A Guide to Common Organic Garden Pesticides

Organic Lettuce
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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 diseases will spread quickly. When a problem is severe enough to need control, always reach for the least toxic option first. When you need a pesticide, 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. And always follow the label directions. Even with organic products, more is not better

Keep a close eye on your garden and try to catch problems early, before they become major. 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 can very often

Insecticidal Soap

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

Pros:

  • One of the safest pesticides
  • Non-toxic to animals
  • No residue
  • You can use on vegetables up to harvest

Cons: Can burn or stress plants. Don’t use in full sun or high temperatures

Precautions: Check label for specific plants that may be sensitive to insecticidal soap

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 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. Can kill ‘good insects’ like butterfly larva Breaks down rapidly in sunlight. Can be a skin irritant

Precautions: Follow the label directions and don't overuse it

Neem

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

Horticultural Oil

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

Pyrethrins

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

Sabadilla

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

Rotenone

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

Precautions: Apply in the evening, when bees are less active

Potassium Bicarbonate

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

Pros:

  • 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 organic doesn't mean it's not toxic. Always read and follow the label instructions and cautions.