Juniper tip blight (also called Phomopsis tip blight) commonly affects new growth on junipers. It may also appear on arborvitae, white cedar, and baldcypress. In Illinois, infection begins in May, so start watching new growth for symptoms. Phomopsis blight causes the tips of new growth to turn brown and die. This disease is common in warm, wet weather as we have experienced in much of Illinois the last few weeks. It can be controlled with fungicides and resistant varieties.
The newest growth on a juniper is susceptible to infection and becomes resistant with age, usually once needles become a normal, dark green. Following infection, shoot tips turn light green, then brown. One diagnostic clue is the presence of a grayish band at the base of the dead shoot. In this band are pinheadsized, black, fruiting bodies (pycnidia) of the fungus. The pycnidia are visible with the naked eye or with the aid of a hand lens. If the suspect tissue is very dry, place it in a plastic bag with damp paper toweling overnight. The fruiting bodies will be easy to see the next day. Waiting several days will yield all sorts of interesting secondary fungi but will make diagnosis more difficult.
Management of Phomopsis blight includes pruning and removing infected foliage when the plant is dry, using preventive fungicides, or using resistant varieties in new plantings. It is also helpful to space plants to allow good air movement around plants and to provide adequate but not excessive fertilization. Prune only dry foliage to avoid spreading spores and to reduce the risk of infection by other fungi. Avoid excessive pruning or shearing in the spring or fall when infection could occur. Fungicide recommendations are provided in the 2005 Illinois Commercial Landscape and Turfgrass Pest Management Handbook, as well as the Home, Yard, and Garden Pest Guide. Fungicides are applied in the spring and fall for best disease control. Report on Plant Disease, no. 622, “Phomopsis Twig Blight of Juniper,” contains more details about Phomopsis blight. This report is available in Extension offices or on the Web at http://www.ag.uiuc.edu/%7Evista/horticul.htm.
Other juniper problems that can mimic Phomopsis tip blight include fertilizer burn, drought stress, root injury and Kabatina blight. Kabatina blight is caused by a secondary fungal invader on wounded plants. It usually follows winter injury and appears in early spring, before new growth has appeared. Fungicides are not useful against Kabatina blight.