What’s Wrong with My Herbs: Natural Pesticides for Gardens
Q. Garden pests are eating my plants, but I don’t want to use harsh chemical pesticides. Are there natural pesticides for gardens I can make at home?
A. Yes, you can stop insect invaders without turning to dangerous pesticides. We rely on several common-sense strategies and time-tested herbal pesticides that almost always do the trick.
Homemade Insect Spray Recipes
Garden Pest Control: Keep Your Eyes Open
The strategies for staying ahead of garden pests are fairly simple. First and foremost, be aware of the life in your garden. Look for insects and mites and observe their activity daily, or as often as possible. Scout for common pests, such as aphids, cabbage worms and Japanese beetles, but keep in mind that some insects, such as ladybugs, lacewings and praying mantises, are beneficial predators that can help control pests. (For more about beneficial bugs, read Attract Beneficial Bugs to Your Garden.) If you have trouble identifying what you’re seeing, contact your County Extension agent, who can help.
Damaged leaves are a good indication that a plant is infested with some insect pest. If you look a bit closer, you’ll probably see eggs, larvae and/or adult insects. Check the bottom of leaves, where pests (especially spider mites) often congregate. Also examine stem junctions, where mealybugs hide their egg masses. Aphids are especially fond of the tender tips of plants, and ants even will carry them there to keep the population growing!
Spraying Pesticides Simplified
Now that you’ve determined that a pest has taken up residence among your plants, you can take actions to stop it. Begin with the least toxic, least expensive and most convenient method first: a strong spray of water.
You’ll need an adjustable nozzle turned to the fan setting. This will allow you to direct a wedge of water over a large plant surface. Adjust the pressure so the water will wash away pests without damaging the plant. Spray the entire plant, side to side and top to bottom–as well as the top and bottom of leaves–until the plant is completely clean.
The best time to spray water (or any control product) is in the cool of the day when plants are not in direct sunlight. In direct sun, water droplets act as tiny magnifiers, concentrating light on plant tissues and causing them to burn.
Plant-feeding pests also are less energetic and easier to target in the early morning and evening.
Natural Pesticides for Gardens: Organic Pesticide Recipes
Besides using these water baths to stop pests, we also use a homemade garlic-chile-soap spray, neem oil and horticultural oil, alternating among them monthly, if necessary, to keep pests off-balance.
For instance, after we spot an infestation, we first blast the plant with plain water, then follow with garlic-chile-soap spray every three to five days until the pest is gone. A single spray rarely removes all of the tiny pest eggs, which are attached to leaves with strong webbing. Also, rain washes off the soap spray, so you may need to respray every few days.
If the pest still is present after a month or so, we switch to a neem oil solution, applied according to package directions. And if neither the garlic-chile-soap nor the neem oil sprays do the trick after two months, we use horticultural oil spray the third month.
We find the following treatments very effective against most garden and greenhouse pests.
Soap-based sprays. Soap sprays adhere to leaf surfaces and damage pest’s cell membranes. Several commercial brands are available. Or, make your own soap spray using biodegradable soap as the base: 1 1/2 teaspoons castile, Basic H or Murphy Oil Soap added to 1 quart water, along with about 8 drops insecticidal essential oils. (Try our Herb and Soap Ant-Repellent Spray recipe.) We also include soap in our Garlic and Chile Insecticidal Soap Spray.
Neem oil. Derived from the neem tree (Azadirachta indica), neem oil kills, repels and interferes with pests’ ability to reproduce. It won’t harm mammals and is easy on beneficial insects.
Horticultural oils. These oils work by smothering pests. Use the refined “summer” types (also known as superior or verdant oils) to control soft-bodied insects during the growing season, when the temperature is below 90 degrees. Use heavier dormant oil on deciduous plants in winter.
Tip: Whenever you try a new spray, be sure to test it on a small area and wait a day or two before you spray the entire plant.
Learn More About Pests and Pest Management
Tina Marie Wilcox and Susan Belsinger are longtime Herb Companion contributors.
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