Twig blight of horizontal varieties of juniper, particularly "blue rug" types is a common problem. Phomopsis twig blight may also cause a more rare die back of branches on eastern red cedar (Juniperus virginiana), arborvitae (Thuja occidentalis), yews (Taxus), fir (Abies), Douglas fir (Pseudotsuga menziesii), larch (Larix), hemlock (Tsuga) and certain cedars.


Symptoms include the die back of the tips of branches that are equal to or smaller than the thickness of a pencil. Infected foliage becomes pale, then reddish brown and then turns brown or ash-gray after death.

To confirm the diagnosis of Phomopsis as the cause of the twig die back, scrape away the thin bark until you reach living wood. There should be a sharp line between the discolored dead wood and healthy wood. Also, look at the base of the ash-gray colored scale needles for small, black fruiting bodies.

These fruiting bodies form the spores that cause new infections. In wet weather, spores ooze from the fruiting bodies and splash onto new foliage. The spores are produced year around and infect yellowish green juvenile tissue. The darker green mature foliage is resistant to infection.

Junipers generally have two flushes of growth under natural conditions, one in late April through June and another in late August to September. When growth coincides with wet, warm weather or frequent overhead watering, disease can be severe.

Most severely diseased plantings are the result of excessive wetness. This may be due to the site being poorly drained, shaded or over watered by irrigation. Under continuously wet conditions, an entire plant may die.


The major way of preventing twig blight is to plant Juniper species that are not susceptible to the disease. See the list below.


Prune out and destroy infected branches by cutting them back to where the live tissue exists. Plant susceptible species in areas with good air circulation and avoid overhead watering early in the day. Full sun sites are usually less of a problem because this helps the foliage to dry faster after rains and irrigation.

Chemical control would involve spraying a fungicide labeled for control of Phomopsis at budbreak in the spring and repeated at 10 to 14 day intervals until the new growth had matured to a dark green.

Note: We have provided some general information and observations on this topic aimed at the home gardener. Before you take any serious action in your landscape, check with your state's land grant university's Cooperative Extension Service for the most current, appropriate, localized recommendations.


The best approach to avoiding future problems is to plant resistant types of junipers. Those reported as resistant to Phomopsis twig blight include:

Whatever you plant, be sure to place it in as much sun as possible and choose a site with excellent drainage.   

 

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