Juniper Scale of Juniper

Disease Information

Juniper Scale

 Symptoms and damage

Symptoms of juniper scale (Carulaspisjuniperi) infestation are very similar to symptoms of spruce spider mite infestation. Initially, the juniper appears off-color and infested branches show little growth. The needles eventually turn yellow or brown. Branches may die back. If ignored, juniper scale infestation may kill the plant in two to three growing seasons. Signs of the pest include clusters of tiny bumps or scales about 1/8-inch in diameter, especially on the undersides of needles. Adult females are white at first but turn gray or black later. Adult females are mostly flat with a slight volcano appearance, if viewed through a magnifying lens. In addition, a shiny, sticky material (honeydew) is often seen on needles of junipers infested with juniper scale..Adult females survive the winter on the plant. In early spring, they lay eggs under their shell. The immature forms, called crawlers, hatch and crawl around before settling on the needles to feed. They feed by sucking plant sap. As they mature, they form a crusty shell over their bodies. Their legs become useless and they remain in one location. As they feed, excess sap is excreted as a sugary material, called honeydew. The sooty mold fungus can grow on the honeydew, forming dark splotches on needles.


 The presence of adults or crawlers determines which treatment will be most effective. Use a 2 or 3% horticultural oil mix as a dormant spray in late winter or very early spring before new growth occurs to control adult females by suffocation. A 2% solution is made with 5 tablespoons of horticultural oil per gallon of water. See Table 1 for examples of products. Most insecticides are effective only against the crawlers. Monitor the crawler emergence with sticky cards, double-faced tape wrapped around a branch, or by putting an infested shoot into a baggie and watching for crawler movement. Crawler activity often coincides with the flush of new plant growth in the spring. However, some scale species may have overlapping generations with an extended crawler emergence period, such as along the coast. Insecticides recommended for use against crawlers include acephate, malathion, cyfluthrin, and carbaryl. 

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