Q. Do you prefer Neem oil or Horticultural oil when spraying fruit trees?
A. Horticultural oil is used for spraying trees and shrubs when leaves are absent during the winter. Horticultural oils, sometimes called dormant oil or even dormant spray, have a very specific viscosity or “thickness” which makes them effective in killing pests. These oils are petroleum-based and refined so they don’t damage plants if applied correctly.
When spraying trees, fruit trees and shrubs make sure the entire plant is covered with horticultural oil from “head to foot”. Neem oil is used primarily during the growing season when leaves and the offending insects are present.
Neem oil is a bit “trendy” right now. And it is plant-based rather than petroleum-based which for some is important. One major difference between neem oil and horticultural oil is the “toxicity” of neem oil toward some insects. Horticultural oil is not “toxic” on its own. It relies on “suffocating” insects for control.
Remember, just like many “organic” pest control chemicals, neem oil is nondiscriminatory in what it kills. It cannot recognize a good insect from a bad insect. You direct the spray towards pests you want to control or food that you want to protect. This is also true of horticultural oils but, unlike neem oil, is frequently applied when leaves and fruit are not present.
Neem oil has been promoted for disease control. A little known fact is that horticultural oils will control nearly all of the same diseases as neem oil. Similarly, horticultural oils can be applied when leaves and fruit are present as long as temperatures are below 80° F.
Personally, I have never found neem oil particularly effective in killing pests although I do use it in rotation with soaps and other organic pest controls. I worry a little bit that there is a wide variation in the “quality” of neem oils being produced and available on the market. Horticultural oils are pretty much all the same. Stay with name brands of neem oil.