Weeping spruce varieties (Picea spp.) add visual interest to home landscapes with their long, drooping branches, evergreen needles and attractive silhouettes. Weeping spruce varieties include the weeping white spruce (Picea glauca "Pendula") and the brewers' weeping spruce (Picea breweriana), trees that grow well in U.S. Department of Agriculture plant hardiness zones 2 through 9 and 6 through 8, respectively. The weeping blue spruce (Picea pungens "Pendula") and the weeping Norway spruce (Picea pungens "Pendula") both prefer the cooler summer temperatures in USDA zones 3 through 7. Like other conifer species, weeping spruces occasionally contract blight diseases.
Shoot blights occasionally infect weeping spruce trees. Sirococcus shoot blight pathogens (Sirococcus conigenus) attack new branch growth, initially causing the shoots to develop small purple sores. Needles attached to the infected shoot yellow before turning red-brown, dying and falling from the tree. Infections that spread into stems cause cankers to develop on the wood tissue.
Botrytis blight, also known as gray mold, is caused by fungal pathogens (Botrytis cinerea) that affect shoots and twigs, causing discolored, wilted and decaying plant tissue. Infected twigs often suffer from dieback, while the needles beyond the infection site wilt and drop from the tree. Grayish-brown spore masses frequently form on infected tissue when the humidity levels run high.
Minor needle blight infections sometimes affect spruce foliage, with Lirula needle blight being one of the most common. The fungal pathogens (Lirula macrospora) need several years to complete their life cycles. Early signs of Lirula needle blight include the foliage turning yellow or brown. As the disease progresses, the infected foliage develops raised black lines on the lower surfaces. Those black lines are actually fungal masses that release spores during wet weather. Once the fungal masses produce spores, the infected foliage turns gray-brown in color but stays attached to the spruce tree.
Diploda tip blight (Sphaeropsis sapinea) occasionally infects stressed or injured spruce trees. Early signs of tip blight include brown needles appearing on the tips of new branch growth. The infected foliage stops growing and looks stunted and sickly next to healthy needles. Infected twigs may also experience stunted growth as well as ooze a sticky substance that traps the blighted foliage on the tree. If you examine the base of the infected needles, you may spot tiny black fungal spores. Tree growth can be stunted if the Diploda blight infection damages the tree's terminal buds. The spores release during wet weather and spread via water droplets, wind or pruning tools.
Prune off infected plant tissue and immediately place the debris in plastic bags to limit fungal spore dispersal. Because the spores spread easily in splashing water, only prune diseased trees during dry weather. Sanitize your pruning tools between each cut by rubbing the blades with a 70 percent rubbing alcohol solution.
No chemical treatments exist for Botrytis blight, as of June 2013, but severe cases of other spruce blights often respond well to broad spectrum chlorothalonil-based fungicidal sprays. Following the instructions printed on the product's label, mix about 2-1/4 teaspoons of fungicide for each gallon of water. Spray the spruce thoroughly and repeat applications every seven to 14 days until the weather conditions in your area no longer promote fungal growth.
- Iowa State University Extension and Outreach: Sirococcus Shoot Blight of Spruce
- University of California Statewide Integrated Pest Management Program: Botrytis Blight
- Bonide: Fung-Onil Multi-Purpose Fungicide
- Cal Poly Urban Forest Ecosystems Institute: Brewer's Weeping Spruce
- North Carolina State University Cooperative Extension: Minor Pests of Fraser Fir Christmas Trees
- Washington State University Clark County Extension PNW Plants: Weeping White Spruce
- Cornell University Department of Plant Pathology and Plant-Microbe Biology: Diplodia Tip Blight
- Missouri Botanical Garden: Picea Pungens "Pendula"
- Missouri Botanical Garden: Picea Abies "Pendula"
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