Juniper

Cedar apple rust and related rusts (fungi)

dormant cedar apple rust gall Cedar apple rust gall

Dormant cedar apple rust gall.

Hard, brown galls on twigs become bright orange to red with jelly-like protrusions during warm, wet weather in April and May. Some twig dieback may occur, but damage to juniper is not serious. Generally, control is not needed.

Resistant to rusts

  • Juniperus chinensis cv. Foemina and var. sargentii
  • Juniperus communis cv. Aureospica cv. Suecica and var. saxatilis
  • Juniperus sabina
  • Juniperus squamata var. fargesii
  • Juniperus virginiana cv. Tripartita.

Cercospora blight (fungus)

Uncommon in Missouri. In contrast to Kabatina and Phomopsis blights, Cercospora-infected trees will have brown foliage on the inner part of branch or close to the trunk, with branch tips remaining green. Apply Bordeaux mixture or mancozeb in late May and repeat in mid-July. The disease is found more frequently and causes greater mortality on Rocky Mountain juniper than on eastern red cedar.

Kabatina blight (fungus)

Kabatina blight

Kabatina lesions with fruiting bodies, above, and tip blight, below.

Kabatina blightYellowish-brown branch tips are evident in spring before new growth resumes. Sunken gray area at base of branch. Generally, less damaging than Phomopsis blight. Generally the damage is minimal and can be ignored. Effective fungicide programs have not been worked out, although thiophanate-methyl is labeled for the control of this disease. Timing of applications are not certain. Since it is suspected that infection occurs through wounds during the previous growing season it may be beneficial to minimize wounding in late late summer and fall. Pruning may improve appearance.

Phomopsis needle and twig blight (fungus)

Phomopsis affects newly developing needles while they are in the yellow-green stage. After foliage turns deep green, it is no longer susceptible. Infected terminals and branches fade from light green to reddish brown and finally to ash gray. The fungus can move from leaves to invade and girdle small twigs, killing the portion of the shrub above the girdled area. Disease development is favored by moderate temperatures (60 to 78 degrees F) and rain. Although blighted trees are unsightly, the disease seldom kills established shrubs. Restrict pruning to drier periods of the summer (July and August), so the resulting flush of new growth does not occur during the rainy season. Apply azoxystrobin, Bordeaux mixture or other copper fungicides, mancozeb, thiophanate-methyl or thiophanate-methyl + mancozeb once in the fall and again two or three times in the spring at two-week intervals.

Resistant to phomopsis tip blight and rusts

  • Juniperus chinensis cv. Foemina and var. sargentii
  • Juniperus communis cv. Aureospica cv. Suecica and var. saxatilis
  • Juniperus sabina
  • Juniperus squamata var. fargesii
  • Juniperus virginiana cv. Tripartita.

Spider mite feeding injury

Foliage becomes gray-green. Severely affected branches may die or become more prone to winter kill.

Update6/24/09->