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Juniper Blights

Phomopsis blight is the most common tip blight of junipers in the Midwest. Most damage occurs on eastern red cedar and on creeping, Rocky Mountain, and savin junipers. Still, you may see the fungus on arborvitae, white cedar, cypress, Douglas-fir, fir, yew, and larch, as well as junipers. The newest growth is susceptible to infection and becomes resistant once needles become a normal, dark green. Infection occurs on the youngest needles, starting as yellow spots. Shoot tips then turn light green and finally brown. However, the first symptom usually seen by a homeowner is the reddish brown color of shoot tips. A grayish band is often visible at the base of the dead shoot, and 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. Occasionally a stem canker is also found in association with this disease.

Infection by Phomopsis can occur when succulent new growth is present in wet weather. The fungus is also very persistent. Spores germinate under moderate temperatures (60 to 82 degrees F) and high humidity within seven hours after coming into contact with the new foliage. If the foliage dries before infection occurs, the spores are not killed; they begin growth again with wet weather. Pycnidia form three to four weeks after infection. Spores are dispersed by splashing rain. Watch for this disease soon.

If tip blight symptoms occur in the spring, but before new shoot growth has begun, then Kabatina blight is the most likely cause. This fungus was present last summer, formed fruiting bodies from February to May, and is evident in the spring on one-year-old twigs. Kabatina requires wounding for infection to occur.

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 your planting 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. Pruning is a form of wounding and may increase the chance of infection with Kabatina, but by pruning in dry weather this risk will be lessened. Fungicide recommendations are provided in the Illinois Commercial Landscape and Turfgrass Pest Management Handbook, 1998-1999, as well as the Illinois Homeowners’ Guide to Pest Management. Report on Plant Diseases No. 622 contains more details about Phomopsis blight.

Author: Nancy Pataky


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