Question of the Week #1: September 1, 2016
“Neil, what is wrong with my euonymus plants? Is this some kind of insect, or is it a fungus? What can I use to kill it? Can the plants be saved?”
Green euonymus is being assaulted by a new outbreak of scale. If controls are not implemented at once, it will kill the shrub. (Dead scales remain attached to the plant, but they are dry and flakey when rubbed. Living scales will exude a yellow liquid when crushed.)
This is euonymus scale. It’s a very slow-moving (crawler stage) or fixed insect (adult stage) that attaches to the plants’ leaves and stems and sucks the very life out of them.
If you have euonymus shrubs, it’s not a matter of “if” they will develop scales, but “when.” They will get euonymus scale, and odds are extremely high that it will kill them. That’s why you’ll rarely see landscape designers call for shrub forms of euonymus. The risks are huge, and the rewards are short-lasting.
If you are vigilant about watching for scale, you may be able to help your plants survive by applying a systemic insecticide in mid-spring, also by applying a horticultural (“dormant”) oil in January. But if you ever let down your guard, scale will find your plants and probably consume them.
Many first-time gardeners are smitten by the glossy, variegated leaves of golden euonymus. However, it is a ticking time bomb in the landscape. It’s best to avoid it, or if you already have it, replace it should it develop an outbreak of scale.
Once scale gets to the point you see in the photo of golden euonymus, there’s no stopping the freight train. It’s time to replace them with some other, more dependable shrub. Don’t feel like you have to find a variegated shrub, either. Solid green plants are just fine. You can add color with annuals and perennials.