WHAT IS A RHIZOSPHAERA NEEDLE CAST

Rhizosphaera Needle Cast foliage disease. Older, two and three-year-old needles show symptoms first. As the disease progresses in the following years, newer needles will be come infected and die as well. First, the needles turn yellow and then brown. The needles drop (cast) anywhere from 3-15 months after being infected.

Hosts

Rhizosphaera Needle Cast (Rhizosphaera) is the most common disease of Spruce, especially Colorado Blue Spruce (Picea pungens) and White Spruce (P. glauca) in the Urban Landscape. Norway Spruce (P. abies) and Red Spruce (P. rubens) are much more resistant to the disease. True Fir (Abies), especially White Fir (A. concolor) and Douglas Fir (Pseudotsuga) can suffer severe damage as well.

Symptoms

  • Thinning trees with lower branch dieback.
  • Yellow and purple/brown needles.
  • Black dots (pustules) located on the underside of the needles.
  • Dropping and thinning of older interior needles

Treatment Timing and Prevention

  • Rhizosphaera Needle Cast is controlled with a spray program. (3 sprays) Spray applications are applied in the spring and early summer when new growth is elongated. (weather dependent)
  • Reduce excess moisture. Eg: sprinkler heads.
  • Increase airflow through foliage.
  • Increase sunlight on foliage.
  • Remove fallen needles

Disease Life Cycle

  • The oldest needles begin yellowing from the interior of the tree outwards throughout late fall or into the spring one year after infection.
  • Mild warm temperatures and prolonged needle wetness will favor disease development.
  • The disease enters the needles, causing infection through the needle’s stomata. (The breathing pores on the underside of the needle)
  • The new needles are susceptible all season long.
  • Fallen old needles, commonly found under the infected tree, will reinfect healthy foliage.

The spray program will control the disease and protect healthy foliage from reinfection. It will not cure the disease. This spray program is recommended as an every year maintenance program.

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