It would be nice if no pesticides were necessary for the garden, but problems do occur. Left unattended, insects can ravage leaves, flowers and fruits and quickly spread disease. When a problem is severe enough to need control, always reach for the least toxic option first. That can be removing pests by hand or using an organic pesticide like the ones profiled here.
Remember, just because a pesticide is organic doesn't mean it does no harm. Always follow the label directions and keep in mind that more is not better, even with organic products.
Keep a close eye on your garden and try to catch problems early. If you practice good integrated pest management, with a wide range of plants, good growing conditions, natural predators, like birds and beneficial insects and healthy soil, you should not need to reach for a spray very often
Ingredients: Insecticidal soap is sodium or potassium salts combined with fatty acids
Application: Insecticidal soap must come in direct contact with the insect. It is no longer effective once it has dried
How It Works: The fatty acids in the soap penetrate the insect’s outer covering and cause the cells to collapse
- One of the safest pesticides
- Non-toxic to animals
- No residue
- You can use on vegetables up to harvest
- Can burn or stress plants. Don’t use in full sun or high temperatures.
- Does not work well for adult beetle pests which have developed a hard shell.
Precautions: Check label for specific plants that may be sensitive to insecticidal soap
Ingredients: Silica from the skeletons of tiny aquatic animals.
Application: Powder that is dusted on plants. May also be available in wettable powder or spray form.
How It Works: Absorbs fats and oils from the insect's exoskeleton causing it to dry up and die. Sharp edges help to pierce the insect allowing the powder to work quickly.
Pros: Non-toxic. Remains active for a long period as long as it is kept dry.
Bt (Bacillus thuringiensis)
Ingredients: bacteria. There are more than 80 types of Bt used as pesticides
Application: Generally available in powdered form that is sprinkled or dusted on a plant. It must be eaten by the targeted insect
How It Works: Bt is a stomach poison. It releases toxins in the stomachs of susceptible insects which cause them to stop eating and starve
Pros: Bt strains are very host-specific (hornworms, corn earworms, cabbage loopers and other caterpillar pests) and will not harm people, pets, birds or bees
Cons: Slow acting. It may take days for the insect to completely stop eating and die. Breaks down quickly, especially sunlight. Can kill ‘good insects’ like butterfly larva. Can be a skin irritant.
Precautions: Follow the label directions and don't overuse it
Ingredients: Contains 2 ingredients, azadirachtin (AZA0 and liminoids, both from the seed kernels of the neem tree fruit
Application: Sprayed onto plant leaves
How It Works: Upsets the insects' hormonal system and prevents it from developing to its mature stage. Most effective on immature insects and species that undergo complete metamorphosis
Pros: Non-toxic to humans
Cons: Washes away in rain. Slow acting. Breaks down in sunlight Indiscriminate pesticide
Precautions: Keep pets from treated leaves until they dry
Ingredients: Highly refined petroleum oil
Application: Mixed with water and sprayed onto foliage
How It Works: Coats and suffocates insects or disrupts their feeding
Pros: Low toxicity to humans, pets or birds. No toxic residue
Cons: Most effective against soft-bodied insects. Can cause bluish evergreens to temporarily lose their blue tint. Can burn leaves
Precautions: There are several grades. Be sure to use the one that is right for the season in which you are spraying
Ingredients: Derived from Chrysanthemum cinerariifolium
Application: Generally found in powder form and dusted on leaves.
How It Works: Poisons the insect, causing a quick death
- Pros: Quick acting. Low toxicity to animals. Degrades within a day.
- Cons: Broad spectrum insecticide. Kills any insect. Very toxic to honeybees
Precautions: Use cautiously, only when you have a major problem with hard-to-kill insects
Ingredients: Ground seeds of the sabadilla lily
Application: Comes as a fine powder and used as a spray
How It Works: Acts as a stomach poison
Pros: Very effective against the true bugs (members of the Hemiptera order)
Cons: Highly toxic to bees. Very irritating to the mucous membranes of mammals
Precautions: Use as a last resort
Ingredients: Derived from the roots of tropical legumes
Application: Dust onto plant
How It Works: Inhibits a cellular process, depriving insects of oxygen in their tissue cells
Pros: Low residual effect. Breaks down quickly in sunlight
Cons: Broad spectrum pesticide. Mildly toxic to humans when ingested.
Precautions: Apply in the evening, when bees are less active. May specific a "wait" interval before harvesting.
Ingredients: Potassium bicarbonate usually combined with horticultural oil and/or a substance to improve spreading and coverage of the leaves. There are commercially available products such as GreenCure® and Kaligreen, or you can prepare your own. Note: Baking soda or sodium bicarbonate is often recommended for similar fungus problems, however, research has shown potassium bicarbonate works better and is safer on plants
Application: Spray at the first sign of disease or use as a preventative before infection
How It Works: It’s still unclear, but it appears that bicarbonates can damage the cell wall and possibly create a pH that is not conducive to further fungal growth. The effect is immediate
- Lasts 2 - 3 weeks as a preventative
- You can use on vegetables up to harvest
Cons: Can burn plants, especially if used in full sun
Precautions: Check label and test on a small area before spraying the entire plant
Remember, just because a pesticide is considered organic doesn't mean it's not toxic. Make sure you are using the correct control for the pest you want to eliminate. Applying any pesticide late in the day will help reduce exposure for beneficials and pollinators. Always read and follow the label instructions and cautions.
Potassium Salts of Fatty Acids. Oregon State University Extension
Insecticidal Soap. Penn State University Extension
Bacillus thuringiensis (Bt). National Pesticide Information
Pyrethrins General Fact Sheet. National Pesticide Information
Botanical Insecticides. Texas A&M University Extension
Using Organic Fungicides. Purdue University Extension