Junipers in Illinois are plagued by rusts, Kabatina blight, and Phomopsis blight. The rusts were discussed in issue no. 2. This article focuses on the difference between the two fungal needle and stem blights.
Phomopsis blight is the most common disease of juniper. It 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. Kabatina blight is a secondary invader on wounded plants. It usually follows winter injury and appears in early spring, before the new growth. Fungicides are not useful against Kabatina blight.
Juniper tip blight is also known as Phomopsis blight. The newest plant growth is susceptible to infection and becomes resistant with age, usually once needles become a normal, dark green. Infected shoot tips turn light green before becoming brown. One diagnostic clue is the presence of a grayish band at the base of the dead shoot. In this band are pinhead-sized, 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 tissue is very dry, place it in a plastic bag with wet paper toweling overnight. The fruiting bodies are easy to see the next day.
Management of Phomopsis blight includes pruning and removing infected foliage when the plant is dry, using resistant varieties, or using preventive fungicides. Prune only dry foliage to avoid spreading spores and to lessen the risk of infection by other fungi. Fugicide recommendations are provided in the 2003 Illinois Commercial Landscape and Turfgrass Pest Management Handbook, as well as the Home, Yard, and Garden Pest Guide. Report on Plant Disease, no. 622, “Phomopsis Twig Blight of Juniper,” is available in Extension offices or on the Web at http://www.ag.uiuc. edu/%7Evista/horticul.htm.
Kabatina blight is the other common Illinois juniper blight. It is caused by a fungus that appears very similar to Phomopsis. The significant difference in these diseases is the time of symptom development. Phomopsis blight occurs on new growth, with infection occurring in the spring. Kabatina blight occurs on last year’s needles. You might see it on your junipers in March or April on what you believe is new growth. That is actually last year’s growth. This year’s growth is much lighter in color and emerges in May and June. Kabatina continues to affect old growth or injured growth during the growing season.
The other significant difference in these diseases is management. Kabatina blight is not clearly understood, and fungicide timing has not been effective in disease control. It is important to remove and destroy infected twigs in dry weather. Also try to assess and relieve any site stress. Reports indicate that disease-resistant varieties are in development, so ask for these at your nursery. Some information about Kabatina blight can be found in Sinclair, Lyon, and Johnson’s book, Diseases of Trees and Shrubs.