Question
Hello,
I've noticed something that resembles cotton on the leaves of my oak tree.  It is not on the bark or branches.  Just the low-lying leaves.  Can you tell me what this is and if I need to get rid of it?

Answer
Sounds like cottony aphids, an insect.
Check and see if there is movement when you touch the cottony stuff. If so these are insects. There also should be some stick liquid on the leaves caused by the insect sucking the plant juices. IF so.
Chemical Control - Contact Insecticides Numerous contact insecticides are registered for aphid control. Since aphids are often placed under considerable pesticide pressure in field crops and greenhouses, they may be resistant to certain categories of insecticides. Therefore, if you do not obtain reasonable control, consider rotation to another insecticide. Contact insecticides currently registered for aphid control include: acephate (Orthene),  bifenthrin (Talstar), chlorpyrifos (Dursban), diazinon,  malathion, nicotine sulfate, pyrethrum, rotenone, resmethrin, and tetramethrin + sumithrin.


Chemical Control - Systemic Insecticides Several systemic insecticides are useful in aphid control. Aphids have sucking mouthparts and are thus very susceptible to pesticides located in the plant vascular system. Some of the systemic insecticides also have contact activity. Systemics injected or applied to the ground are less harmful to beneficial insects. Systemic insecticides include: acephate (Orthene),