Aphids breed like crazy. One aphid can produce over 70 offspring within a week. They can destroy a plant before you even notice there is a problem. They need to be removed and removed quickly.
Tip #1. Spray the plant down with a strong surge of water. Once aphids are detached from a stem or leaf they have a difficult time getting reattached. A nozzle called a "Bug Blaster" found in most hardware stores is very effective. Blast the host plant 2 or 3 times within a few days.
Tip #2. Mix a solution of 1 cup vegetable oil, 1 1/2 cups water and 2 teaspoons of dish soap in a mist bottle. Spray directly on the plant. It will not harm the plant and will suffocate the aphids. Rinse plant after a few hours to remove dead aphids and residual spray solution. Repeat process as needed.
Tip #3. Hand squish several aphids. This releases a chemical signal to the others, warning them of eminent danger. They will drop off your plant as a result. This will not rid your plant of all the aphids, but it will slow them down.
Tip #4. Grow decoy plants such as mums, hollyhocks, or dahlias which are especially attractive to aphids. Plant these decoys away from the area you wish to protect. Add extra quick-release fertilizer to the soil to make these decoys nitrogen-rich, which aphids need to build body proteins. Under watering plants also makes the sap richer and more attractive to aphids.
Tip #5. Create a bio diverse environment. Introduce insects that are predatory to aphids. The two best insects that will devour the aphid is the Lacewing Larvae (aka aphid lion) and the baby ladybug. Both infant insects can eat aphids by the hundreds in just a few days time. Lacewings and lady bugs are sold usually in packages of 1000 for approximately $10. to $15. a package.
Tip #6. Organic sprays such as garlic, rhubarb, hot pepper and elderberry all contain Oxalic acid which is poisonous to aphids. To prevent an invasion, you can also plant garlic, chives or onions, the smell will ward off aphids.
Tip #7. Cut off colonies by simply pruning the plant where the bulk of aphids are collected. Without resorting to a more powerful insecticide you may just have to amputate a portion of the overwhelmed plant.
Tip #8. Sprinkle wood ashes over the plants. Ashes are a caustic dust and will also suffocate aphids. Use a flour sifter or coffee can with nail holes punched through the bottom, to spread. Let ashes sit for a day on the plant, then rinse with hose.
Tip #9. Use all of the above in any combination to control and kill aphids.
One time treatments will more than likely no be enough to rid your plants of the pests. Their size and prolific life cycle will require vigilance throughout the summer and harvest months.
Whatever methods of removal you choose to use, don't wait. Any evidence of aphid invasion must be controlled as soon as possible, before an infestation can develop.