Show While it is a bit early yet for home orchardists to begin a spray program, Extension offices have begun to get phone and email inquiries on timing for dormant oil sprays on fruit trees in home orchards and calls on managing Cedar Apple Rust and Apple Scab fungal diseases. Dormant oil sprays are typically applied to the point of run off to the branches and trunks of fruit trees to control over wintering adult insects and insect eggs that were laid last summer and fall as a means of lowering the insect pressure early in the season. Dormant oil sprays do not manage insects that are overwintering off your fruit trees or in the soil around your trees. These insects will be managed through your early multipurpose sprays and cover sprays as the growing season progresses during the summer months. Dormant oil sprays work by smothering the adult insect and soaking in to the overwintering eggs, effectively controlling them as well. This is why the instructions say to thoroughly cover the tree. Dormant oil sprays are temperature sensitive and will need to be applied when the temperatures are above freezing for 24 hours. This is the standard used, yet be sure to read the label of the product you are going to use for more specific guidelines. The dormant oils are mixed with water and if temperatures fall below freezing the oil and water separate, the effectiveness is greatly reduced. The sprays used to control Cedar Apple Rust and Apple Scab diseases are most often applied at what is called "bud break" This is when the bud scales start to swell and soften to allow either the flowers or foliage to begin to emerge. The bud scales soften during our spring rains, the same time that the fungal spores begin to emerge from their overwintering stages and float through the air infecting the very young flower and leaf tissues. Those first few sprays are critical to prevent early infestations that remain through the entire season and this is what most home orchardists find most challenging. Sprays need to be applied during inclement weather when we would rather be indoors. Another challenge to be recognized is that if it rains within hours of the application, you must go back out and reapply or the treatment is lost and the fungal spores arriving on your leaf tissues can infect anyway. Apple scab is the disease that will cause your leaves to fall off the tree and that impacts the fruit quality since the leaves are the source of the energy that grows the apple. Apple scab can also infect the fruit so the damage to your fruit trees is two-fold. Cedar Apple Rust is damaging as well as it impacts the leaves ability to produce food, it is just that those leaves remain on the fruit tree. The important thing to remember is those sprays have to match the trees development and the weather. You can use the calendar to measure the days between sprays, yet you cannot assume that the intervals between sprays remain constant. There will be more sprays more frequently in the beginning of the season and fewer sprays towards the end of the season. Your product label will also be helpful in this regard. Lastly, there will be "days before harvest" notation on the label, letting you know when you must stop spraying prior to harvest. About the author: Richard Hentschel’s expertise extends across several subject areas with specialties in lawn care, fruit tree production, woody ornamentals, and home and community gardening. During his 45-year career in horticulture and agriculture, Hentschel became a well-known and respected expert for commercial and homeowner audiences, industry organizations, and media. He retired from University of Illinois Extension in April 2022 with nearly 30 years of service as a Horticulture Specialist and Educator in northern Illinois.
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. 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. 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 snugly 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. 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:
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. |
How to spray dormant oil on fruit trees
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