Brad Withrow-Robinson, Forestry and Natural Resources Extension agent for Benton, Linn and Polk Counties and Amy Grotta Forestry and Natural Resources Extension agent for Columbia, Washington and Yamhill Counties

Black stains may be found by cutting into sapwood with an ax

We recently attended a field tour on Black Stain Root Disease in the Coast Range. The tour was organized by Dave Shaw and Klaus Puettmann (OSU Extension and College of Forestry) and was attended by private land managers, forest health specialists and researchers from state and federal agencies.

Black stain root disease (BSRD) is a native root disease affecting several species across the West, but attacks mainly Douglas-fir in western Oregon. Foresters are aware of several “hot spots” where the disease has been particularly active in recent years, and there is concern that it might be expanding.

The purpose of the tour was to share and compile the field observations and experiences of the participants to test the perception that the disease is expanding in scope or severity and consider management responses. We of course wanted to figure out how that might affect family forest landowners in our area.

BSRD causes a gradual or rapid decline and crown discoloration of infected trees.  Older trees generally do not quickly succumb to the disease. It forms disease centers that gradually spread, much like the symptoms of other root diseases like laminated root rot.

Tree on left shows abrupt change in growth and color typical of BSRD

 

But BSRD is most visible and important in young trees, especially precommercially thinned plantations.  Young trees often show an abrupt change in condition from healthy vigorous trees one year, to stunted and yellowing trees the next year. A characteristic of BSRD.  The disease is named for the black or dark purple staining of the sapwood.  It can be by hacking into the stem (something all pathologists love to do) or in cross section.

BSRD has two means of spreading. This includes root to root contact, as with many other root diseases.  But black stain can also be moved by several pests that are attracted to stressed or damaged trees, such as insects and forest pathologists.  Insect vectors seem to be how it moves from an existing disease center to create new infections.  This creates the potential to spread, and to be affected by management activities that damage or stress trees.  This includes road building, “brushing” roads  (mechanically clearing road edges) and young stand thinning. Young stand thinning is seen as the management activity with the greatest potential to increase this disease.  This is because the insect vectors (weevils and a root bark beetle) are attracted to cut stumps.   The insects infect the stump, and the fungus can then spread to neighboring trees through root contact and grafts.   Activities causing soil disturbance and root damage are also likely to invite spread.

Take Home Message

Our sense at the end of this tour was that BSRD is not something for most family forest landowners in NW Oregon to be very concerned about. It is out there, but not in high concentrations in most areas.  The general consensus of the group was that the recent rise in the visibility of BSRD is mostly due to the gradually shifting pattern of age classes on the landscape that is making the disease more evident, and not a significant expansion of its range or activity.   It is and is likely to remain a much less-significant disease in our area than laminated root rot.    That said, those who are in an area with a significant amount of BSRD do need to pay attention when harvesting and establishing new plantations.  You can find out more about BSRD at these links:

https://www.forestpests.org/acrobat/bsrd.pdf

https://www.fs.usda.gov/Internet/FSE_DOCUMENTS/stelprdb5187236.pdf

 

The symptomatic black stains are irregularly distributed in sapwood, as seen in stump
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