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Away With Holey Leaves: Offing the Pests

I can't stand the tell-tale signs of garden pests: the leaves with holes, the failure to thrive. I believe in early assault with organic deterrents. Kate has great faith in plants' commitment to survive.  She considers holes in leaves to be a mere cosmetic blemish.

Like politics and religion, getting rid of pests in a garden is sure to cause a community donnybrook (or at least rapid words over ice water in the lounge chairs).

To do organic warfare against pests means using one or more of these tools:

  • Predatory insects. Certain wasps and praying mantises are examples of insects that eat the pests that eat the plants.
  • Companion plants. This was discussed in an earlier post. Pairing specific plants (marigolds and tomatoes, for example) repels insects that feast on one of the plants.
  • Botannical insectides. These are made from plant materials. One of the most widely used is an extract from the flowers of the pyrethrum daisy (Chrysanthemum cinerariifolium). While the powdered flowers themselves are rarely available, many products contain their active ingredients. Low concentrations are used because they are so effective. They are nontoxic to most mammals and degrade quickly in light or moisture. They can safely be used around food. Others include rotenone, ryania, sabadilla and neem. Botanical insecticides are not all equal,  so beware. Rotenone, for example, is as toxic as some synthetic insecticides.
  • Using microbes, most commonly Bacillus thuringiensis (Bt). Various strains of Bt are naturally present in soils around the world. When certain pests eat the right strain of Bt, the toxins the bacterium makes kill the pest by destroying the lining of its gut. Kurstaki Bt (Btk) kills catepillers that grow into gypsy moths, horn worms and cabbage worms. Tenebrionis Bt (Btt) kills leaf beetles such as the Colorado potato beetle. Bt strains are highly selective, thus sparing the beneficial insects in a garden. On the downside, they must cover the plant well to be effective; they break down quickly in sunshine and water so they don't last more than a few days; and they also kill butterfly larvae.
  • Horticultural oils, which smother insects by plugging the holes through which they breathe. Used improperly, they can also damage the plants that you're trying to protect. Solid coverage of the plant is essential. Horticultural oils can be effective against white flies, young scales, mites and other pests as well as some plant diseases. They aren't harmful to humans or wildlife.
  • Insecticidal soaps, which are effective against small, soft-bodied insects such as aphids, leaf hoppers and spider mites as well as some larger insects such as Japanese beetles. They work quickly, but it is essential to have the plant well covered by the soap. Rain, lawn sprinklers or minerals in hard water will all make insecticidal soaps less effective. They tend to spare beneficial insects and do no harm to humans or other wildlife.
My favorites are the insecticidal soaps. They are cheap and easy to make and safe to use. Here are some recipes for making your own:


The Simple Serial Killer
Mix 1.5 teaspoons of real soap (i.e., not detergent) in a quart of water. Spray it on plants to fight mites, white flies, aphids, thrips, small scales and leaf hoppers. Don't apply it on humid, windy or sizzling hot days. It can burn some plants with dull leaves, so test a leaf or two before dousing the entire plant.

Be sure to use true soap. The fatty acids from the animal fats used in the soap are what makes this work. The fatty acids dissolve the insects' exoskeleton causing them to dehydrate.

Drunken Simple Serial Killer
This is a variation of the above with the addition of alcohol. Alcohol affects many types of insects and is often included in many over-the-counter insecticidal soaps.  Mix a cup of rubbing alcohol with a teaspoon of Simple Serial Killer and a quart of water.  Spray on the top and bottom sides of plant leaves every three days for two weeks. This works well against scale on houseplants.

Drunken Dawn
This is a simplified version of the above. Combine 3 tablespoons of rubbing alcohol with 1 teaspoon of Dawn dish washing detergent and one quart of water. Spray the top and bottom sides of the plant leaves. Let the plant sit for three minutes.  Rinse the leaves thoroughly and then let the plant dry outside.


Soap and Salad Solution
Mix 1 cup of vegetable oil with 1 tablespoon of real soap to fight aphids.  Mix well so the two ingredients are thoroughly blended.  Then add 2 teaspoons of the mixture per cut of water in a spray bottle.  Shake the spray bottle well before using. Spray the plant wherever there are signs of bugs or all over as a preventative measure.  This mixture can affect some plants, so test it and observe the plant for a few days before gong wild.


North Hollywood Community Garden Pest Remover
The North Hollywood Community Garden recommends the following for eliminating pests: 1 tablespoon of baking soda, 1 tables spoon of light summer oil (SunSpray Ultra-Fine Spray Oil, for example) or vegetable oil, a squirt of dish washing detergent (optional) and a gallon of water. Mix together well.  Put in a sprayer bottle, shaking well before each use. spray plants about every four or five days to help control blackspot mildew, several types of rose pests and early blight on tomatoes.  The trick is to use it diligently.

Garlic Pesticide Spray
Hack up about 3 to 4 ounces of garlic bulbs (don't worry about the paper skins, you're going to strain it). Soak them in 2 tablespoons of mineral oil for a day. Dissolve 1 teaspoon of fish emulsion in a pint of water and add it to the garlic-oil solution.  Stir well.  strain the liquid and store in a glass container.  Use 1 part garlic-oil-fish emulsion solution to 20 parts water as a spray to kill aphids, mosquitoes and onion flies.

If you plan to make your own pesticides, a spray bottle is indispensable. One that allows you to adjust the spray to be narrow or broad is especially useful.

Because homemade insecticides often call for mixing substances that don't like to rub elbows, like oil and water or soap and oil, a mixer bottle or blender can be helpful in emulsifying the ingredients until you get them sprayed on the plant.

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