blue spruce - Knowledgebase Question

Bowdoinham, Ma
Question by catsass2856
March 21, 2010
every feb. it looses its needles,this has been for the last 3 years, any idea what is causing it ? or shoule i cut it down.( don't want to) its about 20 yers old. puts out new needles every spring. thank you , deb

Answer from NGA
March 21, 2010


Rhizosphaera needle cast, a fungal disease caused by Rhizosphaera kalkhoffii, can attack blue spruces. Symptoms of the disease are discoloration of the needles, needle drop, and eventual defoliation. Infected needles turn yellow in July and then reddish-purple in August. The needles eventually turn brown and fall off one to several branches. A severely affected tree will have many bare branches. Premature needle drop is the primary damage, causing the tree to become unsightly. However, branches that are defoliated for four or five years may die. If left uncontrolled, the disease can eventually kill the tree.

The disease is spread primarily by rain water splashing the spores from infected needles to newly emerging needles in the spring. Pycnidia emerge from these newly infected needles the following spring to start a new disease cycle.

Cultural controls that help prevent disease spread include promoting good air circulation in and around trees by proper plant spacing and pruning, and mowing grass and removing brush from around trees. Pruning shears should be sterilized with alcohol (70% isopropyl alcohol) between cuts and between trees.

If trees are infected, fallen needles should be cleaned up and discarded in a sealed plastic trash bag and sent to the dump. If a blue spruce tree is in such bad condition that the owner wants to replace it, a tree species other than spruce should be considered, so the new tree doesn't succumb to the same disease.

Fungicides can also be used as part of a management program. Infected trees can be sprayed with bordeaux mixture 8-8-100 (8 lb hydrated lime, 8 lb copper sulfate, 100 gal water) or chlorothalonil fungicide. Fungicides should be available at local nurseries, garden supply stores, or feed stores. Fungicides provide protection against infection and prevent spread of the disease within the tree. They should be applied to the tree when the new needles are half developed and again when they are full length.

Best wishes with your spruces!

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