Phomopsis and Kabatina are two common fungal pathogens affecting Illinois junipers. Both cause fruiting structures that appear similar through a hand lens. |
Juniper tip blight, or Phomopsis blight, is caused by a Phomopsis species. It is the most common disease of Midwest junipers. Most damage occurs on eastern red cedar and on creeping, Rocky Mountain, and savin junipers; but we have seen the fungus on arborvitae, Douglas-fir, fir, yew, and larch. The newest growth is susceptible and becomes resistant once needles become a normal, dark green. Growth now emerging is susceptible. Plant development is ahead of schedule this year, so some areas of the state may have already passed through the susceptible stage. Phomopsis infection occurs on the youngest needles, starting as yellow spots. Shoot tips then turn light green before becoming brown. Homeowners usually dismiss early symptoms as winter burn and do not become concerned until brown shoot tips appear. One diagnostic clue is a grayish band at the base of the dead shoot. In this band are pinheadsized, black, fruiting bodies (pycnidia), visible to the naked eye or with a hand lens. If the tissue is very dry, place it in a plastic bag with wet paper toweling overnight; the fruiting bodies will be easy to see the next day.
Infection by Phomopsis can occur when succulent new growth is present in wet weather. The fungus is very persistent. Spores germinate under moderate temperatures (60 to 82 degrees F) and high humidity within 7 hours after coming into contact with the new foliage. If foliage dries before infection occurs, the spores are not killed; they begin growth again with wet weather. Pycnidia form 3 to 4 weeks after infection. Spores are dispersed by rain. Watch for this disease soon. If you had problems before, consider a protective fungicide.
Phomopsis blight may be controlled by pruning and removing infected foliage when the plant is dry and by using preventive fungicides. If you are willing to start over from scratch, use resistant varieties for the easiest long-term control. If replanting is not an option, then pruning is important because the most common source of the fungus is infection from the previous year. Prune only dry foliage to avoid spreading spores and to lessen the risk of infection by other fungi. Fungicide 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, contains more details about Phomopsis blight. This report is available in Extension offices or on the VISTA Web site.
Kabatina blight is the other common Illinois juniper blight. It is caused by a fungus that looks similar to Phomopsis unless you look at fruiting bodies with a microscope. The significant difference in the diseases is time of symptom development. Phomopsis blight occurs on new growth, with infection occurring this spring. Kabatina blight occurs on last yearís needles. You might see it in March or April on what you believe is the new growth. That is actually last yearís growth. This yearís is much lighter in color, emerging 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 control. It is important to remove and destroy infected twigs in dry weather. 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 Johnsonís book, Diseases of Trees and Shrubs.