Autumn is an excellent time to apply horticultural oil. The oil smothers many soft-bodied insects and hard-shelled scales that are impenetrable to many insecticides, and can therefore help control some of the most stubborn insect populations. But is it right for your plants?
About Horticultural Oil
Horticultural oil, or hort oil, is typically derived from petroleum, and is a type of ecologically-friendly mineral oil. Some cottonseed and soybean oils can also be effective horticultural oils. Emulsifying agents are typically added to these oils so they can be mixed with water and used as a spray, which helps distribute them evenly over plant foliage to be most effective.
Pests That Don’t Like Horticultural Oils
Different types of horticultural oils can be effective against many unwanted garden pests, including…
- Spider mites
- Aphids
- Whiteflies
- Mealy bugs
- Psyllids
- Lace bugs
- Caterpillars
In addition to smothering the larvae or insects directly, the heavy oil also makes it difficult for many insects to crawl therefore starving them to death and preventing them from spreading diseases from plant to plant. Additionally, the oil repels many insects looking for winter homes. The oils also act as fungicide against powdery mildew, rust and leaf spot on some plants.
Applying Horticultural Oils
Application of horticultural oils is easy, requiring only a simple hose-attached sprayer. Because oil and water do not mix, frequent agitation by shaking is required even if the oils are mixed with other agents to be more sprayable. These products are most effective if applied when plants are dormant, since oil-based products can burn and harm actively growing foliage, buds, flowers and fruit. Some lighter weight, summer-formulated oils are available, but they should be used only sparingly and only if absolutely necessary. Autumn and winter are the best seasons to apply horticultural oils when insects are a problem, though autumn applications can occasionally cause problems with plants dying back and other winter damage. Because the oils can evaporate and dissipate quickly, they should only be used when insects are present, otherwise they will be ineffective. In freezing weather the oil coverage will be inconsistent, so cool but not bitterly cold temperatures are best.
Of course, always follow the instructions for proper application rates, plant sensitivity and ideal weather conditions to ensure the most effective treatment. Because these oils are still pesticides, protective gear such as gloves and goggles should also be worn to avoid accidental irritation or more severe contamination.
Using hort oils can be a great way to control insects on your plants, but only if the oils are used appropriately. Come in for a consultation to see if these products can help end your insect problems.
