Euonymus scale

Asked July 5, 2016, 12:23 PM EDT

We have Euonymus growing along our chain link fence. A couple summers ago, we lost several due to Euonymus scale.

The Euonymus scale is back, with some of the plants having lots of the white scale along the "trunk" of the plant closest to the ground along with lower leaves -- some have so much that the branches come up from the ground are almost completely white. The Euonymus that seem to have it the worst are along the portion of the fence with the most shade (same as a couple summers ago).

Is there anything we can do to stop the scale and save the plants?

The plants looks similar to this:

Kent County Michigan trees and shrubs insect issues

1 Response

We do not recommend using contact insecticides to control scale unless absolutely necessary. Adult scales are relatively protected from contact insecticides by their waxy covering, but their immature forms, called crawlers, are susceptible. However, contact insecticides will also kill the naturally occurring enemies of scale. You can monitor the crawler emergence with sticky cards, double-faced tape wrapped around a branch, or by putting an infested shoot or leaf into a baggie and watching for crawler movement. Crawler activity often coincides with the flush of new plant growth in the spring. It's too late this year to target the spring hatch; however, a second generations will emerge around Mid-August.

Contact insecticides are harmful to birds, fish, pollinating insects and animals. If you choose this route, make sure that crawlers are present before using these pesticides (See above for timing the hatch.). Apply three sprays at 10-day intervals. As with all pesticides, read and follow all label instructions and precautions.

Horticultural oils (also called supreme, superior or summer oils) work very well to control armored scales, such as the euonymus scale, on ornamentals by penetrating their waxy covers and smothering them. Horticultural oil sprays will kill the eggs, crawlers (immatures) and the adult scales. Horticultural oils applied at higher rates of 3% to 4% (7-1/2 to 10 tablespoons oil per gallon water) during the dormant season (winter to early spring) will penetrate the thick waxy covers and kill the overwintering adults and eggs. Applications at lower rates of 2% (5 tablespoons oil per gallon water) can be used during the late spring (April) to target the crawlers and the newly settled scales with thin waxy covers. It is best to spray when temperatures are between 45 and 85 degrees and in the early evening due to plant sensitivity. More than one application may be needed.

Having said all that, you need to understand that euonymus scale is extremely difficult to control. Typically every leaf as well as the branches are covered with adult armored scales. A better approach might be to remove the infested shrub.

The following Euonymus species are resistant to euonymus scale: E. alatus ‘Compactus’ and E. fortunei Acutus.’ Consider using these in new plantings. With light infestations, scale can be scraped off by hand and destroyed. Prune out and promptly dispose of heavily infested branches. Scales tend to thrive on stressed plants. Follow a recommended fertility program and water plants weekly during drought to promote plant health.