Question
Is it normal to have sap falling for all of September and October from my Valley Oaks -and with our first rain yesterday, clusters of green leaves with little brown knobs around the twigs fell, some of these "little brown knobs" open and is a empty space within. These trees are at least 20,25 yr.s old -But this is the first time i can remember this happening -any comment, Thank You

Answer
Tom, The "little brown knobs"  are actually galls and are frequently attached to mature valley oaks. These "Globular Galls" are probably the source of your sap. The galls house the larval stage of a small indigenous wasp that hatches within the swollen limb. The galls are empty because the wasp have flew the coop so to speak and they are falling because the gall makes the limb structurally unsound. I would speak with a local Arborist if you are interested in controlling this problem. However I think your best bet is to live with it or remove the tree's, because I believe that any efforts to eradicate the galls would be futile. Good Luck & Happy Halloween. G