DIY Organic Pest Control

Less expensive than their commercial counterparts and definitely more natural, these suggestions for DIY pest control techniques and sprays will keep your garden healthy and organic.

By Gwen Kilcherr


Fall 2012

Mineral oil

Since commercial pesticides may be harsh to the garden, family and pets — as well as be toxic to beneficial insects and wildlife — the idea of homemade pest-control sprays appeals to many.

Photo by Karen Keb

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Homemade remedies are inexpensive and have been used with satisfying results in controlling harmful insects and diseases. Using safe, non-toxic, natural, homemade insecticides to control garden pests gives many homeowners and organic gardeners peace of mind because they know what’s going into their garden. The fear that commercial pesticides may be harsh to the garden, family and pets, as well as being toxic to beneficial insects and wildlife, makes the idea of homemade pest-control sprays appealing to many.

Prevention

The easiest way to prevent insect damage in your garden is to discourage them from coming in the first place. A healthy garden is where it all starts.

Pull out any weak-looking plants as they may already be infected. If not, they will attract insects.

Build a healthy, organic soil. Natural composting methods, mulching and top-dressing your soil with compost and/or natural organic fertilizer is the best way to develop strong, vigorous growing plants. Seaweed mulch or spray contains trace elements such as iron, zinc, barium, calcium, sulfur, and magnesium, which promote healthy development in plants. Seaweed fertilizer in these forms will improve growth and give plants the strength to withstand disease. Seaweed mulch also repels slugs.

Minimize insect habitat. Keep the garden area clear of debris and weeds which are the perfect breeding areas for insects.

Interplant and rotate crops. Many insects are often plant specific. When plantings are mixed, pests are less likely to spread throughout a crop. Rotating crops each year is a common method to avoid re-infestation of pests which have over-wintered in a particular area.

Keep foliage dry. Water early in the morning so the foliage will be dry for most of the day. Wet foliage encourages insect and fungal problems on the plants.

Disinfect. If you've been working with infested plants, clean your tools before moving onto other plants in the garden. This will help reduce the spread of insects and diseases.

Before mixing up your own homemade pest-control concoctions, keep in mind:

Always test first. As always, with any new spray you want to try, test it on one or two leaves of your plant first to make sure it doesn't burn the foliage or have any adverse reactions before spraying the entire plant. You never know what kind of reaction plants will have, so it's better to be safe than sorry.

Spray early. Also, always spray first thing in the morning when the wind is calm and the temperature is cooler, to avoid running the risk of burning the plants; beneficials are relatively inactive at this time too. Just because some sprays are homemade doesn't mean they can't harm the beneficial insects; they can, so pay attention to what you’re spraying and if you see beneficials in the area, you may want to wait.

Note that because homemade mixtures have no preservatives, you're better off dumping any you have left over, and simply mixing a fresh batch every time you want to spray.

Non-Toxic and Homemade Remedies

Alcohol Sprays:

The idea of using rubbing alcohol as a spray for plant pests has been around for years.  Alcohol sprays work on aphids, mealybugs, scale insects, thrips and whiteflies.

How to make: Use only 70 percent isopropyl alcohol (rubbing alcohol): mix 1 to 2 cups alcohol per quart of water. Since alcohol can damage plants, remember to test your spray mix on a few leaves or plants first. If there’s going to be any damage, it should show up within 2 or 3 days.

Garlic Oil Spray:

Organic gardeners have long been familiar with the repellent or toxic affect of garlic oil on pests. Providing a quick kill, it will control a wide range of insects including aphids, cabbage loopers, earwigs, June bugs, leafhoppers, squash bugs, and whiteflies; plus a few fungal diseases like leaf spot and mildews because of garlic’s anti-fungal properties. The spray does not appear to harm adult lady beetles and other beneficials.

We've all heard about and used garlic sprays for organic pest control for years, but you usually just see recipes that only contain garlic and water. This recipe is very effective for many reasons, particularly because it contains three things that bugs, and some fungi, simply don't like: garlic, mineral oil, and soap.

How to Make: Soak 3 ounces of minced garlic in 2 tablespoons of mineral oil for 24 hours. Strain out the garlic and add 1 pint of water and 1 teaspoon of liquid dish soap to the remaining liquid. Mix together well

How to Use: Mix 1-2 tablespoons garlic-soap mixture with 1 pint water; spray plants as needed. 

Herbal Sprays:

Many organic gardeners are familiar with growing herbs to repel pests from the garden plants. Several recent studies confirm the repellent effect of such plantings. The essential oil of sage and thyme, and the alcohol extracts such as hyssop, rosemary, sage, and thyme can be used in this manner. They have been shown to reduce the number of eggs laid and the amount of feeding damage to cabbage by caterpillars of diamondback moths and large white butterflies. Sprays made from tansy have demonstrated a repellent effect on imported cabbageworm on cabbage, reducing the number of eggs laid on the plants. Teas made from nasturtiums and wormwood have been used as sprays to repel aphids. Sprays made from ground or blended catnip, chives, feverfew, marigolds, or rue have also been used by gardeners against pests that feed on leaves.

How to Make: Herbal sprays are made by mashing or blending 1-2 cups of fresh leaves with 2-4 cups of water and leaving them to soak overnight. Or you can make an herbal tea by pouring the same amount of boiling water over 2-4 cups fresh or 1-2 cups dry leaves and leaving them to steep until cool. Strain the water through a cheesecloth before spraying and dilute further with 2-4 cups water. Add a very small amount of non-detergent liquid soap (¼ teaspoon in 1-2 quarts of water) to help the spray stick to the leaves.

How to Use: Spray the plants thoroughly, especially the undersides of leaves, and repeat at weekly intervals if necessary.

“Hot” Powders (Dust)

Black pepper, chili pepper, dill, ginger, paprika, and red pepper all contain capsaicin, a compound shown to repel insects. Capsaicin-containing dusts repel onion maggots from seedlings, as well as other root maggot flies from cabbage family plants, beets, and carrots. Pepper powder around the base of the plants help repel ants, which is very desirable in a garden where ants often protect and maintain aphid colonies on plants.

How To Make: It can be rather expensive to buy enough packaged pepper powder to sprinkle throughout your garden. However, if you grow and dry your own red peppers, chili peppers, or dill, you can make lots of powder very inexpensively. Use a mortar and pestle to grind the peppers (or dill) including the seeds, to a powder. Be careful handling the hot peppers because they irritate sensitive skin and cause eye irritation.

How to Use: Sprinkle the powder along seeded rows of beets, cabbage, carrots, and onions, in a band at least 6" wider than the row or planting bed. A fine sprinkling will suffice, but the more dust you use, the better the results. If possible, try to keep the powder from getting wet. You will have to reapply 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.

Pepper Sauce Spray

Combine 1 teaspoon of hot pepper or Tabasco sauce with four cloves of garlic and a quart of water. Blend well in a blender and strain with a cheesecloth or nylon mesh before pouring into your sprayer. This will repel many insects including aphids, caterpillars,  spidermites, and whiteflies. Spray as often as needed.

Soapy Solutions

Make your own insecticidal soap that will help to control soft-bodied insects such as aphids, mealybugs, spidermites, thrips, whiteflies, and many other insects.

Use a soft liquid soap such as Ivory liquid dish soap, Murphy's Oil soap, or Castille soap. These are biodegradable and can kill insects in a similar fashion to commercially manufactured brands. (Do not use detergent soaps because these can be problematic to your plants' health.) Mix three capfuls, of any of these soft soaps, with 1 quart of water, for a very effective insecticidal soap. These soft soaps will only last about a day or two before they start to dissipate. They need to be reapplied if overhead watering is used or after a rain.


Gwen is a private landscape consultant and designer, specializing in residential garden design. She is co-host of Sonoma County’s “Garden Talk” show on KSRO 1350 AM radio with Steve Garner, Saturdays from 9 a.m. to 11 a.m. Gwen has written a Q&A garden column in her local newspaper, The Press Democrat, for more than 20 years.