You should prune out the dead wood as soon as it is visible. Another possible cause of branch die-back is phytophthora, a rot that kills the root and crown area of infected plants and can result in twigs and branches dying back. The infected trunk will have a visible vertical streak or canker. Another indicator of the presence of phytophthora is a water-soaking of the bark that looks like a dark area on the trunk near the soil line. Often, black or reddish sap may ooze from a darkened area on the infected bark.
Conditions favoring phytophthora include high soil moisture and low temperatures.
If you are watering your Japanese Pagoda adequately and the soil in which it is planted provides sufficient drainage for both monthly watering and wet winters, you should examine your tree for other symptoms that may indicate the presence of disease. Consultation with a certified arborist may be necessary for diagnosis of verticillium wilt, phytophthora or other diseases. I planted four blueberry plants. They are growing but I need help on how to manage them in the future. A. Blueberries need an acid soil and seem to do better here where they receive some afternoon shade, says UC master gardener Bill Pierce.