Tag Archives: Tree Disease


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Using Dormant Horticultural Oil to Treat Tree Insect Infestations

The major difference between the newer horticultural oils and past dormant oils is that they are much more refined and they are useable throughout the year. Most horticultural oils are refined from petroleum oil. 

dormant horticultural oil being sprayed by an arborist for tree insects and diseaseThe refined oil is combined with an emulsifying agent; this allows the oil to mix with water which makes spraying easier. Originally dormant oils were heavier and less well-refined, however, they have been replaced with light weight, better refined oils that can be applied all year round on foliage without damaging it. The time of application is now why it is referred to as dormant oil and not the properties of the oil.

That said, there are other oils that can be used to deter insects and tree diseases and they are; Mineral oil, summer oil, Supreme oil, Superior oil, Vegetable oil, Cottonseed oil, Soybean oil, and Neem oil. Our www.72tree.com arborist can apply the horticultural oil to treat any insect infestations and diseases you may have. Listed below are the uses, precautions and benefits of the dormant tree oil.

The Use and Application of Horticultural Oil

Horticultural oils are effective, safe and they do not harm useful insects. Spraying should be done before buds swell and can be sprayed even if the buds are slightly swollen. This may damage some of the buds but the advantages overshadow the damage. Here are some benefits of the horticultural oil:

• They smother and kill insects.
• They disrupt the feeding of insects which is important in stopping the spread of plant viruses by aphids.
• They can also be used against powdery mildew.

When you buy concentrated Horticultural spray oil, you will need to dilute the product to create your spray. Some oils require mixing with water, so be cautious and follow the appropriate instructions. When the oil is liquified and sprayed on, the application may appear thin and disappear quickly as it dries. Don’t mistake this and ignore the prescribed application instructions. When applied consistently, you will notice scales falling off and insects avoiding your trees or plants.

Precautions – Oils shouldn’t be used on oil sensitive plants and when temperatures are high (100° F) or very low. Also, if rain is likely to fall or the plant is wet then application should be avoided. Do not apply oils in freezing weather as it can cause the emulsion to produce uneven coverage. Finally, when shoots are growing, oils shouldn’t be sprayed. 

Protection Year Round from Insects and Diseases

During the growing and dormant seasons, protecting your shrubs, ornamentals, vegetables, shades and fruit trees is important. Properly applied horticultural oil can help control and deter spiders, insects, moths, aphids and plant disease from killing your trees, shrubs, vegetables and plants.