Most likely the redwood is experiencing symptoms related to cycles between drought and rainy periods. However, if there is a significant presence of California bay laurels intermixed with redwoods, there may be enough pressure from the SOD pathogen to also cause problems on redwoods, both native and exotic. Any SOD oak infections are likely directly connected to bay laurels, as both oaks and redwoods can become infected by the large number of spores produced on bay laurel leaves. The pathogen does not move from oaks to other trees.
Leaf tip scorch symptoms on redwood trees are found from the lower to upper canopy and include healthy leaves interspersed with brown and grey leaves or portions of leaves. Grey leaves typically have black margins into the healthy tissue.
Such symptoms are typically caused by a fungus called Pestalotiopsis funerea. They are commonly associated with drought, when rainfall occurs or when there is overhead watering around the tree. Drought stress predisposes plants to being infected, so the increased moisture facilitates the infection process. Normally the fungus will only seriously affect sprouts, as branches of adult tress will regrow areas killed by the infection within a year. In nursery settings it is important to increase ventilation and avoid big differences in watering regimes to minimize symptoms.
Once bark beetles attack the main stem (trunk) of an oak, the tree is on its way out. Insecticide treatments will not save it. Oak beetles are attracted to trees that are severely compromised. They cannot attack healthy trees.
The correct approach to avoid bark beetle infestations is not to apply insecticides, but rather to identify any health issues a tree may have. As of October 2015, many trees are suffering from the prolonged drought and may need watering. Watering should be applied infrequently and never during the summer. Water-starved trees may display a thinner crown, with olive-green rather than dark-green leaves. Leaves may also be crisp when folded between your fingers. If you opt to provide water to an oak tree that is severely water deprived, make sure the water reaches a depth of about one foot below the soil surface. Also make sure the flow is low to avoid flooding the base of the tree.
