Question
We have about about 400 ft of 80 year old, well groomed privet hedge. This week we discovered 3 plants had branches totally covered with a white powdery substance.  It does not appear to have effected the leaves.  This seems strange to us.  Can you help?

Answer
This vould be a couple of things. An insect or a fungus.

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), Imidacloprid (Bayer Advanced Garden Tree and Shrub Insect Control) is a newly available systemic insecticide that can provide aphid control on trees for several months following application to the soil.  



Check with your local nursery for this. If it is small bumps along the branch covered with cottony materila is could be a cottony scale insect. These can be sprayed with the same systemic insecticide. If it  does not move it is a fungi called powdery mildew.

Powdery mildew usually is on the leaves.and twigs. Powdery mildews, as the name implies, often appear as a superficial white or gray powdery growth of fungus over the surface of leaves, stems, flowers, or fruit of affected plants. These patches may enlarge until they cover the entire leaf on one or both sides. Young foliage and shoots may be particularly susceptible. Leaf curling and twisting may be noted before the fungus is noticed. Severe powdery mildew infection will result in yellowed leaves, dried and brown leaves, and disfigured shoots and flowers. Although it usually is not a fatal disease, powdery mildew may hasten plant defoliation and fall dormancy, and the infected plant may become extremely unsightly.

To control this fungus spray the foliage with a fungicide.
Fungicides must be used to achieve acceptable control. For best results with fungicides, spray programs must begin as soon as mildews are detected. Spray on a regular schedule, more often during cool, damp weather. Use a good spreader-sticker with the fungicides. Be sure and cover both surfaces of all leaves with the spray. Fungicides generally recommended for powdery mildew control include: Triadimefon (Bayleton, Strike); Triforine (Funginex), Thiophanate-methyl (Cleary's 3336, Domain) and Propiconazole (Banner).