Cercospora, Cercosporidium sequoia, commonly infected junipers, cedar, Leyland cypress, Japanese cryptomeria and arborvitae, causing unsightly needle browning in the lower portion of the plant. In severe cases only the needles on the upper tips or very outside of the plant remain green. It is not uncommon, especially on Leyland cypress, for cercospora to kill the plant entirely.
Prevention is the best strategy for managing cercospora. Some combination of cultural practices and protective fungicide sprays will be most effective. Cultural practices include watering without wetting foliage during drought conditions, providing proper nutrition via fertilization and mulching to retain soil moisture. Fungicide sprays can protect newly emerging foliage from infecting spores and should be applied as new leaves are emerging. In wet climates or during moist springs reapplications will be necessary at 10-14 day intervals until conditions dry out.
Other Treatment Practices
- Adequate water is a key factor in maintaining stress free plants. A slow, deep watering event once every few weeks during dry conditions will help maintain soil moisture levels and minimize stress.
- Mulch is very beneficial for all trees because it reduces competition with turf and moderates soil temperature and moisture levels. The addition of 3 inches of wood chips or shredded bark under the drip line can have a very beneficial effect by holding in moisture and promoting healthy fibrous roots.
- Cambistat can be also be used to promote tree health and reduce the incidence and severity of stress mediated diseases and insect problems on trees growing in urban areas.
Signs of Damage
- Browning of inner, lower portions of the plant beginning in the late spring to summer
- Symptoms progress upward and outward throughout the season
- At epidemic level only the current years leaves survive
Photo: USDA Forest Service Archive, USDA Forest Service, Bugwood.org
Trees At Risk
- Rocky Mountain juniper (Juniperus scopulorum)
- Eastern red cedar (Juniperus virginiana)
- Bald cypress (Taxodium distichum)
- Arizona cypress (Cupressus arizonica), “Christmas tree plantings”
- Leyland Cypress (Cupressus x leylandii)
- Cryptomeria may also be a host
- Disease development is favored by warm, humid, wet weather and/or overhead irrigation.
- Fruiting bodies appear as tiny greenish pustules on the upper surface of needles or small twigs.
- Spores are released during wet weather in the spring and fall and are spread by air currents and wind driven rain.
- New infections occur when spores land on a film of water covering a suitable host.
Always refer to product label for rates and approved uses. Some images courtesy of forestryimages.org or Wikimedia Commons. Use of the images does not imply endorsement of treatments.