- What Is Dormant Oil: Information About Dormant Oil Sprays On Fruit Trees
- Spraying of Dormant Oils
- How and When to Use Dormant Oil on Fruit Trees
- When should dormant oil sprays be applied to apple trees?
- Dos & Donts of Dormant Oils
- How Dormant Oil Works as an Insect Control
- Pests Controlled With Dormant Oil
- Homemade Dormant Oil Recipes
- Dormant Oil for Fruit Trees
- Applying Homemade Dormant Oil
- Applying Dormant Oils Can Help Protect Your Trees
- Get a leg up on fruit tree problems with dormant oils
- What is Dormant Oil Spray?
- Dormant Oil Is An Eco-Friendly Oil
- When to Spray Dormant Oil
- How to Protect Your Lawn
- Lawn Coach Tip
- Horticultural Oil
- How to Effectively Use Dormant Oil
- Ask Ruth: Organic Horticultural Oil for Fruit Trees
What Is Dormant Oil: Information About Dormant Oil Sprays On Fruit Trees
In late winter, your fruit trees may be dormant but your chores in the yard aren’t. Late winter and early spring, when the temperatures are barely above freezing, is the time to apply the best preventative for scale and mites: dormant oil.
Dormant oil sprays are used on fruit trees before the buds begin to swell and suffocate insects and their eggs nesting in branches. Using dormant oil on fruit trees doesn’t completely eliminate the problem with these pests, but it is the best way to cut off most of the population, leaving a simpler problem later in the season.
Spraying of Dormant Oils
What is dormant oil? It’s an oil based product, typically petroleum but can also be vegetable oil based, especially designed for use on fruit trees. This oil has had surfactants mixed in to enable it to be mixed with water.
Once the oil solution is sprayed on all the branches of a fruit tree or bush, it penetrates into the surface of the insect’s hard outer shell, and suffocates it by not allowing any oxygen to get through.
Apples, crabapples, plums, quince and pears all benefit from dormant oil, as do gooseberry and currant bushes. Other fruit-bearing trees and bushes don’t have any need for spraying of dormant oils, as they don’t often harbor the same pests, but it won’t hurt to do so if desired.
How and When to Use Dormant Oil on Fruit Trees
To determine when to use dormant oil, look to your own weather. The date changes every year, but the conditions must be the same. Spray early enough so that the buds on the trees haven’t yet begun to swell. Wait until the daily temperature is at least 40 degrees F. (4 C.), and will stay that way for at least 24 hours. Finally, choose a 24-hour period when no rain or high winds are predicted.
Cover any annual flowers you may have near the tree when using dormant oil. While the weather is generally too cold yet for annual transplanting, if you are hardening off marigolds, snapdragons and other flowers, remove them from the area, as dormant oil will kill them off with no chance of revival.
Fill your sprayer with the oil solution and slowly cover the tree, beginning with the topmost branches. Move all around the tree to get the spray into all the crevices.
When should dormant oil sprays be applied to apple trees?
Dormant oil sprays are highly refined petroleum products that are mixed with water and applied to trees and shrubs to control aphids, spider mites, and scale. Dormant oils destroy pests by suffocating them. When applied properly, the thin film of oil plugs the spiracles or pores through which the mite or insect breathes.
Proper timing is critical when using dormant oil sprays. Dormant oils should be applied in late March or early April before the plants show signs of breaking dormancy (before “bud break”). Dormant oils applied in February or early March are not effective as insects are not actively respiring at this time and, therefore, are not vulnerable to the oil’s suffocating effects. Dormant oil sprays should be applied as close to bud break as possible.
Dormant oil sprays on fruit trees provide little benefit to most backyard gardeners. Dormant oil sprays do not control the major home orchard pest, the apple maggot, and the pests that are controlled by dormant oil sprays are seldom significant.
Dos & Donts of Dormant Oils
Dormant oils were originally developed centuries ago to combat stubborn scale and mite infestations on fruit trees. At first, these oils were heavy and poorly refined, making them unsafe to use on woody plants after they have broken winter dormancy. Nowadays, horticultural oils are lightweight and highly refined (and can even be used at diluted rates during the summer), so the term “dormant oil” now refers to the time of application, rather than a particular type of oil.
Dormant oils are especially useful for treating overwintering eggs of insects that curl leaves in the spring (such as aphids), the overwintering of eggs of tent caterpillars and leaf rollers, mites that overwinter on conifers, and scale nymphs and adults. These oils kill pests by either blocking the spiracles through which they breathe or interfering with their metabolism. Using horticultural oils in favour of insecticides is now widely recommended, since oils pose little risk to humans, other mammals, birds or beneficial insects; don’t cause pests to build up a chemical resistance; evaporate quickly; and can be applied using existing spray equipment (always follow package directions to the letter).
The majority of dormant oils available are refined petroleum products (mineral oils) that are filtered, distilled and de-waxed before they’re combined with an emulsifying agent, which allows the oil to be mixed with water before spraying. Dormant oils can be applied from late winter until two weeks before buds open. Be sure the temperature will remain above freezing for at least 24 hours and there isn’t any precipitation in the forecast. Spray on a dry, sunny morning to facilitate fast drying.
Many of the new, lighter horticultural oils are also suitable for summer use to combat adelgids, aphids, leafhoppers, mites, scale insects, whitefly and powdery mildew.
– Stephen Wstcott-Gratton
Did you know?
Not all trees and shrubs tolerate dormant oil; those that are sensitive include:
Japanese maple (Acer palmatum and cvs.)
Red maple (A.rubrum and cvs.)
Sugar maple (A.sacchorum and cvs.)
Hickory (Carya spp. and cvs.)
Eastern redbud (Cercis condenses and cvs.)
Smokebush (Cotinus spp. and cvs.)
Japanese cedar (Cryptomeria japonica and cvs.)
Beech (Fogus spp. and cvs.)
Japanese holly (Illex crenata and cvs.)
Walnut (Juglans spp. and cvs.)
Blue Junipers (Juniperus, blue cultivars)
Norway spruce (Picea abies and cvs.)
Dwarf Alberta spruce (P. glouca ‘Conica’)
Colorado spruce (P. pungens and cvs.)
Eastern white pine (pinus strobes and cvs.)
Douglasfir (Pseudotsuga menziesii and cvs.)
Red oak (Quercus rubra and cvs.)
Yew (Toxus spp. and cvs.)
Cedar (Thuja spp. and cvs.)
Sometimes I think that pests, like scales, aphids and mites adore my fruit trees as much as I do. They feast on the juicy tender plant parts in the warm summer and overwinter on my fruit trees. Dormant oil does help control these annoying little pests and homemade dormant oils are safe for use on fruit trees. Homemade dormant oils are easy to make at home and provide the same benefit as store bought dormant oils without the petroleum (because you choose the oil) and it is soooo much cheaper to make your own.
As recently as 10 years ago, dormant oils contained heavy petroleum based oils that had to be applied during fruit trees’ dormancy in order to prevent damage to their foliage and buds. Today, newer dormant oils are lighter, allowing them to be applied at anytime during the year without harming the tree’s buds. Because you can apply homemade dormant oil throughout the season, the term “dormant” is a bit of a misnomer now, but is still a benefit as you will see.
How Dormant Oil Works as an Insect Control
Dormant (or Horticultural Oil is usually combined with some type of emulsifying agent so that it can be mixed with water and used as a spray. The primary way horticultural oil kills insects is by suffocating them. The oil blocks the spiracles through which insects breathe.
Horticultural oils also disrupt the metabolism of insect eggs and the ability of some insects to feed, causing them to starve to death. Not a pretty picture, but remember that insects, like aphids, carry diseases from plant to plant by feeding.
Most commercial dormant oils contain kerosene or petroleum based oil that, when applied to trees, will smother overwintering insects like aphids, scales, mites, and their eggs or will dissolve their protective waxing coating. It is applied in the winter months when fruit trees are in their inactive period. (dormant) For dormant oil to provide proper control, the oil must come in contact with the pests. Dormant oils were further refined to produce lighter weight oils that can be applied during the growing season, without harm to many plants. When the term dormant oil is used now, it generally refers to the application timing, during the dormant season, rather than a type of oil.
Pests Controlled With Dormant Oil
- Adelgids: These small, sap-sucking insects are important pests in forests, landscapes, and Christmas tree plantations. Some are very difficult to control because of a waxy protective covering that they hide under.
- Aphids: sometimes called greenfly, are small insects that suck plant juices from stems and leaves and can severely stunt or even kill their host plants.
- Spider Mites: They are perhaps the most important agricultural and garden pests worldwide. Some researchers estimate that spider mites reduce total agricultural production by up to 5% each year.
- Thrips are tiny insects, most feed on leaves but some species are predators. Thrips feeding causes very distinctive silvery patches on the injured leaf. Thrips can be important pests in greenhouses because of the feeding injury as well as for a serious plant disease they can spread. Thrips, both plant-feeding and predatory species, also occasionally bite people. The bites are harmless but annoying.
- caterpillar eggs, leafhoppers, mealybug, scale, and whiteflies
are the most common pests that call for the use of dormant oil.
I did NOT know this and I haven’t tried it, but dormant oil is also effective against powdery mildew. The popular homemade baking soda recipe (recipe one below) includes horticultural oil as an active ingredient.
Also, since horticultural oil is effective against aphids, which spread viruses by feeding on plants, it is also somewhat of a virus control.
Homemade Dormant Oil Recipes
This recipe is to control soft bodied insects like aphids, mites and mealybugs, all you need is an organic oil, laundry detergent and water. Mix together 1 tablespoon of any lightweight organic oil (again, I used sunflower), a few drops of laundry detergent and a quart of water. Shake well and pour into a spray bottle to use. This mixture controls insects by smothering them, so make sure to use an adequate amount when applying it to your fruit trees. (Oh, bonus!) I use this solution as a preventative also, It works by smothering insect egg casings.
I have tried several homemade “dormant oil recipes” and they do help control pests on fruit trees. The first recipe I used, and the most basic, was created by the scientists at Cornell University to controls over-wintering pests and fungal diseases.
- 2 tablespoons of ultra-fine canola oil (I don’t use canola oil for anything, I used sunflower oil here)
- 1 tablespoon of baking soda
- a gallon of water
Mix the oil and baking soda in the water and viola, homemade dormant oil!
The scientists at Cornell University also came up with a nourishing dormant oil you can make at home.
- 2 tablespoons of any lightweight organic oil (again, sunflower oil)
- 1 tablespoon of baking soda
- 1 tablespoon of kelp
- 1 tablespoon of mild dish soap
- 1 gallon of water
Mix the first four ingredients together in the water and spray.
Sometimes insect control on your fruit trees requires a different approach. Another method for controlling insects on fruit trees is to apply a spray that deteriorates the waxy outer coating of the insect, thereby exposing it to the elements, which causes its downfall. To make a dormant oil spray for fruit trees that accomplishes insect control via this method, Mix all the ingredients together. Pour the mixture into a sprayer and shake it vigorously before applying it. The baking soda and hydrogen peroxide are an important part of this homemade dormant oil because they work to sterilize fungal spores that are potentially damaging to fruit trees. This spray is also great for use after pruning as a way to seal the tree and keep unwanted pests out.
- 2 tablespoons of baking soda
- 5 tablespoons of hydrogen peroxide
- 2 tablespoons of castile soap (which is made from an olive oil base)
- 1 gallon of water
Dormant Oil for Fruit Trees
There is an oil defense especially for use with fruit trees.
- 1 cup of vegetable oil
- 2 tablespoons of liquid soap (preferably castile)
- 1 gallon of water
The process is the same as in the above recipes… mix the oil and soap together in the water. Shake it good and keep shaking as you spray. This recipe is my “go to” I use for use when the tree is truly dormant. It suffocates insect eggs on my fruit trees. And as I mentioned above, many commercial dormant oil sprays contain petroleum based oils. This homemade mix provides a much less toxic substitution.
Applying Homemade Dormant Oil
All these dormant oil recipes are applied the same way. During the fruit tree’s dormancy (depending on your growing zone it will be any time the leaves fall or first frost and early spring before your fruit tree’s buds first open) Fill a pump sprayer with your homemade dormant oil and completely coat the fruit trees (stems and both sides of the leaves) with the mixture. Only apply the oil mixture when the fruit tree is dry. Moisture OR high levels of humidity will considerably lower the effectiveness of your dormant oil application. Note:
- Dormant oils generally won’t harm beneficial insects since they are applied at a time when beneficial insects aren’t present on fruit trees and have a low toxicity level to humans and mammals.
- Homemade dormant oils won’t leave a harsh residue behind.
- It loses its ability to check pests once it is dry, and can harm plants susceptible to oil sprays.
- Generally, the cedars, maples, spruce and junipers are susceptible tree species that dormant oil should not be used on.
When Not to Use Horticultural or Dormant Oil
- You should only apply dormant oil on dormant deciduous trees or shrubs when the temperature is between 40-70°F in late fall and winter. Do not apply oils during freezing weather as this can cause the emulsion to break down and produce uneven coverage.
- Do not apply oils if plant tissues are wet or rain is likely. These conditions inhibit oil evaporation. Dormant oil should not be used on evergreens.
- Do not apply when fruit trees are stressed out. (e.g. from sun scald or bark splitting caused by late spring frosts – after growth has started – cool summer followed by a warm fall and drop in temperature, excessive or late season nitrogen fertilization, dry soil or root injury, frost cracking, excessive temperature fluctuations and drying winds, lack of snow cover all which stress a tree out) Stressed out trees are more likely to become more damaged by dormant oil than it is worth.
- During extremely high temperature: Do not apply horticultural or dormant oil when temperatures are climbing high (esp. over 100° F. (38° C.) Drought-stressed plants are more susceptible to dormant oil damage.
- Living With Bugs Jack DeAngelis, PhD OSU Ext. Entomologi
- Cornell Horticulture
- Department of Plant Pathology and Ecology The Connecticut Agricultural Experiment Station
- Flanigan, Amada. Homemade Dormant Oil Spray for Fruit Trees
- Colorado State University Extension: Insect Control: Horticultural Oils
- Oklahoma State Extension Service – Dormant Oil
Applying Dormant Oils Can Help Protect Your Trees
While dormant trees may not be so easy on the eyes for us, overwintering insects still find their look appealing. Late in the summer, scale insects, mites and aphids will lay eggs on trees that stay on through the winter months until new larvae are born. These larvae can damage fruit trees, such as apple and pear trees, as well as certain shrubs and woody ornamentals.
Thankfully, you can help protect your trees and shrubs with dormant oils (also known as horticultural oils), a readily available and relatively inexpensive solution. An application of dormant oil will help control overwintering insect populations by coating the insects’ spiracles, effectively smothering future larvae. Best of all, the oils are less toxic to beneficial insects, such as ladybugs, as well as birds and mammals.
Applying dormant oil will help to keep your trees and shrubs healthy and give you a head start on insect management in the spring.
Here are four tips to maximize the effectiveness of an application of dormant oil:
Timing is everything. Dormant oils should not be applied until a tree has gone completely dormant, but also before new growth occurs. Applications in late winter or early spring are ideal, when temperatures are above freezing (over 40 degrees is ideal), but also below 70 degrees. Applying the oil too early may expose your tree to winter damage. Applying too late will damage new growth.
Coordinate with other applications. If you also apply a sulfur-containing pesticide, be sure to space out your applications. A combination of dormant oil and a sulfur-containing pesticide can create a compound poisonous to plants. To play it safe, wait 30 days after a sulfur pesticide application before using dormant oil.
Check the label. When choosing a dormant oil, look for a low-viscosity oil, which will spread more easily. Make sure the product you choose is specifically marked as a dormant oil, as other oil types can damage trees and shrubs. Also, be aware of the types of trees and shrubs your dormant oil is formulated to protect. A dormant oil for your apple tree might be harmful for a woody ornamental elsewhere on your property.
Apply with caution. Follow all instructions on the label when applying a dormant oil and be aware of your tree or shrub’s surroundings. If you aren’t sure how or when to apply, contact a local, licensed professional. Nearby annual flowers, in particular, can be damaged.
Get a leg up on fruit tree problems with dormant oils
CORVALLIS, Ore. – Just when you’re ready for a long winter’s nap, it’s time to tend your fruit trees.
If you don’t, chances are they’ll struggle in the coming season. Giving them attention now helps ward off insects and diseases, said Steve Renquist, a horticulturist for Oregon State University Extension Service who has taught hundreds of gardeners the basics of managing fruit trees.
Applying dormant sprays – Superior oil, copper, and sulfur – helps control nasty pests and diseases like codling moths and apple scab.
Superior oil, also called horticultural oil, is a highly refined miscible oil (up to 99.9 percent pure) that when mixed with water and sprayed on trees will smother overwintering insects and their eggs. It targets mites, aphids, leaf hoppers, mealy bugs, leaf miners and more.
Lime sulfur is a fungicide that controls fungal diseases like apple and pear scab and peach leaf curl.
Copper is a fungicide and bactericide that controls diseases like bacterial blight, fire blight and Nectria canker. It kills bacteria and fungal spores left in the trees, including Pseudomonas syringae, a common bacteria that can cause gummosis, which is oozing of bacterial infested honey-like sap from bark split. In a rotation of copper and sulfur, the copper will deal with bacteria and sulfur will target fungal diseases best.
With a spray regimen of all three – used in conjunction with good hygiene and pruning practices – most fruit tree problems can be nipped in the bud, according to Renquist.
The trio of pesticides, which can be used in organic gardens, fit snuggly into the realm of IPM or integrated pest management, a practice that uses a variety of low-risk tools to deal with pest problems and minimize risks to humans, animals and the environment.
“They are a really important part of good IPM,” Renquist said. “When you’re planning a program, you want to use products that have low toxicity, and won’t cause a lot of problems for the environment. Dormant sprays score pretty well. Their toxicity level for animals is pretty low if you follow the labels. Superior or horticultural oil kills target insects, but beneficial insects are rarely around trees in the dormant season.”
A good reference for disease and pest control is Extension’s Managing Diseases and Insects in Home Orchards, which has a list of cultural practices and least toxic products for various pests and diseases. For information on specific products contact your local master gardeners.
Renquist recommends a three-pronged approach to spraying. In fall around Thanksgiving, apply copper. Spray sulfur in early January and then at least two weeks later make a spray with dormant oil. Then make another copper spray in mid-to late February. Don’t combine copper and sulfur or sulfur and oil in the same tank to minimize the risk of damage to tree bark.
If you don’t like to spray or forget the early spray, Renquist said the January application is the most important. This year, if you’ve missed the January timing, you’re still better off to make the third spray.
Some tips from Renquist:
- Apply Superior or horticultural during the dormant season to allow for greater coverage and a higher likelihood of getting to a majority of insects.
- Spray when temperatures are above freezing but before buds break.
- Don’t mix copper and sulfur in the same tank.
- Prune trees to keep the branches separated for good pesticide coverage and good hygiene. The best time is in January so that the last spray or two will cover the pruning wounds.
- Clean up fruit, leaves and debris under trees. They can harbor insects and diseases. If you don’t want to rake leaves, mow over them a couple of times and leave them to decompose.
- Clear weeds from around the trunk and under the tree where insects and rodents can hide.
- Add organic matter around trees for fertility and because enhanced microbial populations in the soil will help devour the remnants of orchard sprays that fall to the ground.
- Accept a little damage to fruit.
- When planting fruit trees, consider dwarfs so you don’t need a ladder for spraying.
- Read the labels of all products you use and follow the instructions. Using any pesticide incorrectly is not only harmful to you and the environment, it can actually cause damage to the very plants you’re trying to benefit.
For more information on fruit trees, refer to Extension’s Growing Tree Fruits and Nuts in the Home Garden and Training and Pruning Your Home Orchard.
What is Dormant Oil Spray?
This year, get a jump start on yearly insects such as scale, borers, and mites with a dormant oil treatment.
If you’ve had problems with insect attacks on your trees or bushes this past year, here is a good way to start off the season.
Dormant Oil Is An Eco-Friendly Oil
The dormant oil spray is a highly refined mineral oil. This treatment is non-toxic to humans and pets which will mean there is no wait time for getting back out on your lawn. This spray treatment for trees and shrubs works by drowning out or suffocating any over-wintering larva that are anxiously awaiting to feed on your new tree and shrub leaves.
When to Spray Dormant Oil
To begin spraying, the weather must be above freezing. Dormant oil should be applied in late February or throughout the month of March. This treatment can be sprayed on to all trees and bushes that are not considered blue, such as Spruce or Juniper trees. The only exception to this rule is Pine trees.
How to Protect Your Lawn
With a combination of dormant oil, quarterly bug barrier treatments, and a 100% satisfaction guaranteed Eco Pride Program your home can be successfully protected from pesky pests. The bug barrier will keep add a protective force field around your home to prevents bugs from ever finding their way in.
The Eco Pride Program covers all the treatments in and around your home and guarantees your satisfaction or your money back. Then as stated before the dormant oil prevents pests from ever hatching to become a problem.
Lawn Coach Tip
“When you are clearing leaves from your lawn, make sure you clear out beneath your bushes as well. This will help avoid bugs from over-wintering in that area which will help reduce the population for next Spring.” – Jeremy Swope
For more information about dormant oil or other tree and shrub programs call a lawn coach today!
More Articles Written by Wes Ory
SOPHIE THOMSON: Ants crawling on these branches have alerted me to the fact that this Kaffir Lime has scale. Now that’s these tiny brown inanimate looking lumps – they actually look harmless enough – but they secrete a sweet honeydew and that attracts the ants. It can also lead to a secondary problem called sooty mould. Now the solution is simple. All we need to do is spray with a horticultural oil and I can show you an easy way you can make your own with ingredients you’re likely to have in the kitchen.
Now the best thing about this is not only is it easy, but it’s safe and everything I’m using is non-toxic. And it’s so simple. We start with 2 cups of vegetable oil and then a half a cup of dishwashing detergent. Simply mix it up together. When you shake it, it goes a really milky colour and that’s where it gets a name ‘White Oil’ and it will actually store safely for a couple of months.
To use it, all we do is we add 2 tablespoons of the concentrate to a litre of water and it’s ready to go. How simple was that?
Horticultural Oil works by suffocating the insect pests, so it’s really important that you get good coverage, making sure you get the oil covering all over the insects. It is also effective in the control of aphids, white fly, leaf miner, mealy bug and mites on roses, other citrus, stone fruit and most house plants. Be careful not to spray in hot weather as it can burn and avoid spraying soft-leafed plants like lettuce and fern. You should also avoid using oil sprays within a month of the applying a sulphur-based fungicide.
Horticultural Oil is a safe and effective insecticide and it will certainly kill off this scale, however if we see ants crawling on the stem again, I’ll be back.
STEPHEN RYAN: The Gardening Australia ‘Gardener of the Year’ competition throws up some brilliant entries, but unfortunately, there can only be one winner and you’ll find out who that is on next week’s show. But throughout the year we’re going to bring you some of the runners up – starting with one that Jane visited recently.
How to Effectively Use Dormant Oil
What is dormant oil?
Dormant oil refers more to when the oil has traditionally been applied rather than what it is made of. Newer dormant oil formulations are typically refined from petroleum oil, such as mineral oil. Unlike home remedies, they also contain an emulsifier to help water mix with the oil, which will provide more complete coverage of plant surfaces. Dormant oil may also be labeled as horticultural, superior or all-seasons oil; keep reading for more on this.
How does dormant oil work?
Dormant oils were first utilized to control insect pests on fruit trees, where an effective control that wasn’t harmful to pollinators and was safe for ingestion by humans was needed. The oil covers leaf and limb surfaces, suffocating insects and some insect eggs, which reduces harmful insect populations. It may also interfere with insect feeding. Dormant oils don’t leave a toxic residue and dissipate quickly, making them ideal for use on blooming plants that will have pollinators arrive later during the growing season. It is also considered safe to use around humans and pets.
What pests does dormant oil control?
Dormant oil sprays can control a variety of insect pests such as aphids, mealybug, thrips, whiteflies, adelgids, caterpillar eggs, leafhoppers, scale and mites. This control is more effective on young insects and less effective on more mature insects so timing and early intervention is key. With the destructive, newly discovered Crape Myrtle Bark Scale wreaking havoc in Little Rock, applying Dormant Oil is a crucial step in saving crape myrtles. Read our blog post for additional control methods for CMBS. Dormant oil can also help control powdery mildew, a common foliar disease. Because dormant oil can be an effective aphid control, and aphids vector and spread viruses, it could be said that it also helps reduce plant viruses.
When should dormant oil be applied?
Although more traditional dormant oils should only be applied when a plant is dormant, newer formulations can be sprayed at alternate times of the year at a lower application rate. Because some new formulations may be used when the plants are not dormant, be aware that they may be called superior oils, horticultural oils or all-season oils. Since recommended application rates and temperature ranges differ between dormant oils, it’s imperative to read each product’s label and follow directions carefully. Failing to do so could result in plant leaves burning or essentially suffocating a plant. A good rule of thumb is to avoid spraying on sunny days (even during cooler weather) and avoid spraying when temperatures are freezing or close to freezing. The emulsifiers aren’t effective in low temperatures and coverage will be uneven. Also, avoid applying when severe freezing trends are expected within the following 3 to 4 days. Apply in early morning or late afternoon, and avoid spraying on days that temperatures above 90 degrees are expected. The ideal temperature range for application is between 40 and 70 degrees, with the day of application expected to stay above 50 for at least 24 hours. Drought stressed plants are more susceptible to oil damage; do not spray on drought stressed plants. Conversely, applying during very humid conditions reduces the rate of evaporation and can also cause burning. Apply when rain is not predicted for the next 24 hours. Do not apply if a sulfur based pest control product has been applied within the previous 30 days as the oil and sulfur combination can be toxic to plants. Fruit trees should only be treated with dormant oil when dormant; which is prior to bud swell. Applications may be repeated on fruit trees in 3 to 4 week intervals.
How should dormant oil be applied?
Spray with hose end sprayer (better for larger plants as the spray will go further) or pump sprayer, making sure to cover entire surface of branches, trunk and underside of leaves. Thoroughly rinse container and spray ends of both type of sprayer with water after use. This is needed to remove any clogs that could form if the oil solidifies after use. There are plants that are sensitive to oil applications; a list can usually be found on the product label. Applying to houseplants may cause injury; treat small portions of plants to test before treating entire plants. Read directions carefully; including safety instructions.
Ask Ruth: Organic Horticultural Oil for Fruit Trees
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I missed the first spraying (dormant oil) for my fruit trees. When should I spray them and what do I use? Do I trust any spray labeled “organic”? I have dwarf apple, peach, pear, plum, and nectarine trees and I live in Pitt County in Eastern NC. Thanks in advance for any advice on this matter.
~Gayle Morgan, Pitt County
Talking about fruit trees is like opening a can of worms – it is a huge and complicated subject. Generally fruit trees are considered a higher maintenance adventure than other gardening endeavors, but the rewards are oh-so-sweet. Each fruit has its own special needs, and organic approaches to orcharding evolve every year.
Horticultural oils are used to smother insects and their eggs and to suppress overwintering diseases. Opinions vary about exactly when to spray dormant oil, and suggestions ranged from midwinter to late winter/early spring before the buds have begun to swell. Other recommendations were much more specific such as: when green tip is ¼ to ½ inch long (the buds are open at the tip and green is beginning to show).
In the mountains of North Carolina this usually occurs in February/March and probably earlier in Pitt County, NC. Lighter- weight horticultural oils (like all-seasons oil) may be sprayed anytime of year, using caution since sometimes the oil will damage plant leaves.
For horticultural oil to be effective, the oil must contact and coat the pest; complete coverage of the tree is very important, including the crevices/cracks in the tree’s bark and buds. Scale, mites, pear psylia, and aphids are some of the insects targeted by horticultural oil.
Oils should not be sprayed on plants when freezing weather is expected. Refrain from spraying during windy weather since much of your spray will be blown off course by the wind and will not end up on the tree. Likewise avoid rainy weather. If you spray just before a heavy rain, you will have to re-spray following the rain.
The spray you use should be mixed fresh each time you spray, so mix up only the amount you will use right then. Agitate the oil in your sprayer frequently so that it remains in suspension. You want a very fine mist of oil, not blobs. You will need one to two gallons of spray per 8-10’ tree when you are spraying dormant trees. If your trees are super-small, you could get by with a hand-held plant mister (your hand will cramp up pretty quickly if you have very much to spray). A two gallon pump sprayer works well in most garden situations. Be sure not to overfill past the fill line on the tank – or the gasket may blow.
I personally love using a backpack sprayer (3-, 4-, or 5-gallon), but they are a bit costly with about a $100 price tag. Having a sprayer with a wand is extremely useful for reaching into all the nooks and crannies and under leaves.
In lieu of dormant oil, organic orchardist Michael Phillips mixes up a concoction of diluted 100% neem oil with a tad of soap emulsifier, liquid fish, effective microbes, blackstrap molasses, and liquid kelp. On a warmish day, he thoroughly coats the tree and sprays the soil area in the tree’s dripline too.
Here is a list of a few OMRI Approved Oils. (Some may state restrictions for Certified Organic growers):
- Monterey Horticultural Oil (previously called SAF-T-SIDE): 80% mineral oil (92% unsulfonated residue of mineral oil) for control of fungal diseases, insects and mites. For year round usage-dormant and growing season. Use on most crops, including fruit and nut trees, vegetables, berries, ornamentals, grasses. Controls powdery mildew, mites, scale, botrytis, leafminers and more.
- Golden Pest Spray Oil – OMRI: 93% soybean oil. For Fruits, nuts, evergreens and woody shrubs. Controls mites, sooty mold, scale, whitefly, and mealybug.
- Bayer Advanced Natria™ Multi-Insect Control Concentrate – OMRI: 96% Canola Oil
- Concentrate Worry Free® Brand Vegol™ Year-Round Pesticidal – Oil – OMRI: 96% Canola Oil. For dormant and growing season use to control all stages of insects and eggs for roses, flowers, fruits, vegetables, houseplants, and trees.
- Ahimsa Organics Neem Oil *- OMRI: 100% Neem Oil. Note: This is pure, unformulated oil and is not registered for use as an insecticide, fungicide or for any specific herbal use. Use as an insecticide would need to be cleared with your certifier.
- Organic JMS Stylet Oil – OMRI: 97.1% paraffinic oil (superior grade white mineral oil). Used to control fungal diseases, insects and mites.
Note: ALWAYS check any product you intend to spray for suitability to your objective (does it target the pest you want to target?). Also check for safety precautions, mixing precautions, and general precautions – and follow the safety measures indicated on the product. Pesticide rules and organic rules change over time. Determine the current status of a product prior to use. Certified growers can check with their certifying agency.
- Organic Growers School Spring Conference Library. For two different apple/fruit organic spray programs, check out Organic Growers School’s own online library – featuring topics presented at previous OGS Spring Conferences. Under Pest Management see Organic Pest Management of Apples by Elizabeth Brown, and under Commercial Farmers see Organic Apple Spray Program by Ron & Suzanne Joyner.
- Cornell fact sheet on oils – Click on this link and scroll down to see OMRI listed Petroleum, Plant, and Fish Based Oils.
- Cornell Home Fruit Information.
- The Holistic Orchard: Tree Fruits and Berries the Biological Way by Michael Phillips, available from Chelsea Green.
Local Apples: Photo by Ruth Gonzalez
Other considerations for orchard health:
- Because of their smaller stature, dwarf (8-10 ft.) and semi-dwarf (12-15 ft.) fruit trees are easier to spray, prune, and harvest.
- Choose your location carefully – most fruit trees require full sun for good fruit production. Plant fruit trees halfway down the slope where they will enjoy good air drainage. Don’t plant at the bottom of a slope, or in frost pockets, where frost is liable to collect. In mountain locations where spring weather is sporadic, a northeast-facing slope makes an ideal orchard site – because northeast slopes stay cool longer in the spring and therefore the risk of frost damage is reduced.
- Prepare your planting hole well. Dig a generous wide hole, and plant your tree no deeper than it was in the pot. Backfill the hole with 50% native soil mixed with 50% compost. Soft rock phosphate, greensand, kelp and/or azomite can be added to the backfill as well.
- Water your fruit tree religiously for the whole first year and (after the first year) during dry periods. Water deeply to the bottom of the rootball. Most trees enjoy moist well-drained soil.
- Plant disease-resistant cultivars. Plant fire-blight resistant apples and pears.
- Check your pH. Ideal pH for many fruit trees is 6.5. Soil that is too acidic contributes to fire blight susceptibility.
- Don’t over-fertilize. Too much nitrogen produces succulent growth that is more susceptible to insects and diseases – such as fire blight.
- Employ good sanitation throughout the year. Pick up and dispose of fallen fruit. Rake up fallen and diseased leaves. Destroy diseased fruit, diseased branches, and diseased leaves (do NOT compost).
- Prune fruit trees regularly to maintain good air movement, and fruit access to sunlight.
- When fruit trees are in bloom, don’t spray insecticides since pollinators (such as honeybees) could be killed by the insecticide. I think it is always safer to spray oils very early or late in the day, so that the risk – of bee traffic and plant injury from sunburn – is minimized.
Gayle, not all organic products will be labeled OMRI, and restrictions apply to some OMRI-labeled products, but seeing OMRI on the label does help you quickly discern whether the product is considered organic. There is also an EPA label with three little leaves that reads “For Organic Gardening”. . Some companies, such as Seven Springs, label various products as NOP (National Organic Program) compliant.
Look for organic products in your local garden center/agricultural supply. If you cannot find the product locally, try Seven Springs Farm, Johnny’s Selected Seed, Peaceful Valley Farm Supply, or Harmony Farm Supply.
PS: Put the 2013 Annual OGS Spring Conference (March 9 & 10) on your calendar – this is our 20th year and cause for celebration!
Gardeners: Got a question for Ruth? Email it to us at [email protected]
Ruth Gonzalez is a former market farmer, gardener, local food advocate, and founder of the Tailgate Market Fan Club where she blogs at tailgatemarketfanclub.wordpress.com. In her job at Reems Creek Nursery, Ruth offers advice on all sorts of gardening questions, and benefits daily from the wisdom of local gardeners.
Ask Ruth © 2012 Ruth Gonzalez & Organic Growers School
Author: Ruth Gonzalez
Ruth Gonzalez is a former market farmer, gardener, and local food advocate who wants to see organic farms proliferate and organic gardens in every yard. She serves on the Organic Growers School Board of Directors, and in her job at Reems Creek Nursery, Ruth offers advice on all sorts of gardening questions, and benefits daily from the wisdom of local gardeners.