Douglas-Fir Needlecast Management

Abstract

Douglas-firs have recently fallen out of favor due to widespread and persistent problems with needlecast diseases which lead to needle discoloration and sparse foliage. Whether in the landscape, nursery or at Christmas tree farms, trees not treated with fungicides will suffer to varying degrees. Two important principles seem to be emerging from the three years of the research study looking for ways to optimize the fungicide applications and reduce the numbers of treatments necessary: 1) Spraying before the buds are fully opened and shoots are elongated to at least an inch is not effective. 2) After the shoots are at least an inch long, there seems to be at least a three week window to make an application. Although the timing may not be critical thorough coverage is important to protect whatever needles are there.