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A Guide to Some Common Organic Garden Pesticides

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It would be nice if no pesticides were necessary in 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 a control, always reach for the least toxic option first. 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:



Neem

Ingredients: Contains 2 ingredients, azadirachtin (AZA0 and liminoids, both frm 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 mucus 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 ownNote: Baking soda or sodium bicarbonate is often recommend 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 possible 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 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.

A great way to stay on top of organic gardening practices is to subscribe to Organic Gardening (OG) magazine.

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