Homemade fruit tree sprays have the benefit of using lower concentrations of organic fungicidal and insecticidal compounds. They also take advantage of such household ingredients as dish soap, vegetable oil and baking soda. Resist the temptation to "make it a double" by using too high a ratio of any of these ingredients when diluting them in water. Too much of a good thing can burn fruit tree foliage or, as in the case of baking soda, cause a buildup of sodium in the soil.
Oil-Based Pest Spray
Professionals use horticultural oil to smother insect eggs and larvae, but home growers may get good results when using vegetable or mineral oil. The optional step of infusing the oil with botanicals such as hot peppers and garlic adds repelling power to the insecticidal properties of the oil spray. Use a heavy-weight spray -- similar to commercial "dormant oil" sprays -- in early spring to prevent yearly problems like scale insects. This heavier concentration is appropriate once the temperature is above 40 degrees Fahrenheit but should be applied before the trees have flowered.
To cope with problems such as spider mites, aphids and mealybugs that emerge in the summer, use less oil per water to mimic commercial "summer oil" sprays. In this case, the temperatures should still be below 90 F.
Peel cloves from a head of garlic, and roughly chop one or two hot peppers. Add them to 2 cups of vegetable or mineral oil.
Infuse the botanicals for about 24 hours, about then strain the oil.
Dilute the oil mixture in water, using a ratio of about 20 to 25 parts water to 1 part of the oil mixture -- more oil per water for late winter sprays and less oil per water for summertime sprays. Add the blend to your sprayer.
Coat the entire tree with your homemade oil spray.
The fatty acids in soap can kill plant-eating pests such as aphids, scale insects, mealybugs and whiteflies while making it harder for pests to land on, and lay eggs upon, the trees. Soap sprays have less sticking power than oil sprays, so you need to reapply them more often, especially after rainfalls. The good news is that household liquid soap is relatively inexpensive, and you don't need to use much of it in relation to the water in which it will be diluted.
Blend 2 teaspoons of nondetergent, mild soap into 1 gallon of water. Stir to blend well.
Pour the mixture into your spraying device.
Coat the top and bottom surfaces of the foliage, as well as other problem areas, of the fruit trees. If you have a problem such as scale insects on the woody parts of your fruit tree, spray trunks and branches as well. It is also safe to spray the fruit, even on the day of harvest.
Reapply once every week or so while the insect problem persists or after heavy rains.
Baking Soda Spray
Baking soda, or sodium bicarbonate, has fungicidal properties, making it potentially useful for preventing common fruit tree fungal diseases, such as powdery mildew and Botrytis. When blended at low concentrations, baking soda spray is mild enough to be applied about once a week or so during the growing season, if needed.
Measure 2 teaspoons baking soda and add it to 1 gallon of water. Add a drop or two of mild dish soap or other nondetergent liquid soap. The small amount of soap helps the watery mix adhere to plant surfaces. Stir the mixture until the baking soda dissolves.
Pour your baking soda blend into your spraying apparatus and apply to your fruit trees. Focus on the leaves of the fruit trees, making sure to coat both lower and upper surfaces of leaves.
Repeat as needed throughout the growing season but not more than once a week.