Symptoms

• Rot diseases in Douglas firs can be mis-diagnosed as other diseases.Jupiterimages/Photos.com/Getty Images
  
  Though caused by dozens of differing fungal pathogens, symptoms of Douglas fir suffering from rot diseases present similarly. The entire tree is affected as opposed to individual branches. Affected trees may appear as though suffering from drought stress. A change in color is usually the first noticed symptom. Needles will usually turn yellow, but can turn shades of purple to rust colored. Defoliation of the needles and eventual total decline of the tree will ensue shortly thereafter.
  
  

Disease Characteristics

• Saplings succumb to rot diseases faster than mature trees.Comstock Images/Comstock/Getty Images
  
  The fungal pathogens that cause rot diseases in Douglas fir trees can survive in soils for many years if the soils are moist and no other host is present. In the absence of moisture these diseases do not survive for more than a few months. Immature Douglas fir trees are more susceptible to rot as their root systems are smaller and weaker. With some types of rot pathogens, mature Douglas fir are able to partition the disease and may survive for some time or may potentially recover if the disease is not severe and if conditions change.
  
  

Other Considerations

• Careless watering can aid in the spread of diseases.Comstock Images/Comstock/Getty Images
  
  Fungal diseases can infect all types of trees. In areas where other trees have died and the stump still remains, rot diseases can remain active for many years in those decomposing stumps. Douglas fir trees should not be planted in areas where there may be rotting stumps of previously infected trees.
  
  Fungal pathogens can also be spread by splashing water. Care should be taken when irrigating Douglas fir so that water seeps into the root zone as opposed to splashing on the foliage.
  
  

Prevention

• Douglas firs should not be planted in clay soils as they are slow to drain.Photos.com/Photos.com/Getty Images
  
  The most effective way of combating potential rot diseases on Douglas fir trees is to make sure that they are properly sited. Douglas firs require a soil that drains quickly as their roots are intolerant of excess moisture. Make sure that good air circulation exists around your Douglas fir to expedite the evaporation of the soil moisture. Remove any weeds that may be growing underneath the trees and clear any brush or unwanted plants that may be blocking good air flow around the base of the trees.