mixed since plant damage can occur if a concentrated oil spray, caused by solution separation, is applied. Mix dormant oil at the recommended rate on the product label. This usually involves mixing one-fourth pint of oil per gallon of water.

Insects possibly controlled are phylloxera on pecan and grape (causes leaves to be curled and distorted), San Jose scale and cottony cushion scale on fruit trees, ornamental shrubs and trees (whitish, snow-like covering on branches) and some mites which might be asphyxiated too.

If you want to "sweeten the pot" and kill more for your effort, add a copper fungicide such as Kocide 101 (one tablespoon in one-half gallon). If a copper fungicide is added, the spectrum of control is increased to include peach leaf curl (puckered leaves in spring), brown rot (soft brown spots on ripening fruit), coryneum blight (tiny holes in leaves which are too numerous and concentric to have been caused by insects), anthracnose on blackberries (lesions on canes and discoloration of leaf areas) and some scab (black lesions on pecans and shriveled, drawn areas on pecan foliage).

If you really want to insure pest annihilation fortify the dormant oil mix with an insecticide. The addition of such an insecticide kills active scale as well as dormant scale which is suffocated by the oil coverage. Entomologists (bug killers) recommend the chemical Diazinion. The recommended amount to add is 1 1/3 tablespoons per gallon of water in which one-fourth pint of dormant oil and two teaspoons of Kocide 101 has been mixed. All of these elements are compatible and can be mixed together with no adverse effects.

It is best to spray before buds begin to swell. If buds of trees and shrubs have begun to swell slightly, go ahead and spray. Although some of the buds may be damaged, the benefits of spraying dormant oil plus a copper fungicide far outweigh the possible repercussions. Besides, fruit trees have many more fruit buds than they need to produce an adequate crop anyway - - you won't have to thin the fruit as much thus avoiding the moral issue of abortion! Do not spray trees which are in full bloom however. Applying a dormant oil spray after the pruning season will also serve to cover pruning cuts which have been recently inflicted and can serve as a second attack on stubborn pests which were not killed by an earlier oil application.

Spraying of dormant oil should occur on a clear day when the temperatures are expected to remain over 50 degrees F. for at least twenty-four hours. The ideal temperatures for application is between 40 and 70 degrees F. Try to avoid applying dormant oil when severe freezing trends are expected in the 3-4 days following application. Some plant damage might occur if freezing occurs before the spray water evaporates.

Now is the time for annihilation of much of the pestilence which can cause a lot of a trees' hygienic problems this spring. However, you must act with a blind faith (prophylactically) that you may have some of these pest problems on your trees and the treatment is effective since few of the intended victims are visible. Pest control at this time of the year is for prevention of potentially damaging situations. If these particular pests are not controlled now with this sight-unseen technique, they may become painfully apparent this spring when their control will be difficult if not impossible.

You must also become a sadistic killer of pestilence for the good of your plants. Pests will be suffocated by a thin film of oil! Better that they are "wasted" now than your plant this spring! A word of caution: The use of a dormant oil mixture will not only kill, but annihilate, annual flowers such as pansies, bluebonnets or snapdragons growing under or near plants to be treated. To insure domestic tranquility, completely cover such tender vegetation before spraying nearby trees and vines with dormant oil. The use of dormant oil spray is anorganic pest control technique which will control the overwintering stages of harmful organisms with sprays which are safe to handle and non- toxic to people. But better yet, application of this spray is cheap insurance to make sure that you as a caretaker of nature's invalid trees, shrubs, and vines are never reported to plant- abuse-central as a contributor to plant life demise.


Listen to the Garden Show live!
Saturday & Sunday from Noon-2PM
Call (210) 308-8867 or (866) 308-8867
and have your gardening questions answered
- during show hours ONLY -
Milberger's Gardening South Texas
Hosts: Dr. Calvin Finch, Dr. Jerry Parsons, and
Milton Glueck, radio personality and host
Last weekend's shows ON PODCAST
Podcast Logo
Milberger's Specials
On Sale This Week | Newsletter Signup
Local Gardening Events
Open 9 to 6 Monday-Saturday & 10 to 5 Sunday
3920 N. Loop 1604 E.  San Antonio, TX 78247
Phone: (210) 497-3760
Three exits east of 281, inside of 1604.
Next to the Valero station.
Email Us | Map & Directions
Copyright © 2022 - All Rights Reserved. PLANTanswers and are trademarks of Jerry Parsons.