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
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.
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 840,
Crop Protection Guide 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.