Needle Cast or Needle Blight?
Over the past year our advisors have noted some interesting needle disorders in pine forests often resulting in spectacular colour changes that can be very concerning to forest owners and managers. Although this can sometimes be attributed to long established pathogens Dothistroma and Cyclaneusma, increasingly Physiological Needle Blight (PNB) has been the culprit. Outlined in this fact file is a summary of these three disorders based on many years of field observations by our advisors.
Physiological Needle Blight (PNB) is a very new disorder to many forest managers. Generally it affects trees older than 15 years, but will also be found in younger stands where it is often mistaken for Dothistroma and needlessly sprayed. The colour change can be rapid and spectacular with the red to brown-grey foliage becoming apparent as early as autumn, but peaking in the mid to late winter/early spring. Although there is some debate regarding repeated defoliation there is little doubt PNB and other disorders are a constant companion of some stands resulting in poor overall needle retention.
Dothistroma is a well-known needle blight more prevalent in the younger classes with trees building an increased resistance to severe infection from about 15 years in age. The assessment and treatment options for Dothistroma are well documented, but generally if the trees in a stand have around 15% of their green crown infected at the time of assessment in June-August, some level of spraying with copper fungicide should occur in the early summer.
Cyclaneusma is a very common fungal needle cast mostly seen in Spring and Autumn causing yellowing and sometimes red foliage to trees older than 12 yrs, however severe a-typical expression of this disease has been noted on much younger trees at other times of the year. The most recent year’s foliage is not affected as infection occurs a year before symptoms become apparent. No treatment is economically viable.
These common needle disorders are easily confused in the field. For further information, particularly with regard to disorder verification before spraying for Dothistroma please contact your Target Pest Forest Health Advisor.
PNB Developing on a 13 year old tree
PNB symptoms look similar to Dothistroma
Severe PNB on 19 year old stand