Regional Gardening Reports :: National Gardening Association

In the Garden:
Southern California Coastal & Inland Valleys
July, 2001
Regional Report

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My tomatoes produce great quantities of fruits. I keep spider mites off my plants with regular sprays of water.

Controlling Pests

As long as there have been insects, diseases, and animals attacking gardens, destroying the vegetables and flowers you've so labored and loved, there have been organic approaches to hasten their demise. Some of these remedies sound good in theory only, while some have proven themselves effective for years. You'll never know for sure how they work until you experiment in your own garden with a few control techniques.

Keep Bugs at Bay

Insect pests can be grouped into two major categories, chewers and biters such as caterpillars, grasshoppers, and cutworms and suckers such as aphids, thrips, whiteflies, and scale. To discourage these pests takes different organic approaches.

I found I treat the chewers and biters with filtered sprays of pungent concoctions made from ground-up parts of aromatic plants such as marigold, garlic, onion, or hot pepper. I treat the second group with insecticidal soap or oil solution spray which smoothers the pests, coating and clogging their respiration systems.

Pungent Sprays and Traps

One stand-by pungent spray recipe I uses is 1 tablespoon liquid dishwashing detergent, 1 tablespoon tabasco sauce, 1 quart rubbing alcohol, and 1 gallon water. Be careful to wear non-absorbent rubber gloves and don't breathe the fumes. The tabasco liquid and vapor are very irritating.

You can also make simple traps to capture insects. Aluminum garden siding or boards laid on the soil will attract a variety of pests to the cool darkness underneath. Lift the boards in the early evening and destroy the pests.

Aphids and Nitrogen

An excess of insects in your garden may indicate nutritional imbalances in the affected plants. Aphids thrive on plants grown with excessive nitrogen. Ladybugs or insecticidal soap spray kill these sucking insects. To reduce the amount of nitrogen in the soil, add carbon-rich organic matter such as straw or sawdust. The nitrogen will be used by microorganisms breaking it down.

Whiteflies and Phosphorous

Whiteflies are attracted to plants lacking phosphorous (purple-green foliage) or magnesium (yellow between the leaf veins). You can release predatory wasps (they don't attack people or pets) to parasitize the whiteflies or hang a stickly yellow cardboard trap above plants to capture and kill them. Some sources of phosphorous you can add to the soil are wood ashes, bone meal, blood meal, fish emulsion, or poultry manure tea. Add dolomitic limestone to increase the magnesium.

Calcium and Spider Mites

Spider mites enjoy hot, dry weather conditions and plants deficient in calcium. Spray plants with a mixture of 1/2 cup of buttermilk and 4 cups of wheat flour to control the mites. Water deeply and more frequently to eliminate the moisture-stress condition which initiated the calcium deprivation.

Diatomaceous earth is fossilized remains on ancient sea creatures. When magnified, their skeleton looks like a cluster of pins pointing out of a ball. These "pins" prick the bodies of soft-bodied pests such as slugs causing their body fluids to drain out. While fatal to most insects, it has no harmful effect on people or warm-blooded animals.

Stop Nematodes

Nematodes are susceptible to drying out, so turning the soil after a crop is finished and allowing it to dry thoroughly can help reduce nematode populations. Infested plants and their roots should be destroyed, not composted.

Nematode damage develops on stressed plants when their root systems are unable to take up adequate water and nutrients. Nematode populations build up in the soil when the same crops are grown season after season. Rotating crops is a way to avoid this buildup. You can change your planting scheme as well. Vegetables that are relatively resistant to nematode include asparagus, cole crops such as broccoli, and sweet corn. Try growing these crops in areas known to have nematodes present.

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