Remember that, while organic sprays are often less invasive than commercially available chemical concoctions, all contain ingredients that could be harmful in strong enough concentrations or if misapplied. Always treat organic sprays with caution.
Alcohol Sprays
The idea of using rubbing alcohol as a spray for plants pests has been around for years. Can cause leaf damage on African Violets and Apple trees.
Protection offered: Alcohol sprays work on aphids, mealy bugs, scale insects, thrips and whiteflies.
How to Make: Use only 70% isopropyl alcohol (rubbing alcohol): mix 1 to 2 cups alcohol per quart of water. Do not use undiluted. You can also mix an insecticidal soap spray according to the dilution on the label but substitute alcohol for half of the water required.
Tomato Leaf
Nightshade family plants, such as tomatoes, potatoes and tobacco, have toxic compounds called alkaloids in their leaves. These toxins are water soluble and can be soaked from chopped leaves and made into home-made sprays. These sprays also work by attracting natural pest enemies. The good bugs follow the smell of the spray in looking for prey.
Protection Offered: Tomato leaf sprays protect against aphids. A scientific study has shown that corn plants sprayed with tomato leaf spray attracted significantly more trichogramma wasps to parasitize corn earworm eggs than the unsprayed did.
How to Make: Soak 1 to 2 cups of chopped or mashed tomato leaves in 2 cups of water overnight. Strain through cheesecloth or fine mesh, add about 2 more cups of water to the strained liquid, and spray. For aphid control, be sure to thoroughly cover the leaf undersides, especially of lower leaves and growing tips of plants where aphids congregate.
Garlic Oil Sprays
Organic gardeners have long been familiar with the repellent or toxic affect of garlic oil on pests. When combined with mineral oil and pure soap, it becomes an effective insecticide. Some studies also suggest that a garlic oil spray has fungicidal properties.
Protection Offered: Good results, with quick kill, have been noted against aphids, cabbage loopers, earwigs, June bugs, leafhoppers, squash bugs, and whiteflies. The spray does not appear to harm adult lady beetles.
Soak 3 ounces of finely minced garlic cloves in 2 teaspoons of mineral oil for at least 24 hours. Slowly add 1 pint of water that has 1/4 ounce liquid soap or commercial insecticide soap mixed into it. Stir thoroughly and strain into a glass jar for storage. Use at a rate of 1 to 2 Tablespoons of mixture to a pint of water.
To check for possible leaf damage to sensitive ornamentals, do a test spray on a few leaves first. If no leaf damage occurs in 2 - 3 days, spray more.
Herbal Sprays
Many organic farmers are familiar with using sprays made from aromatic herbs to repel pests from the garden plants. Several recent studies confirm the repellent effect of essential oils of sage and thyme and the alcohol extracts such as Hyssop, Rosemary, Sage, Thyme, and White Clover can be used in this manner. They reduce the number of eggs laid and the amount of feeding damage to cabbage by caterpillars of Diamond back moths and large white butterflies. Sprays made from Tansy have a repellent effect on imported cabbageworm on cabbage, reducing the number of eggs laid on the plants. Teas made from wormwood or nasturtium are reputed to repel aphids from fruit trees, and sprays made from ground or blended catnip, chives, feverfew, marigolds, or rue have also been used by gardeners against pests that feed on leaves.
Protection Offered: Try herbal sprays against any leaf-eating pests and make note of what works for future reference.
Herbal sprays are made by mashing or blending 1 to 2 cups of fresh leaves with 2 to 4 cups of water and soaking overnight, or you can make a tea by pouring the same amount of boiling water over 2 to 4 cups fresh or 1 to 2 cups dry leaves and leaving them to steep until cool. Strain before spraying and dilute further with 2 - 4 cups water. Add a very small amount of non-detergent liquid soap (1/4 teaspoon in 1 to 2 quarts of water) to help spray stick to leaves. You can also buy commercial essential herbal oils and dilute with water to make a spray.
"Hot" Dusts
Black pepper, chili pepper, dill, ginger, paprika, and red pepper all contain capsaicin, a compound shown to repel insects. Synthetic capsaicin is also available for use. Researchers have found that as little as 1/25 ounce of capsaicin sprinkled around an onion plant reduced the number of onion maggot eggs laid around the plant by 75%, compared to a control plant.
Protection Offered: Capsaicin-containing dusts repel onion maggots from seedlings, as well as other root maggot flies from cabbage family plants and carrots. Pepper dusts around the base of the plants help repel ants, which is desirable in a garden where ants often protect and maintain aphid colonies on plants.
Sprinkle along seeded rows of onions, cabbage, or carrots, in a band at least 6 inches wider than the row or planting bed. A fine sprinkling will suffice, but the more dust you use, the better the effect. Renew after a heavy rain or irrigation. To protect plants from ants, sprinkle around the base of plants in an area as wide as the widest leaves.
Pyrethrin
The dried, powdered flowers of the pyrethrum daisy, Tanacetum cinerarifolium, were used as early as 1880 to control mosquitoes. The popularity of pyrethrum insecticides waned when synthetic insecticides were introduced, but they are now enjoying a commercial comeback. Many new products formulated with natural pyrethrums are available. Pyrethrums, which are mainly concentrated in the seeds of the flower head, are a contact insecticide, meaning the insect only has to touch the substance to be affected. Pyrethrins have a quick knockdown effect on insects: Flying insects are paralyzed. Pyrethrins can be applied up to one day before harvest because they are quickly destroyed by light and heat and are not persistent in the environment. Pyrethrins will kill lady beetles but do not appear to be harmful to bees. They are toxic to fish and to the aquatic insects and other small animals that fish eat. Pyrethrins do not seem to be toxic to birds or mammals.
Pyrethrins are registered for flowers, fruits, and vegetables, including greenhouse crops. They are effective on many chewing and sucking insects, including most aphids, cabbage loopers, celery bugs, codling moth, Colorado potato beetles, leafhoppers, Mexican bean beetles, spider mites, stink bugs, several species of thrips, tomato pinworms, and whiteflies. They are especially good against flies, gnats, mosquitoes, and stored products pests.
If you grow your own pyrethrum daisies, you'll have the main ingredient for a make-it-yourself spray. The concentration of pyrethrums is at its peak when the flowers are in full bloom, from the time the first row of florets open on the central disk opens too the time all the florets are open. Hang flowers in a dark spot to dry. Once the flowers have dried thoroughly, grind them to a fine powder, using a mortar and pestle, old blender, or small hammer mill. Mix with water and add a few drops of liquid soap. Store in a glass jar and keep the lid tightly closed, because the mixture looses activity if left open. You'll have to experiment with the amount of water to add, because the concentration of pyrethrins in the flowers is an unknown variable. If the spray you make does not seem to kill insects, use less water the next time you make the concentrated spray. Also keep in mind whole flower heads stay potent longer so do not grind until ready to use.
Pyrethrins are more effective at lower temperatures, so for best results, apply in early evening when temperatures are lower. Spray both the upper and lower surfaces of the leaves, because spray must directly contact the insects such as thrips that hide in leaf sheaths and crevices. The first spray will excite them and bring them out of hiding, the second will kill them. Never use pyrethrin products around waterways and ponds.
Nicotine
One of the top three insecticides in the 1880s, nicotine in several forms is still widely used. Nicotine comes from the tobacco plant and is extremely toxic to insects. The great advantage of home-made nicotine tea is that it is very short lived, retaining its toxicity for only a few hours after spraying. It is relatively non-hazardous to bees and lady beetles because of its short persistence.
Protection Offered: Nicotine is effective against ground and soil pests, especially root aphids and fungus gnats, and on many leaf-chewing insects, such as aphids, immature scales, leafhoppers, thrips, leaf miners, pear psylla, and asparagus beetle larvae.
Brew your own batch of nicotine tea by soaking pipe tobacco leaves in water to make a spray. Soak 1 cup of dried, crushed leaves in one gallon of warm water with 1/4 teaspoon pure soap added. Strain and spray after 1/2 hour. The solution will keep for several weeks if stored in a tightly closed container.
For soil pests, pour the spray mixture onto the soil in the area of the stem base and root zone. Nicotine can be absorbed by plant leaves and remain there for several weeks; so, use nicotine only on young plants and only up to one month before harvest. Do not use on eggplant, peppers, or tomatoes. While most tobacco cultivars now grown are resistant to tobacco mosaic virus, nicotine sprays could contain the pathogen, which will infect nightshade family crops.
Tobacco teas are sometimes prepared by home gardeners to control garden pests, and while not as toxic as nicotine sulfate sprays, any nicotine solution toxic enough to kill insects can also be harmful to humans.
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