Spruce trees are popular options for many homes and businesses, providing an elegant look as well as shade, privacy and decoration. Like any tree, though, spruce trees can be affected by some arthropods and pathogens. Spider mites and needle cast are two of the most problems that may be seen in spruce trees. Let’s look at these issues and what you can do to prevent them.
Damage from spruce spider mites most often becomes noticeable during the summer months when trees are stressed by the dry, hot weather. The actual damage typically occurred as the mites were feeding during cooler weather, but only becomes obvious in the warmer months.
Spruce spider mites can be seen with a magnifying lens, and appear as tiny white or yellow specks on the needles. As with other types of spider mites, a common test for spruce spider mites is to tap a branch while holding a white piece of paper beneath it and looking for the mites to fall on the sheet, where they will be obvious as tiny specks on the paper. More than 10 mites per sample generally indicates that some kind of pest intervention may be needed, notes a recent article in The Pierce County Tribune.
There are several approaches for treating spruce spider mites. These include chemical controls, biological controls, cultural control and syringing (spraying mites with a blast of water).
Needle cast diseases occur as a result of a fungal infection. Trees located in wet, humid environments are more susceptible to this type of fungal infection than trees in drier environments.
The symptoms of needle cast include discolored needles that may turn a brown or purple color before dying entirely, though fresh needles from the current year will not show symptoms. The fruiting bodies of the attacking fungi are microscopic, but can be seen along the stomata of the needle with a 10x magnifier. The fungi will appear as rows of small black dots along the underside of the needles.
Needle cast can be treated with fungicides. Treatment is done with a fungicide that contains chlorothalonil, says The Tribune, and will need to repeated for two or three years to achieve effective control. Affected trees should recover within a few years with proper treatment, provided the problem has not been left untreated for too long.
It is a good idea to consult an arborist or county extension agent if there are any questions about whether it is an arthropod or pathogen that is causing problems with spruce trees as the treatment regimens differ significantly.
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