Tuesday, November 29, 2011

Phytophthora Root Rot on Fraser Fir

Fraser Fir: The "Cadillac" of Christmas Trees
Fraser fir is a highly desirable Christmas tree species grown in the mountains of Western North Carolina and elsewhere across the United States. As a leading producer of Christmas trees, North Carolina growers must overcome weeds, insects, and disease to produce that beautiful tree you buy on the Christmas tree lot. 
Fraser fir nursery bed where seedlings are grown up to 
5 years before transplanting to the field.  (Photo: Mike Benson)

Typical Fraser fir planting in Western North Carolina 
after about 5 to 6 years in the field. (Photo: Mike Benson)
Although growers have good management tools for weeds and insect pests, Phytophthora (pronounced fy-TOF-thor-uh) root rot threatens long-term production of Fraser fir. The pathogen, Phytophthora, produces zoospores that can swim to tree roots in saturated soil or run-off. Throughout the 11 to 15 years or more that is takes to produce a 6 to 8 foot tall Fraser fir, Phytophthora root rot is always a threat. 
Fraser fir planting that experienced Phytophthora root rot that started on trees at top of 
ridge. Over several years, trees downhill from ridge became infected and died.  
The Phytophthora pathogen produces spores that are carried in water run-off, so
the ‘wedge’ shaped area of missing trees developed in the downslope drainage 
area of the field as trees were killed by the disease.  (Photo: Mike Benson)
Fraser fir planting  after about 6 years in the field. Note patch of trees killed by 
Phytophthora root rot in far edge of field. (Photo: Mike Benson)
Lower branch ‘flagging’ may be the first indication that a Fraser fir has Phytophthora root rot.  Once the Phytophthora pathogen has infected enough of the root system that the plant can no longer transport water and nutrients  adequately, the foliage becomes yellow then turns reddish brown a short time later.  The tree will eventually die from the disease. 
Lower Branch "Flagging" (Photo: Mike Benson)
Root systems from a healthy Fraser fir transplant (right) compared to an infected 
and dying transplant (left).  Roots killed by the Phytophthora root rot pathogen 
are dark, reddish brown in comparison to root tips on healthy plants that are white. 
(Photo: Mike Benson)
Growers manage the disease by planting healthy fir transplants into fields that are well drained. Once disease develops in a tree, however, that tree is lost. Future production in that area of the field is also threatened because the pathogen survives many years in soil.

In the future, forest tree breeders and plant pathologists hope to develop a Phytophthora resistant fir with qualities equal to the Fraser fir. So when you buy that fresh cut Christmas tree this year, just remember that the Christmas tree grower was able to overcome a lot of potential problems to provide that tree for you.

For more information, click here

Special thanks to Mike Benson for writing this post!