Phomopsis tip blight is one of the two common diseases of junipers and is often associated with Kabatina tip blight. Although these two diseases cause almost identical symptoms, they differ in disease development and control. Kabatina tip blight first appears in February and March whereas Phomopsis appears from April through September.
The fungus Phomopsis juniperovora infects young foliage causing damage on new growth and succulent branch tips from mid-April through September. Older, mature needles are often resistant to infection. Characteristic of the disease is the blighting that occurs about 4 to 6 inches from the tip of the branches. Prior to blighting, small yellow spots first appear on young needles. Affected foliage then turns dull red or brown and finally ash-gray with small gray lesions that often girdle branch tips. Small, black fungal fruiting bodies (pycnidia) develop in the lesions and are often observed even without the use of a hand lens.
Control measures include pruning out diseased branch tips (when feasible) during dry summer weather and when no rain or overhead irrigation is expected for several days. This will prevent the spread of the fungus into nearby areas. Select new plants that have been reported to have disease resistance to Phomopsis. When planting new seedlings, provide adequate space that will allow for good ventilation and sun exposure.
If warranted, fungicide applications on susceptible junipers include the use of copper-based fungicides (Kocide, Phyton-27), thiophanate-methyl (Domain, Fungo FLO), or mancozeb (Dithane, mancozeb, Fore) at 7 to 21-day intervals during rapid growth in the spring. However, the use of chemicals in windbreak plantings or established landscape is often not necessary.
This article originally appeared in the May 23, 1997 issue, p. 76.