douglas fir treatment

Asked February 21, 2018, 2:32 PM EST

our development has a fairly large d. fir that is thinning out and producing a large amount of cones. Concerned it may be slowly dying. Looking for suggestions how we might treat/save the tree

New Castle County Delaware

1 Response


Douglas fir is a popular Christmas tree in our area, but can sometimes be difficult to keep in the landscape. Excess production of cones is a sign of stress. They are susceptible to several fungal needlecast diseases. In the past ten years, Rhabdocline needlecast was the primary problem, but in the past two or three years, Swiss needlecast has been very problematic. The fungus produces spores on the second year (two year old) needles in the spring and the spores infect the developing new needles as they expand. The control and management includes the application of the fungicide chlorothalonil to protect the new needles. Timing is very important, with applications in early May, and then two more applications 10 days and 20 days after the first. Coverage to the tree is also important, and may be difficult for a homeowner to do. You may want to call a tree company, a certified arborist to treat your tree. It will take two years to get the disease under control. Old affected needles will gradually fall off, but will not improve, in other words the fungicide doesn't cure the disease, it merely protects the new growth.

Thank you for contacting Cooperative Extension,