Best thing for aphids and other insect pests is to have healthy plants and an abundance of predators. |These include wasps, ladybeetles, mantids, birds etc.

Ensure your plants are getting their fair dose of potash in the organic fertilisers you use and lay off the high nitrogen ferts. Potassium builds plant cells and toughens leaves, making them unpalatable to pests. They may still get hit when younger but the pests will quickly move on.

You can remove aphids with a jet of water from the hose or a by squishing them in your fingers.

Building a healthy ecosystem that encourages predators may not happen in one season. If you used insecticides in the past, these predators would have been thinned out too. The pests will always come back faster than the predators. To assist, you can plant winter flowering plants that will feed the predators thru winter, to allow them a headstart next spring.
Avoid insecticides. Use organic control methods.
Here's a website that suggests a few control methods.
http://www.greenharvest.com.au/pestcontrol/aphid_intro.html

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The secret is the soil.

Back, found something else that might be useful to you while I was cleaning up my site. Hope this can help you.

INSECTICIDES:

The ultimate organic Insect Killer and Repellant
Ingredients:

Chopped peel of 1 citrus fruit (orange or lemon)
4 cups of boiled water
1 entire bulb of garlic
1 smallish onion
1 tbsp hot pepper (flakes, powder or fresh)
Thin strainer
Funnel
Spray bottle
Directions:

1. Steep the all your ingredients overnight in the boiling water.

2. Pour the whole mess into a blender or food processor and liquefy.

3. Strain through cheesecloth ,a thin-meshed strainer, or a coffee filter placed inside a funel. Be sure to capture all the particles to avoid clogging your sprayer.

4. Funnel the liquid into a spray bottle.

How to Use:

Thoroughly coat the leaves of the infected plant with the spray. Be sure to get the undersides and other nooks and crannys where bugs will hide. Store your mixture in the fridge to avoid the rotting smell that will eventually arise.

Why It Works:

Garlic contains a chemical that bugs don't like. As an added bonus it also has fungicidal properties that may aid or prevent some diseases. The active ingredient in hot pepper is capsicum. This is the stuff that burns your eyes. Some rodents will also be repelled by hot peppers. And the citrus burns soft bodied insects...kind of how citrus juice burns your eye.

Dormant Oil Spray
Dormant oil is a nontoxic spray to control sucking and chewing insects in the egg stage before they can do any damage. Use dormant oil on trees, shrubs and evergreens in early spring while they are still dormant, before buds develop. You can buy the spray from any garden supply store or make your own from mineral oil and soap using the following recipe:

1 gallon mineral oil
1 pound oil-based soap
1/2 gallon water

Combine all ingredients, boil, and mix very well. Dilute 1:20 with water and use immediately because the ingredients separate quickly.

Spray on a day when the temperature is above 40 degrees and you are not expecting a freeze for at least 24 hours. Drench the branches of your shrubs and trees thoroughly - it's impossible to overdo it.

For citrus trees, you should buy a special dormant oil from your garden supply store. Citrus leaves can be damaged by the film that remains on the leaves.

From GardenGuides.com

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LadyBugs by the dozens... you can get them at most garden centers or also online for a really reasonable price. 1500 of them for $5.95 If you and your neighbors yard are infested, I would recommend you get at least 3000 of them. You really should spread ladybugs BEFORE you use that nasty ol chemical stuff! Just a suggestion! There are many other places online to get them but I have done business with the one I linked to you and seemed to have good luck and quick delivery! Hope this helps you!

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See Ya in the Garden!