Juniper tip blight, a progressive dying back of twigs and branches, can be caused by one of three fungi, Phomopsis juniperovora, Kabatina juniperi, or Sclerophoma pythiophila. These diseases are devastating to young trees and hedges; trees more than five years old are less seriously damaged. In addition to many species of juniper, arborvitae, white cedar, cypress and false-cypress are susceptible to P. juniperovora. K. juniperi infects juniper species primarily, but S. pythiophila infects needles of pines, Douglas-fir, and eastern larch, and twigs of juniper.
Blight symptoms first show up on recent growth of the lower branches. Dieback begins with shoot tips, and progresses back toward the main stem (Fig. 2). Death of the entire plant may result where P. juniperovora and/or K. juniperi infections are involved. S. pythiophila infection often follows winter injury, but usually doesn’t kill whole plants. Drought, freezing, dog urine, and transplant shock can cause similar dieback symptoms. However, if fungi are the cause, they will produce small black fruiting bodies (up to 0.5 mm in diameter) on recently killed leaves (Fig. 1) and stems and thus aid in diagnosis of juniper tip blights.
P. juniperovora, K. juniperi and S. pythiophila overwinter in killed twigs and bark on the shrub or on the ground. Fruiting bodies of the fungi develop in the spring and, during wet weather, release many spores capable of causing new infections. P. juniperovora attacks young succulent shoot tips and may also enter the plant through wounds. Infections can occur throughout the summer. K. juniperi attacks one year old growth in the fall, with symptoms showing up in early spring. The fungus may enter the plant through wounds, as well. If wet weather prevails, these fungi will spread throughout the shrub in the course of a few years or less. S. pythiophila attacks shoots weakened by winter injury.