To ensure a large, healthy harvest from your fruit trees, you must give them a certain amount of care to control insect pests and diseases. Chemical products are commonly used and are available at nurseries, but for those who want to garden without toxic materials, organic sprays are the answer.
When a tree is in good health, it will be able to withstand and perhaps ward off attacks by insects and diseases. Before you plant your tree, amend the soil with organic compost and then apply a layer of mulch around young trees in spring. Good mulch materials include compost, seaweed, straw, wood chips or other organic materials. Make sure the mulch does not touch the tree's trunk. You can also scatter chicken manure and blood or bone meal on top of the mulch to nourish your tree throughout its growing season.
Liquid Manure Spray
Compost tea is a good remedy for fortifying the health of fruit trees that are beginning to show signs of disease or insect infestation. Place 1 qt of compost into a large container that can hold more than 10 gallons of water. You can also include chopped-up plants such as nettles, seaweed or comfrey in your tea mixture. Then fill it with water and let it steep for about one week, stirring it every day. Keep the container covered and then strain it. Mix 1 part of compost tea with 4 parts water and place the liquid in a sprayer. Spray the tree's foliage and the soil surrounding your tree until it is well saturated. Compost tea will also improve your tree's productivity, according to the Fantastic Farms website.
Insecticidal Soap Spray
Aphids and other soft-bodied sucking insects sometimes attack fruit trees. These insects are easily killed with a combination of a mild dishwashing soap and water. You can purchase ready-to-use insecticidal soap at nurseries and garden supply stores or you can make your own. Use Ivory soap or another non-ultra, mild dishwashing liquid and mix 1 or 2 tbsp. soap with 1 qt of water in a spray bottle if your tree is small. You'll need a larger amount and a larger spray mechanism for larger trees.
Horticultural Oil Spray
Sometimes called dormant spray, horticultural oils effectively smother insects that live on the fruit tree year-round. You spray a tree with dormant spray in winter or early spring before it begins to form leaves and blossoms. Dormant spray often includes lime sulfur, which helps to control fungal diseases when the spores are dormant. If your tree has never had a problem with fungal or bacterial diseases, you can omit the sulfur and spray with only horticultural oil and water.
To kill caterpillars and prevent fungal diseases, spray your fruit tree with organic sulfur mixed with water during its dormant period. Some fruit trees, especially apples, are subject to a disease called scab. Michigan State University's website advises spraying trees early in the season, at the time when buds begin to appear. Spray with sulfur every three to five days until the petals fall from blossoms. It's important to also spray before a rain, if you have advance warning. Mix .65 oz of liquid lime sulfur to each gallon of water or 3.4 oz of sprayable sulfur to each gallon of water.