A. It is possible that your junipers are suffering from one or more of the diseases that cause tip dieback. Two of the most common are phomopsis twig blight and kabatina twig blight. Above-average rainfall last summer and so far this year has created a very favorable environment for these diseases.
Phomopsis twig blight is primarily characterized by tip dieback. Older growth in toward the center of the plant is less likely to be affected. The dead twigs remain attached to the plant for months. On close examination, you should be able to see small dark spots at the juncture of dead tissue and healthy tissue. Use a magnifying glass or hand lens, if necessary. These pinpoint-sized spots are the fruiting bodies that produce spores that spread the disease to healthy plants. The causal organism, Phomopsis juniperovora, overwinters on dead twigs, and infects new growth as it begins in spring. It is spread by splashing or wind-driven rain. Only succulent new growth is highly susceptible.
Phomopsis twig blight is most severe during warm, wet weather. It can cause new infections whenever there is succulent new growth on the plants and the weather is warm and wet. Repeated shearing or frequent fertilizer applications that stimulate new growth create a favorable environment for phomopsis to become severe. Control options include pruning out all of the dead twigs during dry weather and disposing of them with the trash or by burning. Do not compost severely diseased plant material. Most of us do not compost intensively enough to heat the compost pile sufficiently to kill disease-causing organisms. It is a good practice to disinfect your pruners with 70 percent alcohol and allow them to air dry between cuts, to minimize spreading the disease as much as possible.
Make fungicide applications to protect any growth forced by the pruning. If the wet weather continues, you will need to make repeated applications until the new growth has hardened off enough to become more resistant. You should also plan to make fungicide applications next spring as new growth starts. Again, you will need to make repeated applications, at intervals recommended on the label of the fungicide you choose, until the weather dries out or the new growth matures. Cleary's 3336 (thiophanate methyl) is labeled to control phomopsis twig blight.
Kabatina twig blight causes almost identical symptoms. It is caused by Kabatina juniperi. Kabatina appears to be unable to infect healthy, intact foliage. It can gain entrance only through a wound, whether from pruning, insect feeding or from winter damage. For example, if you pile shoveled snow on juniper beds during the winter, you may damage the foliage and create the entrance the disease requires.
Another difference between kabatina and phomopsis is that kabatina kills 1-year-old twigs in spring, while phomopsis kills new growth throughout the growing season. Otherwise, they are practically identical in their symptoms. Control measures are the same as recommended for phomopsis, except that Dithane (mancozeb) is labeled to control kabatina, not the thiophanate methyl recommended for phomopsis.
Laboratory analysis is required to accurately distinguish the two diseases. It is very common for both phomopsis and kabatina to infect the same plant at the same time. In that case, a spray of thiophanate methyl and mancozeb is required to protect new growth. The two products can be mixed, according to label directions, in the same spray tank and applied in one spray, rather than making two separate applications. A product called Zyban (or Duosan -- different manufacturers, different trade names, same active ingredients) contains both fungicides, but that may be difficult for home gardeners to purchase. It is available to landscape professionals, and you may be able to hire a certified pesticide applicator to make the applications for you.
Unfortunately, these diseases require monitoring and possibly spraying every year. You control or manage plant diseases; only rarely can you "cure" them. Replacing the disease-susceptible junipers with resistant varieties, or even other plants altogether that are less problematic, is a realistic option. Low-growing junipers that are resistant to phomopsis include: Chinese juniper varieties sargentii and sargentii 'Glauca', creeping juniper cultivars 'Plumosa' and 'Procumbens', and Savin juniper cultivars 'Broadmoor' and 'Skandia'.
Although no varieties are listed as being resistant to kabatina, protecting junipers from mechanical damage and insect feeding damage can reduce or eliminate problems with it.
Other evergreen options to cover the steep bank (assuming full sun and well-drained soil, conditions preferred by the existing junipers) include bearberry (Arctostaphylos uva-ursi); wintercreeper euonymous (Euonymous fortunei varieties and cultivars); moss phlox (Phlox subulata); and spreading English yew (Taxus baccata 'Repandens').
Deciduous plants (those that lose their leaves in the winter) include cranberry cotoneaster (Cotoneaster apiculatus); bearberry cotoneaster (Cotoneaster dammeri); rock cotoneaster (Cotoneaster horizontalis); willowleaf cotoneaster (Cotoneaster salicifolia); 'Goldflame' and 'Anthony Waterer' spirea (Spirea x bumalda 'Goldflame' and 'Anthony Waterer'); and Japanese spirea 'Gold Mound' and 'Shirobana' (Spirea japonica 'Gold Mound' and 'Shirobana').
First Published: July 24, 2004, 4:00 a.m.
