Scouting and Control of Common Pests of Fraser Fir  

Phytophthora Root Rot (PRR)

Phytophthora root rot (PRR) is the only serious disease of Fraser fir Christmas trees in western North Carolina. It is caused by a soil-borne fungus, Phytophthora cinnamomi, which infects tree roots. Fungal spores are produced in response to water in the soil. Soils only need to be saturated for several hours for Phytophthora to infect roots if the fungus is present. Phytophthora root rot is controlled by only planting Fraser fir in fields where water drains quickly both off the field and down through the soil, and by planting disease-free seedlings.
    Symptoms. The above-ground symptoms of PRR on Fraser fir include yellow-green needles, wilting, dead branches, and tree death. The needles usually remain on dead branches and turn cinnamon brown. Roots of affected trees are cinnamon-red turning black and lacking white growing tips. The outer surface of the root can be pulled away from the inner core. Feeder roots are absent. Cutting into the bark of the trunk of the tree may reveal butterscotch-colored wood. Many of these symptoms may initially be present on only one side of the tree or on lower branches, since the fungus first infects a root and grows upward into the trunk on that side. Eventually, the entire tree will die. Infected trees are usually found grouped together in a field or bed. Unfortunately, a tree may be infected with the fungus months to years before the above-ground symptoms are seen.
    Similar appearing problems. Dead and dying Frasers can have many causes. To positively confirm a diagnosis of PRR, it is necessary to send root samples to the Plant Disease and Insect Clinic in Raleigh. Contact your county extension agent to send in samples.
 

 
 
    When to scout. Assess field sites for potential Phytophthora problems before Fraser fir is set. After trees are planted, assess the cause of dead or dying trees to determine if PRR is the cause.
    Scouting method. To assess a potential field site for problems with Phytophthora, evaluate the surface, subsoil, and water drainage in the field. Information on soil type and characteristics is available from soil survey maps. However, it is also important to assess soil characteristics in person at the site.
    Water drainage is one of the most important factors contributing to PRR. It may be necessary to go to a site during a heavy rain to observe water drainage. Most growers know not to plant Fraser fir in a low lying, wet area. Wt weather springs, or a culvert or road draining into a field can also cause problems. Be sure you are not creating water drainage problems when placing field roads.
    The soil texture and structure in both the surface of the soil and the subsoil will determine how easily water will drain through the soil profile. A high clay content decreases water flow and holds water longer. Clay in the topsoil is a potential problem, as is clay in the subsoil, even a foot below the topsoil.
    Hardpans and shallow soils will slow water flow. Rock outcropping close to the soil surface may retain water. Compacted soils also hold more water and slow water flow down through the soil. Compacted soils will also increase surface runoff that can quickly spread this disease.
    To determine if a dead or dying plant has Phytophthora, pull up the affected trees and examine the root system for blackened roots. The surface of the roots will pull away from the core. Unlike root damage from white grubs, trees infected with PRR will still have feeder roots. The trunk wood of infected trees may be discolored.
    Control. Controlling PRR requires an integrated pest management approach. No single control strategy will prevent or control this disease. As with most plant diseases, the best control is avoidance. Plant only healthy transplants on appropriate sites. If trees become infected with Phytophthora, try to reduce the spread of the disease and minimize financial loss with management practices like maintaining ground covers, quarantining affected areas, and quickly harvesting trees to avoid further losses.