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. 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. This tree typically reaches heights of 50-70 feet with a trunk diameter of up to 2 feet. The white spruce is a widespread North American species that grows from Newfoundland and Labrador west to British Columbia and as far south as Minnesota and West Virginia. Please contact us if you have any questions. Image Credit: Eva Pruchova, Shutterstock. Continue applications through periods of wet weather. Plant attributes, such as required environmental conditions, and soil and water requirements are listed below. 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. In the snowy North, where landscapes can look barren in winter, evergreens such as Colorado blue spruce trees can provide much-needed winter interest.Authors: Brian Hudelson, UW-Madison Plant Pathology But they’re equally effective as specimen trees.Ĭolorado blue spruce trees are valuable in deer country, as their prickly texture and strong aroma render them conveniently deer-resistant. Plant in full sun to partial sun in a location with moist, fertile soil.Ĭan be planted in rows to form windbreaks. Sun and Soil Requirements for Colorado Blue Spruce Trees: Prune off half of the fresh growth on each candle (i.e., growing tip) in spring. Plant Care for Colorado Blue Spruce Trees:Ĭolorado blue spruce trees don’t need to be pruned, but they can be pruned if you wish to promote denser foliage. The pyramidal shape of Colorado blue spruce trees makes them a classic choice for Christmas. Their silvery-blue needles are prickly to the touch and aromatic. ![]() USDA Plant Hardiness Zones for Colorado Blue Spruce Trees:Ĭolorado blue spruce trees can be grown in zones 3-7.Ĭharacteristics of Colorado Blue Spruce Trees:Ĭolorado blue spruce trees typically reach a height of 30′-60′ and spread out 10′-20′.
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