It causes premature needle defoliation, resulting in loss of timber yield and, in severe cases, tree death. It is caused by the fungus Dothistroma septosporum (D. Scientific name of causal agent – Dothistroma septosporumĭothistroma needle blight (DNB) is an economically important disease of conifer trees (trees with cones and needles), and particularly pines (trees in the Pinus genus). Remove and destroy any diseased branches and needles by burning (where allowed), burying or hot composting.įor more information on Rhizosphaera needle cast: See UW-Extension Bulletin A2640, “Colorado Blue Spruce and Other Conifers Disorder: Rhizosphaera Needle Cast” (available at ) or contact your county Extension agent.Reportable in trade – see ‘Report a sighting’ below Also check existing spruce trees for the disease. Dry needles are less likely to be infected. Dwarf varieties and properly spaced larger spruce varieties will have better air penetration and needles will dry more quickly. If you do plant blue spruce, consider using dwarf varieties and allow adequate spacing between trees so that branches will not overlap when trees are full size. How do I avoid problems with Rhizosphaera needle cast in the future? The easiest way to avoid Rhizosphaera needle cast is to avoid planting Colorado blue spruce. Be sure to read and follow all label instructions of the fungicide(s) that you select to ensure that you use the fungicide(s) in the safest and most effective manner possible. This may be extremely difficult with large trees. For fungicide treatments to be effective, thoroughly cover all needles. Continue applications through periods of wet weather. Apply treatments every three to four weeks starting as new needles emerge in the spring. Treatments will not cure existing infections, but can prevent additional infections. How do I save a tree or shrub with Rhizosphaera needle cast? Consider treating affected trees with fungicides containing copper as the active ingredient (e.g., Bordeaux mixture) or chlorothalonil. Infected needles, including those that are still attached to branches and those that have fallen to the ground, produce spores that can be blown or splashed to healthy needles. Where does Rhizosphaera needle cast come from? Rhizosphaera needle cast is typically caused by the fungus Rhizosphaera kalkhoffii, although other species of Rhizosphaera can be involved depending on the host. These black spheres are fruiting bodies (i.e., reproductive structures) of the fungus that causes the disease and are diagnostic. Rows of small, black spheres form along the length of infected needles and are visible with a 10X hand lens. Often, the youngest needles at the tips of branches remain healthy. What does Rhizosphaera needle cast look like? The first noticeable symptom of Rhizosphaera needle cast is a browning and loss of the innermost needles on lower branches of spruce trees. Browning of interior spruce needles caused by Rhizosphaera needle blight. The disease can also affect other conifers including black, Engelmann, Serbian, Sitka, and white (e.g., Black Hills) spruce Austrian, mugo and eastern white pine Douglas-fir, balsam fir and western hemlock. It makes Colorado blue spruce unsightly and unusable in many landscape settings. What is Rhizosphaera needle cast? Rhizosphaera needle cast is the most common disease of Colorado blue spruce in Wisconsin. Authors: Brian Hudelson, UW-Madison Plant Pathology
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