Rhizosphaera Needle Cast
Rhizosphaera Needle Cast
What is Rhizosphaera needle cast? Rhizosphaera needle cast is the most common disease of Colorado blue spruce in Wisconsin. It makes Colorado blue spruce unsightly and unusable in many landscape settings. The disease can also affect other conifers including black, Engelmann, Serbian, Sitka, and white (e.g., Black Hills) spruce.
What does look like? The first noticeable symptom of Rhizosphaera needle cast is browning and loss of the innermost needles on lower branches of spruce trees. Often, the youngest needles at the tips of branches remain healthy. Rows of small, black spheres form along the length of infected needles and are visible with a 10X hand lens. These black spheres are fruiting bodies (i.e., reproductive structures) of the fungus that causes the disease and are diagnostic.
Where does it 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. 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.
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. Treatments will not cure existing infections but can prevent additional infections. Apply treatments every three to four weeks starting as new needles emerge in the spring. Continue applications through periods of wet weather. For fungicide treatments to be effective, thoroughly cover all needles. This may be extremely difficult with large trees. Be sure to read and follow all label instructions of the fungicide(s) you select to ensure that you use the fungicide(s) in the safest and most effective manner possible/ Or call a professional Arborist who specializes in Plant Health Care, who can find the right PCH treatment for your trees.
How do I avoid problems in the future? The easiest way to prevent Rhizosphaera needle cast is to avoid planting Colorado blue spruce. If you plant blue spruce, consider using dwarf varieties and allow adequate spacing between trees so that branches will not overlap when trees are full size. Dwarf varieties and properly spaced larger spruce varieties will have better air penetration and needles will dry more quickly. Dry needles are less likely to be infected. Also, check existing spruce trees for the disease. Remove and destroy any diseased branches and needles by burning (where allowed), burying, or hot composting.
For more information on Rhizosphaera needle cast and what you can do to help your trees; contact Johnson Ops Tree Care a ISA Certified Arborist with the right PHC (Plant Health Care) treatment for your trees. Call us today! at 608 526-6297