The Alaskan Weeping Cedar (Callitropsis nootkatensis ‘Pendula’) is a distinctive conifer prized for its graceful, drooping branchlets and slender, pyramidal form. Native to the cool, moist Pacific Northwest, this cultivar is a popular ornamental tree. Because of its specific habitat requirements, it is susceptible to various issues when planted in less-than-ideal conditions. Understanding these common stressors, pests, and diseases is important for maintaining the tree’s health.
Environmental and Cultural Stressors
The most frequent problems stem from improper site selection and planting practices. A primary concern is soil drainage, as this conifer naturally prefers moist, yet well-drained, soil conditions. When planted in heavy clay soils or areas where water pools, the tree is susceptible to “wet feet,” which quickly leads to root stress and decline. This environmental stress often predisposes the tree to secondary infections.
The Alaskan Weeping Cedar thrives best in cooler climates. Excessive heat or intense, full afternoon sun can cause significant damage, especially outside of its native range. In warmer zones, the tree benefits from partial shade, as direct, scorching sun can lead to needle burn. This foliage scorch is exacerbated when the tree is subjected to drought or wind stress.
Improper planting depth is another common cultural error. Planting the root ball too deep or allowing mulch to pile up against the trunk (“volcano mulching”) can suffocate the root collar. This practice restricts the exchange of oxygen and carbon dioxide, leading to root suffocation and decline. Large, mature specimens can also struggle with transplant shock, making careful site selection important.
Pest Infestations
Several arthropods target the Alaskan Weeping Cedar, causing stress and diminishing its visual appeal through sap-sucking. One common issue involves spider mites, tiny arachnids that feed on the needles. Their feeding removes chlorophyll, resulting in fine stippling on the foliage that may turn bronze or rust.
Spider mites thrive in hot, dry conditions, making water-stressed trees vulnerable to rapid population growth. Severe infestations may produce fine silken webbing between branches. Another sap-sucking threat is scale insects, which appear as small, armored bumps attached to the branches and needles.
Scale insects extract sap, causing faded color and twig dieback. They excrete sticky honeydew, which attracts other insects and serves as a medium for black sooty mold growth on the foliage. Aphids are occasional pests that target tender new growth, also contributing to honeydew production and shoot discoloration.
Disease Pathogens
Disease pathogens, particularly those affecting the root system, pose a threat to the Alaskan Weeping Cedar. The most serious disease is root rot, caused by the genus Phytophthora. This soil-borne water mold thrives in saturated, poorly draining soil, where it infects and destroys the root system.
Symptoms of Phytophthora infection include general decline, sparse canopy, needle discoloration, and eventual death. Because damaged roots cannot transport water and nutrients efficiently, the tree exhibits symptoms often confused with drought stress. Another fungal concern is needle blight or tip dieback, often caused by fungi like Sirococcus or Phomopsis.
Needle blight typically begins with the browning or graying of needles, starting at the shoot tips and progressing inward. These pathogens can create cankerous lesions on infected stems. Cankers are sunken, discolored areas on branches or the trunk, and can also be caused by fungi such as Seiridium entering through wounds or stress points.
Preventative Care and Treatment
Mitigating problems begins with selecting an appropriate planting location. The site must offer well-draining soil to prevent saturated conditions that favor root rot pathogens. In warmer climates, choosing a location that provides relief from intense afternoon sun helps prevent scorch and reduces heat stress.
Proper cultural practices are effective preventative measures. These include correct planting depth, ensuring the root collar is visible, and using mulch in a shallow ring away from the trunk. Correct watering involves providing adequate moisture but allowing the soil to dry slightly between waterings for root aeration. Pruning should remove dead, diseased, or discolored material during dry weather to prevent fungal spread.
For managing pest infestations, horticultural oils or insecticidal soaps effectively control spider mites and scale insects by suffocating them. Careful application is necessary to ensure complete coverage. When addressing root diseases like Phytophthora, the primary action is improving soil drainage, as chemical treatments are often ineffective once the disease is advanced. Sanitation, including removing severely infected trees, prevents the pathogen from spreading.