Aphids prefer moderate temperatures with a little bit of moisture. Hot summers can retard their growth and damage. When aphids feed, they produce honeydew, which is a substance that can become so thick that it drips from the trees and plants, Goodspeed says. People often tell me that their tree is 'bleeding' sap, because this honeydew is dripping on their car, picnic table, children and slow-moving pets. Honeydew is just a sugar-water substance, and is not toxic to plants or the people it drips on.
Aphids suck and feed on the sap of their host.
If left unchecked, the leaves they feed on begin to curl, providing the little pests a nice protected area where they can continue to feed uninterrupted. Severe infestations cause leaves to yellow and drop, Goodspeed says. Normally they only weaken the plant, and do not severely damage trees or other woody plants, or cause them to die. The most common and easiest aphid control method is restraint. Be patient and allow the natural enemies to come and make a meal of them.