Rhabdocline needlecast is an important disease to know and control if you grow Douglas fir or have properties with Douglas fir. Only Douglas fir is susceptible to this needlecast. Badly infected trees will lose a considerable number of one and two year old needles, which renders the plants unsaleable come Nov. and Dec. in nurseries and Christmas tree plantings. The plant tissue covering the spore bearing structures is just splitting and the buds are emerging in this area, so the timing is right for a treatment in the next few days. Now would be a good time to scout plantings for symptoms and treat if the disease is seen. Bravo Weather Stik or other labeled formulation of Bravo or Daconil (chlorothalonil) is the least expensive and effective if applied at the proper time.
Cultural Control
>Control vegetation around base of trees to increase air circulation and reduce moisture conditions necessary for infection.
>Plant healthy stock.
>Identify disease early to minimize losses.
>Shear trees in healthy plantations first to avoid contamination of these plantations by workers' clothing and equipment.
>Sterilize tools by dipping in denatured alcohol for 3 minutes after shearing infected plantations.
Chemical Control
Trees should be sprayed with chlorothalonil (Bravo or Daconil 2787). Foliage should be completely covered. Three fungicide applications are generally recommended. The first should be made when at least 50% of the buds have broken and the new growth is 1/2 inch long. Make two more applications at two to three week intervals after the first.
Information from Bob Mulrooney, Extension Plant Pathologist, UD.
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