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Juniper Blights

June 5, 2002

Most gardeners and landscapers are familiar with juniper blight from Phomopsis. At this time, however, another, closely related fungus might be the problem: Kabatina. It is important to understand the differences between these fungi because Phomopsis can be managed, but we have fewer choices with Kabatina.

Juniper tip blight, or Phomopsis blight, is the most common disease of Midwest junipers. Most damage occurs on eastern red cedar and on creeping, Rocky Mountain, and savin junipers; we have seen it on arborvitae, Douglas fir, fir, yew, and larch. The newest growth is susceptible, becoming resistant once nee-dles become dark green. Emerging growth is susceptible, but you won't see symptoms for a few weeks.

Phomopsis infection occurs on the youngest nee-dles, starting as yellow spots. Shoot tips turn light green, then brown. Homeowners usually dismiss early symptoms as winter burn and do not become concerned until shoot tips brown. A diagnostic feature to help identify this disease and distinguish it from wea-ther scorch is the grayish band at the base of the dead shoot. In this band are pinhead-sized, black fruiting bodies (pycnidia) of the fungus. They are visible to the naked eye or with a hand lens. If the tissue is dry, place it in a plastic bag with a wet paper towel over-night. Fruiting bodies will be easy to see the next day.

Infection by Phomopsis can occur on succulent new growth in wet weather. Spores germinate under moderate temperatures (60° to 82°F) and high humidity, within 7 hours of contacting the foliage. The fun-gus is persistent. If foliage dries before infection occurs, spores do not die; they begin growth again with wet weather. Pycnidia form 3 to 4 weeks later. Watch for this disease soon.

Splashing rain disperses spores. Phomopsis blight may be controlled by pruning and removing infected foliage when the plant is dry and by using preventive fungicides. If replacing plants, use resistant varieties for the easiest long-term control. If replanting is not an option, pruning is important because commonly infection is from the previous year. Prune only dry foliage to avoid spreading spores and to lessen the risk of infection by other fungi. For fungicide recommendations, see the Illinois Commercial Landscape and Turfgrass Pest Management Handbook and the Home, Yard, and Garden Pest Guide. Report on Plant Disease (RPD) no. 622, describes Phomopsis blight and is available at . http://www.ag.uiuc.edu/~vista/horticul.htm

Already in 2002, the Plant Clinic has received several samples of Kabatina blight, the other juniper blight. It is caused by a fungus that appears similar to Phomopsis unless you look at fruiting bodies with a microscope. The significant difference in these dis-eases is the time of symptom development. Phomop-sis blight occurs on new growth, with infection the same spring. Kabatina blight occurs on last year's needles. It usually follows a wound such as winter injury. You might see it in March to May on "new" growth--actually last year's growth; this year's growth is much lighter in color and emerges in May and June.

The other significant difference is management. Kabatina blight is not clearly understood, and fungicide timing has not been effective. Remove and de-stroy infected twigs in dry weather. Reports indicate that disease-resistant varieties are in development, so ask for these at your nursery. For information about Kabatina blight, see Sinclair, Lyon, and Johnson's book, Diseases of Trees and Shrubs.

Author: Nancy Pataky


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