My conifers have needle dieback, what can I do to control the problem?
Conifers are trees or shrubs that include pines, cedars, firs, cypresses, junipers, spruces, hemlocks, larches, redwoods and yews. Most of the conifers that we typically think of are pines, junipers, cedars and spruces. Most of these plants also struggle in the central part of Oklahoma due to clay soils, drought/excessive moisture and the heat. These factors can stress conifers. When the trees or shrubs get stressed, they are more subject to insect damage or disease. You can reduce the stress by fertilizing at least once a year and providing deep moisture when rainfall is inadequate. Avoiding or supplementing clay soils is also helpful if you want to enjoy your evergreen.
In central Oklahoma, long needle pines are primarily infected with Diplodia (Sphaeropsis) tip blight or Dothiostroma needle blight. Treating with liquid copper in April and May will help control the problem. Junipers (including Arborvitae) can be infected with members of Mycospharella or Phomopsis. Both can be treated with liquid copper. Junipers can also develop a disease called Seiridium canker. This disease has oozing wounds below the dying material. There are no chemical controls for this disease. Resistant hosts should be planted. If a pine tree dies suddenly, it is likely due to the pine wilt nematode that is carried by the pine sawyer beetle.
For more information contact the OSU Extension Center, 14001 Acme Road, corner of MacArthur and Acme Road in Shawnee or 273-7683.