BROOKS TREE CARE
When should I have my trees pruned?
There are no concrete dates for tree pruning, but there are some guidelines. In general you can be sure that pruning after the first crisp days of fall are a safe time to prune most trees. However there are exceptions, for instance, it is not recommended to prune Coast Live Oaks in the wet seasons in order to avoid spreading spores of Phytopthera (SODS).* Conversely, you should only prune Pines during the wet months to prevent the infestation of Pine Beetles. Both of these examples are subject to other considerations that could trump the risk of pruning during the less optimal pruning time. The season for pruning trees located near the coast is often year long. Heavy cuts on a stressed tree can lead to it's death regardless of season. An Arborist should advise you on pruning timing with a reasoned discussion taking into account all the factors that effect the tree. The fact you called him/her does not mean it is an optimal time to prune.
*Amended 11/14/12: Latest information does not support the recommendation to avoid pruning Live Oaks in the wet season.
"It is better to properly prune a tree in the wrong season, than to improperly prune a tree in the correct season"