Incense Cedar browning a lot this year

Asked August 26, 2019, 12:24 PM EDT

We have a large incense cedar (I think that is what it is) in our back yard. Pretty close to a year round creek. This year it looks really brown. I'm wondering if this is part of its natural life cycle, or if there is something I should do to aid its health? Since the weather has been hot and dry lately I've started giving it some water at the base of the trunk. It sits on a slope so that is the only place that seems to hold the moisture without running off.

Multnomah County Oregon forestry trees and shrubs urban forestry cedar

1 Response

Thanks for your question about your browning tree. This is a problem a lot of people are dealing with, and we get lots of questions like yours! I can't tell for sure from the photo if your tree is an incense cedar, but whichever kind it is, the level of browning is more than the natural loss of older growth would account for. If you can send close-up pictures of healthy foliage, showing both detail and the growth pattern, it will be possible to identify it for sure. Below are some possible causes of the browning, and questions for you to answer for a further diagnosis.

Environmental stress such as wind, flooding or drought (which has been occurring with more regularity in recent years as the climate warms) weakens trees to such an extent that they can no longer fight off insect infestations. Other stressors include cutting the trunk with a lawn mower or running into it with a vehicle. Regularly over-watering or extensive flooding fills the air pockets in the surrounding soil, robbing the tree of oxygen. Incense cedars (Calocedrus decurrens) weakened in any of these ways become susceptible to insect damage from flat headed woodborers (Buprestids) and cedar bark beetles (Phleosinus spp.). Do you see signs of insect damage such as sawdust or borer holes in the trunk?

Tree damage is usually due to a combination of factors. Multiple actions or changes may be needed to relieve stress and increase tree vigor. Possible strategies include:

  • Prevent soil compaction caused by vehicle or animal traffic near trees. Compaction can damage surface soils and roots, especially in clay soils.
  • Avoid direct damage to trees and roots by animals or machinery.
  • Reduce competing vegetation.
  • Irrigate landscape trees during dry spells. Apply water slowly over many hours, avoid frequent shallow watering. Apply mulch to maintain soil moisture.
  • Do not alter drainage near established trees (ditches, ponds, fill or removal of soil)
  • If insects or branch/stem cankers are evident, prune and destroy affected branches to reduce spread.
  • Do not fertilize during drought conditions; fertilization can increase a tree’s water requirements.

Here is are a couple of publications that you may find useful:

http://blogs.oregonstate.edu/treetopics/2014/06/27/whats-causing-die-back-incense-cedar/

https://www.oregon.gov/ODF/Documents/ForestBenefits/TreeDeclinesRedcedar.pdf