Juniper Branch Death
Franklin Laemmlen, Ph.D.
A: In a word, NO! There are a number of juniper species and varieties used in California landscapes that are susceptible to a branch canker disease. This disease is caused by a fungus which invades twigs and branches. In time the twig/branch is girdled and death follows. Branch death is random in the tree or ground cover. The result is a plant which over the period of several years becomes a liability in the landscape. Control with sprays is not economically practical or effective. The plants can be pruned for a time to remove the dead tissues as they occur. However, there comes a time when the plant has lost its aesthetic value and should be removed from the landscape. I would suggest you consider something other than juniper species as replacement plants. Q: A number of twigs on my junipers are dying. The dying is mostly on the ends of small twigs. Can you help identify the problem from the enclosed samples?
A: A few weeks ago I wrote an article on cypress canker, which is caused by a fungus. This fungus can cause a twig blight. The fungus attacks and girdles the twig. At the point of the girdle the twig swells, is often rough and may have gum exuding from the bark.
The twigs you submitted showed none of the above symptoms. However, a little whittling with a sharp knife revealed that there was a tunnel under the bark of the twig. The tunnel was at the intersection of live and dead twig. I did not find an insect present, but from a review of juniper pests, I think your junipers have been injured by the "juniper twig girdler" (jtg). How’s that for an original name? The adult jtg is a small, shiny, brownish-black moth, which is active from March through May on the Central Coast. Eggs are laid singly on juniper twigs often within 8 to 14 inches of the twig tip. The young larvae tunnel into the twig and eat their way around the twig in the cambium zone under the bark. After several trips around the twig the tip flags, turns pale green to brown and dies.
There is one generation of jtg per year. Adults emerge in spring. The larvae are actively feeding during late spring and summer. Twig death usually occurs in late summer or fall. Control of this pest is difficult. The adult female is small and difficult to observe since it is nocturnal. The presence of jtg is usually first noted when juniper twigs begin to flag and die. Pruning out and destroying the affected twigs as soon as they appear may eliminate some larvae before they exit their tunnel. Make the cut into the live wood below the intersection of dying and live wood. Pruning will at least improve the appearance of your juniper, but will not eliminate all the larvae. Management of jtg is done mainly by planting jtg-resistant juniper cultivars. Tam juniper (Juniperus Sabina ‘Tamariscifolia’) is extremely susceptible to jtg damage and should be avoided where jtg is a problem. Hollywood juniper or twisted Chinese juniper (J. chinensis ‘Kaizuka’ or ‘Torulosa’) are resistant to jtg. Pfitzer juniper (J. chinensis ‘Pfitzerana’) is attacked, but in comparison with Tam juniper is less damaged by jtg.
If jtg injury cannot be tolerated, thoroughly spray the juniper foliage twice annually with pyrethroid or other broad spectrum persistent plant protection products. These sprays kill adult moths and prevent egg laying, but larvae that have already borrowed into the host will not be affected. Sprays will also not restore the appearance of damaged plants. On the Central Coast the first spray should be applied in late March and the second spray in early May. Use all plant protection products according to label directions for best results.