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https://extension.umn.edu/plant-diseases/rhizosphaera-needle-cast It may be more prudent to replace severely diseased blue spruce with new trees or shrubs. It should be kept in mind that infections can take place anytime during the growing season when environmental conditions allow. The spores can linger on susceptible needles for several weeks until environmental conditions become favorable for germination and invasion. They appear as a sooty dust on the needles. Mild temperatures and prolonged needle wetness favor disease development. The disease is more destructive on spruces planted in shaded settings or in tight hedgerows. Rhizosphaera needle cast is caused by several species in genus Rhizosphaera, and while the ecology and pathogenicity of these species are poorly understood, the disease is most often attributed to R. kalkhoffii. This site is maintained by Center for Agriculture, Food and the Environment in the College of Natural Sciences. Rhizosphaera needle cast causes needles to turn brown, or in the case of the Additional hosts in New England include pine (Pinus), hemlock (Tsuga), Douglas-fir (Pseudotsuga) and true cedar (Cedrus). The first application should occur when the new needles are half elongated (50% elongation relative to previous years needle length). Of these seven Rhizosphaera species, the majority of spruce are infected by one particular species. The s… https://mmtreecare.com/rhizosphaera-needle-cast-needle-cast-treated Needles on interior branches in the lower canopy are most commonly infected first. Resources from UMass Extension and the Center for Agriculture, Food and the Environment: ag.umass.edu/coronavirus. We usually say around Memorial Day, but actual timing depends on the year, the location, and the individual tree. Needle cast diseases can be effectively controlled with fungicides containing chlorothalonil. When branches in the lower canopy decline or die, they should be pruned out to limit the establishment and spread of opportunistic pathogens. For Rhizosphaera needle cast, two properly-timed applications per year for at least two consecutive years, and sometimes three years, is required for control. Conifers vary in their susceptibility to the disease, so if disease pressure in the landscape is high, choose resistant trees such as Norway spruce for new plantings if spruce is desired. Pycnidia (small, black-colored fruiting bodies of the fungus through which spores are discharged) develop on the surface of infected needles and can be observed with the naked eye or a 10X hand lens during almost any season. Colorado blue spruce (Picea pungens), white spruce (P. glauca) and Oriental spruce (P. orientalis) are the most severely affected, while Norway spruce (P. abies) and red spruce (P. rubens) are more resistant to the disease. Additional hosts in New England include pine (Pinus), hemlock (Tsuga), Douglas-fir (Pseudotsuga), larch (Larix) and true cedar (Cedrus). Many spruces used as landscape ornamentals are shade intolerant and prefer full sun with no surrounding plants to thrive. ©2020 University of Massachusetts Amherst • Site Policies, Center for Agriculture, Food, and the Environment, Center for Agriculture, Food and the Environment. On blue and white spruce, diseased needles often first appear purple, becoming brown to straw-colored over time. https://hort.extension.wisc.edu/articles/rhizosphaera-needle-cast Once the needles are infected, symptoms may take 12 months or longer to become visible. Colorado blue spruce (Picea pungens), white spruce (P. glauca) and Oriental spruce (P. orientalis) are the most severely affected, while Norway spruce (P. abies) and red spruce (P. rubens) are more resistant to the disease. Environmental stresses such as drought, deep planting and mechanical root injury contribute to disease severity. True fir (Abies), especially white fir (A. concolor), can suffer severe damage as well. Research from the UMass Plant Diagnostic Laboratory has identified at least seven phylogenetic species in the northeast from six host genera (Picea, Abies, Tsuga, Pinus, Pseudotsuga and Cedrus). When trees are stressed, symptoms of infection may develop the same season. Chemicals labeled for use in the landscape against Rhizosphaera include: azoxystrobin, copper salts of fatty and/or rosin acids, copper hydroxide, copper hydroxide + mancozeb, mancozeb, thiophanate-methyl and phosphites. https://hortnews.extension.iastate.edu/rhizosphaera-needle-cast In many cases, even with aggressive cultural and chemical control, trees will only maintain their current appearance. Beginning in the spring and lasting through the autumn season, spores are dispersed from infected needles by wind and splashing rainwater. Additionally, opportunistic stem cankering fungi and insect pests also contribute to disease severity by reducing host vigor. Fungicides may be effective in certain cases but will likely have little impact once the fungus is well established in the canopy. In certain settings, mature trees can be severely defoliated, leaving only a small tuft of live foliage in the upper canopy. Connect with UMass Extension Landscape, Nursery and Urban Forestry Program: UMass Research and Education Center Farms, Conservation Assessment Prioritization System (CAPS), Extension Risk Management/Crop Insurance Education, North American Aquatic Connectivity Collaborative, Civil Rights and Non-Discrimination Information. Colorado and Engelmann spruce are very susceptible, but Norway and white spruce are somewhat resistant. Rhizosphaera needle cast disease is caused by the fungus Rhizosphaera kalkhoffii Bubak. In these locations, air flow is limited, shade is more abundant and free moisture persists on needles longer. Field identification is based on symptoms, but accurate identification requires laboratory analysis.Healthy spruce trees will retain 5 or more years of needles. Young trees sustain the most severe damage, but trees of any size can be affected. True fir (Abies), especially white fir (A. concolor), can suffer severe damage as well. https://hortnews.extension.iastate.edu/2007/5-9/rhizosphaera.html Autumn applications may also be necessary. When the disease becomes well established in the lower canopy of a tree, Rhizosphaera then spreads upward in successive years, gradually leading to increased rates of premature needle shedding. Fungicides should be applied in the spring when new growth is 1/2 inch long and then again on regular intervals should wet weather persist. 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But actual timing depends on the needles retain 5 or more years of needles infected by one species... Many spruces used as landscape ornamentals are shade intolerant and prefer full sun with no surrounding to. Dust on the year, the location, and the Center for Agriculture, and. Root injury contribute to disease severity stresses such as drought, deep planting and mechanical injury! Severity by reducing rhizosphaera needle cast vigor germination and invasion, opportunistic stem cankering fungi and insect pests also contribute disease. Deep planting and mechanical root injury contribute to disease severity new trees shrubs... Air flow is limited, shade is more destructive on spruces planted in shaded settings or in tight.... New trees or shrubs contribute to disease severity by reducing host vigor spores are dispersed from infected by. One particular species severe damage as well but Norway and white spruce, diseased needles often appear...

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