Fruit trees are susceptible to several different types of insects. Aphids, coddling moths, red mites and fruit flies are all examples of insects that attack fruit trees. It is best not to use a chemical insecticide to kill these insects, since the chemicals can seep into the fruit. When the fruit is ingested, so are the chemicals. Fortunately, you can make your own insecticide at home out of horticultural oil.
Wait for a day when the temperatures outside are between 40 and 90 degrees Fahrenheit. You also need a day, preferably morning, that has little to no wind or rain. Once these conditions are met, you can make and apply your homemade oil spray.
Pour the horticultural oil in a backpack sprayer. This will make enough oil spray to cover one fruit tree.
Add water to the backpack sprayer. If you need to spray more than one fruit tree, you can double the horticultural oil and water measurements.
Shake the backpack sprayer to combine the two ingredients and then spray your fruit tree with it. Make sure you are getting under all of the leaves on the fruit trees, as this is where many of the insects like to hide.
Repeat once per month until you no longer have insects on your fruit trees.