Spruce Tree Needle Drop
Is your spruce tree losing needles everywhere? Don’t worry too much many causes of needle drop can be treated by your certified arborist.
Spruce trees naturally shed needles – this is part of a healthy needle lifecycle of 5-7 years. In the forest, dropped needles act as a self preservation mechanism. The discarded needles acidify nearby soil, reducing nutrient and light competition from less acid tolerant species.
However, in Calgary, spruces often experience an unnatural amount of needle drop. There are many causes of this from fungus infestation to road salts to compacted clay soils. Even late winter freeze-thaw cycles can damage needles.
About 80% of the needle cast we see in Calgary is due to the following issues:
1) Cytospora Canker
This is a fungal infection characterized by random dead branches, and a smoky-white coating on the trunk of the tree coupled with oozing sap. This infection causes unsightly gaps in tree branches, copious needle shedding, and is often the final infestation that kills a spruce. It is most often found in Colorado blue spruce.
Cytospora canker can be treated with an antifungal trunk injection treament administered by your arborist.
2) Spider Mite
Common in dry climates, spider mites are detected by fine silky webbing in the spruce’s branches. They often cause inner branches to turn red and drop interior needles. Spider mites cause unsightly damage but are not usually fatal to the tree.
Spider mites can be treated with a miticide injection treatment in early summer.
3) Spruce Budworm
Unlike the two previous infections,these catepillars feed on new growth. Budworm defoliates new shoots and makes a tree look red or orange tipped. A heavy infestation of budworm is fatal after 2-3 years.
Spruce budworm can be treated with a trunk injection administered in spring or early summer.
4) Spruce Needle Rust
Fungal infection that causes inner needles to turn pinky-brown throughout the tree. These needles will often fall off the following year. New growth appears unaffected. Needle rust is unsightly but not fatal.
Spruce needle rust often takes over after a tree has been treated for Cytospora Canker and/or an insect or mite infestation. When we plan a pest treament program for a spruce, we recommend a small follow-up treament for needle rust several months after a tree is treated for other pests.
5) Rhizosphaera Needle Cast
Another fungal infection that mostly affects blue spruce. It causes two year old and older growth to turn purple. The needles then die and fall off the following year. Unlike the spider mite, damp, humid conditions encourage the growth of this pest.
Rhizosphaera needle cast can be treated with a trunk injection. However, it is particularly stubborn and usually requires two consecutive annual treatments. These treatments are most effective when the tree is experiencing humid conditions in the spring and early summer.
In summary, these are the most common reasons for spruces losing needles but are by no means the only causes. Often, a tree that is weakened by dry conditions, alternate freeze thaw cycles, or branch damage hosts multiple pests. It is recommended to contact your certified arborist (with experience in pest control) for a complete diagnosis and tree pest management plan.