Why Douglas Fir Losing Needles - Knowledgebase Question

Canton, MI
Avatar for chuckhayes
Question by chuckhayes
March 9, 2010
What is the cause and how can I prevent my evergreen from losing needles? It is about 10 fooet tall and has lost 50% of it's needles. The tree is almost 3 years old. I live in Canton.

Answer from NGA
March 9, 2010
Drought stress is a possibility, but there are two diseases associated with needle cast and several insects that can cause the same problem. I can't diagnose your tree without examining the needles but here's what to look for:
Rhabdocline Needlecast
Current years needles develop small yellow spots in late fall or early winter. Yellow spots enlarge and needles appear mottled. By spring the needle spots are a yellowish brown to reddish brown. Sometimes spots coalesce to discolor the entire needle. The discolored needles are cast in the spring after spore discharge.

Swiss Needlecast
Foliage symptoms include yellowing and browning of needles in late fall of the first year or during spring and summer of second year. Symptoms are most severe on older needles on lower branches. Diseased needles are often uniformly brown at the tips, but never mottled. infected needles are usually cast during late fall and winter.

Although fungicide applications can control the disease, a tree that is 50 per cent involved my not recover.

For positive diagnosis, take samples of the needles (alive and dead) to your local cooperative extension office: Wayne County Extension, 640 Temple Street, 6th Floor
Detroit, Michigan, 48201-2558 Phone: 313-833-3412.

Good luck with your tree!

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