Juniper tip blight is caused by a Phomopsis species, but not the same species that causes galling on many woody hosts. Tip blight is the most common disease of junipers in the Midwest. Most damage occurs on eastern red cedar and on creeping, Rocky Mountain, and savin junipers, but you may also see the fungus on arborvitae, white cedar, cypress, Douglas-fir, fir, yew, and larch. The newest growth is susceptible to infection and becomes resistant when needles become a normal, dark green. The growth that is now emerging is susceptible to this fungus. Infection occurs on the youngest needles, starting as yellow spots. Then, shoot tips turn light green and finally brown. Homeowners usually don’t notice the problem until the appearance of reddish brown shoot tips. A grayish band is often visible at the base of the dead shoot, and pinhead-sized, black fruiting bodies (pycnidia) of the fungus are found in this band. 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°F to 82°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, and spores are dispersed by splashing rain. Watch for this disease soon.
Phomopsis blight can 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, 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 Illinois Commercial Landscape and Turfgrass Pest Management Handbook, 1998–1999 and in the Illinois Homeowners’ Guide to Pest Management. Report on Plant Disease No. 622 contains more details about Phomopsis blight.