Every year I notice these little green insects. Well, sometimes they aren't green, I've seen them in orange and yellow and they come in red, brown, and black too. Whatever fashion sense these insects display one thing is for sure: you don't really want aphids on your plants! Aphids are a soft-bodied insect that love to suck on the juices of plants. New foliage is especially vulnerable to an infestation and as you can see so are tulip petals. While the sucking damage aphids cause may not be serious, aphids can spread diseases. Fortunately aphids are easy to remove without harsh chemicals.
Method 1: Water
Spray the aphid infected plant with water from a hose. It will knock off the aphids. Make sure to spray the undersides of leaves as that is one of their favorite places to lurk.
Method 2: Wipe them out!
Take a wet paper towel and wipe down the aphids to remove them from your plant.
Method 3: Introduce a predator!
This isn't as scary as it sounds. No lions, tigers, or alien creatures are necessary. Ladybugs however, are perfect! The larval stage of the lady bug (which looks like a little teeny tiny alien alligator) is a voracious aphid eater. Look around your garden and you'll probably find one like in this picture. Move it to your aphid infected plants and let it satiate its appetite. Parasitic wasps and lacewings are also great friends to have around!
Method 4: Insecticidal soap
Insecticidal soap will take care of aphid infestations. Repeat applications may be necessary.
Method 5: Neem Oil
Neem oil is made from the neem tree and will help to eradicate aphids.
Both the neem oil and the insecticidal soap may hurt predator insects so inspect your plants for their presence before spraying and remove predator insects if you find them. Although if you do find them you probably don't need the spray! Always try the least invasive method of control first and attempt Methods 1-3 before resorting to sprays.
For a little more on aphids including details on their life-cycle read this post I wrote back in 2008.