For the gardener keen on avoiding commercial insecticides on fruit trees, the best natural alternative is to make horticultural oil that works by smothering insects when the trees are in their dormant period in the winter. These oils are safe to apply, effective and allow you to avoid the use of poisons that can accumulate in both fruits and the natural environment. Although its effectiveness isn't well-recognized by botanists, a natural alternative to insecticide sprays for use in the summer is available.
So-called "dormant" horticultural oils are applied before buds swell and break in the spring. They are used to kill scales, aphids and other mites and insects that spend the winter on the plant. They work by suffocating the egg cases of insects.
Horticultural oils integrate easily with plants and dissipate through evaporation. They are less toxic than pesticides. They pose little risk to people and to natural enemies of insect pests. They also can disrupt the feeding patterns of many insects, including aphids that transmit plant viruses. In some cases, oils interact with the fatty acids of insects and interfere with their metabolism.
Oils to use
Cottonseed oil is considered the best oil to use for dormant spray, although soybean oil can also be used.
Spray No. 1: Mix 1 cup of vegetable oil with 2 tbsp. of liquid soap. Add a gallon of water and stir. Shake it often while you're using it.
Spray No. 2: Mix a gallon of vegetable oil, a half gallon of water and 1 lb. of oil-based soap in granular form. Dilute one part of this with 20 parts of water. Because the ingredients separate quickly, you need to use this immediately after it has cooled.
Natural Bug and Fungal Spray
This spray is intended to keep insects and fungi away from your fruit trees during the summer.
If you have it, begin with 1 or 2 cups of compost tea. To make this tea, dilute a gallon of mature compost with 2 to 5 gallons of water; don't use compost that has manure in it. The compost tea is optional for this recipe.
Add 1 tbsp. of liquid seaweed, 1 tbsp. of apple cider vinegar, 1 tbsp. of Murphy or other wood-based soap, 1 tbsp. of molasses, and a gallon of water.
The liquid seaweed, the molasses and the compost tea fight fungi and feed the plants. You can buy the seaweed in a plant nursery.
The vinegar helps kill fungi and powdery mildew.
The soap helps the spray stick to the leaves.
Applying Fungal and Bug Spray
Spray very early in a morning with no wind. This allows the spray to dry before the leaves get hot and you won't get spray on your neighbor's plants. Apply a light mist on the tops and undersides of all the leaves.