Forestry Branch
Spruce Bud Scale in Manitoba
In Manitoba the spruce bud scale, Physokermes picea, attacks Colorado, white and black spruce. In recent years this insect has become a chronic problem of ornamental and shelterbelt spruce trees.
The female adult scales are round and reddish-brown in colour. They are approximately 3 mm in diameter. They are stationary, often located in clusters of three to eight at the base of twigs. The female adult scales very closely resemble spruce buds and consequently, often go unnoticed. Lower branches on the tree are often the most heavily infested.
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Eggs are formed under the adult female scale. Following hatching the young nymphs or crawlers migrate to the needles, insert their feeding tubes and suck the juices from the needles. Crawlers actively feed through late June to early August. They over-winter in an immature form on the under side of the needles or clustered around terminal and lateral buds. In the spring the females move onto the twigs to complete their development. There is one generation per year.
Heavy feeding causes discolouration and loss of needles. The crawlers excrete a sticky sweet liquid called honeydew upon which black sooty mold grows, covering both the foliage and branches. Heavy scale infestations kill lower branches and reduce overall tree vigor, which increases susceptibility to damage from other insects and disease.
If excessive needle loss and sooty mould is noticed on branches, inspect them closely for the adult female scales. If warranted, trees may be sprayed with a registered insecticide such as malathion, dimethoate or diazinon while the crawlers are active.
