Is soapy water effective against aphids?

Soapy water is effective against aphids because it quickly breaks down the protective wax coating of the aphid, causing rapid dehydration. It is best to use pure castile soap with no other solutions added. I have successfully controlled aphid infestations on roses utilizing this technique. It will work best when the solution is applied at the correct concentrations.

Temperature control keeps plants safe. Under no circumstances should you spray when the temperature exceeds 85°F (29°C). Heat will burn the leaves from the soap. I monitor forecasts for every application! It is best to apply soap in the early morning, and you can rinse any residue before the midday heat sets in. The earliest morning application was most advantageous for very tender plants such as basil and mint.

Precisely diluting the solution is essential. Too much soap will harm plants; not enough won't kill the aphids. I use a measuring spoon every time I make the solution. If it is a sensitive plant, like a fern, I will cut back to about 1 tablespoon per quart. Always shake the mixture well before spraying!

Combine soap with additives for problematic infestations. Add 1 tsp of neem oil per quart of soap, or for an extra punch, the extracts of garlic or pepper (be careful - I do not use these on edible plants). However, be sure to rinse them off within 2 hours.

Observe plants after treatment. It's important to watch for any soap residue or leaf curling. In healthy plants, you will notice a positive change within twenty-four hours. The aphids will turn brown and fall off. If you see new pests, retreat the plants at the next cycle, which is in forty-eight hours. I keep a record of the results to refer back to when creating mixtures in the future.

Read the full article: How to Control Aphids: Proven Methods Guide