They provide food for many small insects and other invertebrates.
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Aphids are small (less than 1/4 inch long), soft-bodied insects that suck sap from leaves, twigs, or roots. Depending on the species and the plants they feed on, they may appear:
They are pear-shaped insects with long legs and antennae. Adult aphids can be winged or wingless. They are often clustered on new growth.
Although aphids are most common in spring and summer, some species mate and produce eggs in fall or winter, which provides them a more hardy stage to survive harsh weather. Under ideal temperatures, many aphid species can complete their life cycle in less than 2 weeks, and because of their prolific reproductive capacity, enormous populations of aphids can build up in a short time.
There are many thousands of species of aphids around the world. Aphids are plant specific and do not transfer from one type of plant to another. There are rose aphids, birch aphids, and the list goes on. Anywhere there are plants there are aphids.
Aphids have a life span between a few weeks and a few months.
Although aphids seldom kill a plant, the damage and unsightly mold growth they cause sometimes warrant control. Aphids cause curling, yellowing, and distortion of leaves and stunting of shoots. In urban environments, aphids can produce copious amounts of “honeydew” excretion, which often turns black with the growth of a sooty mold fungus. Sooty mold is usually just unsightly, coating leaves with a black residue, but can kill a small tree that is already under stress.
Check plants frequently for aphids, including the undersides of leaves. Look for curled green leaves and/or wilted buds. Many species of aphids cause the greatest damage when temperatures are 65 to 80 degrees Fahrenheit. The presence of ants often indicate aphids, because ants act as “farmers,” protecting the aphids, in order to harvest their honeydew excretions.
First, ask yourself if the impact they cause warrants getting rid of them. If there is little damage, some aphids are okay. Even in our urban environment, aphids have natural predators (such as lady bugs) that will keep the population under control. We actually want some aphids in order to sustain the predators so they can reproduce to eat more aphids! The key here is not to panic if a few aphids are feeding on a tree.
A heavy rainfall usually reduces aphid population. If there is no rain in the forecast, the easiest thing to do is to wash off the aphids with a strong jet of water one morning per week (morning is best, allowing the leaves to dry during the day). Doing it more than once a week helps keep the population down. You can wash leaves when you’re watering your young tree, washing your car, or watering plants.
If aphids are causing sufficient damage to warrant further treatment, or if washing with plain water has not worked, we suggest one of two insecticides. Always follow manufacturer’s application instructions:
Keep in mind, using a broad spectrum insecticide will kill ladybugs, lacewings, parasitic wasps, and other beneficial insects that feed on aphids.