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Euonymous Scale, Unaspis euonymi (Comstock),
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| Author: | Christoph Kessel - Nutrition Horticulture Program Lead/OMAFRA |
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| Creation Date: | February 1998 |
| Last Reviewed: | July 2003 |
Euonymus scale has become a concern in many landscapes. Scales are insects. Generally, they can be described as small bumps which can be easily scraped away. They are often found on trunks, twigs and branches. Scales have three stages of development: egg, nymph or crawler stage, and adult stage. As a nymph, the scale is mobile, crawling around looking for new places to feed. When mature, it produces a protective covering over its body. The adult scale is immobile. Scales can be divided in to two groups:
Euonymus scale is a hard or armoured scale.
Scales injure plants by sucking on plant juices. High populations of scales reduce plant vigour, cause leaf drop and eventual plant death.
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Euonymus spp., especially
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Examine leaves in June and July for feeding or sucking injury. It appears as small yellowish or whitish spots along the main vein of the leaf. Look at the underside of the leaf to see scales. Twigs may be covered with small, greyish-white bumps which can be easily scraped off with the thumb nail. Leaf drop and plant death can occur. Plants near buildings tend to be more prone to attack. These are areas of poor air circulation, high temperatures, and low soil moisture.
The greyish adult female scale, about 2 mm long, looks like an oyster shell. The male is smaller, narrower and white. It is the male that gives the branches its white appearance when populations are high. The nymph or crawler is orange - yellow in colour.
Euonymus scales overwinter as mature, fertilized females. In the early spring, eggs are laid underneath the protective scale. Eggs hatch late May to early June over a period of 2 - 3 weeks. Crawlers migrate to the leaves to feed. They may also be blown by the wind to other susceptible host plants. There can be a second generation in mid July.
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Where possible prune out and destroy infested branches or plants before crawlers emerge.
When planning a chemical control program for scales, remember that insecticides will not penetrate the shell or protective scale once it has formed. Strategies must be aimed at the overwintering adult and the crawler.
Dormant oils will provide good control for the overwintering female scales. In order to be effective, the oils should be applied in a large volume of water. Stems must be thoroughly covered in order to suffocate the overwintering adults. Using oils may burn leaves on broad-leaved euonymus selections.
Crawlers hatch over two to three weeks. To monitor for crawlers, wrap black electrical tape, with the sticky surface facing out, around the twig. The tape should be placed on the twig above the overwintering females. Crawlers will stick to the tape as they migrate to feeding sites. Begin looking and treating for crawlers about the time Syringa reticulata, Japanese tree lilac and Catalpa speciosa, northern catalpa are in early bloom. Monitor for a second generation around mid-July. Contact or systemic insecticides will provide the best control. Four sprays, applied 10 to 12 days apart as the crawlers begin to emerge, may be necessary.
For recommended chemical controls order OMAFRA Publication 383, Production Recommendations for Nursery and Landscape Plants.
Always read the Label!
Euonymus kiantschovicus, spreading euonymus, is reported to be resistant to euonymus scale. However, its hardiness is restricted to the shores of the Lakes Ontario and Erie. It can experience winter burn and generally has an untidy appearance.
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