Question
I have an Oak tree that has been dropping excessive sap. I can't see any sap oozing from the tree. It just seems to be coming off the branches. This is the first time in 11 years that it has done this. The sap seems to be clear.The tree seems to be dropping the sap from all the branches which span about 15 to 20 feet. I live in northern California if that matters. I haven't noticed bugs of any type on the tree. It is making a huge mess on my pool and deck. Thanks for any help. Kaye

Answer
Sound like aphids or scale insects. Both will suck the plant juices from the leaves and twigs and excerete a substance called honeydews. Honeydew is high in sugar content and is sticky to the touch. Usually a black sooty mild will grow on the honeydew making everything black and sticky.

You can either spray the tree's foliage or use a systemic insecticide on the soil beneath and the tree will absorb the insecticide through the roots and take the insecticide to the leaves and twigs. Spraying a large tree can be difficult.


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)


Certain persistent insecticides that move systemically in the plant may provide control through the fall. 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.