I have Euonymus ‘Sarcoxie’ growing on a chain link fence. Every year, the plant is covered with small bumps and many of the leaves yellow. I think it is scale. I trim out the infested stems, but it seems to come back worse every year. Is there a way to get rid of it without using insecticides or am I fighting an uphill battle? I have a healthy Euonymus ‘Emerald ‘n’ Gold’ nearby. I wonder if I should remove the ‘Sarcoxie’ before it might infect the healthy plant?
The symptoms you describe are the calling card of Unaspis euonymi or euonymus scale. As they feed, these tiny insects cover themselves with nearly microscopic shells that range in shape and color. These well-armored pests are feeding on the undersides of the leaves, causing the yellowish blotches. You are correct to prune out badly infested growth. The gnarly growth habit of euonymus does not easily lend itself to being scrubbed with a soft brush and soapy water, a treatment that works for some scale infestations. Application of dormant oil before plant growth starts in spring may turn the tide, followed up by a summer oil treatment in late June or July when the crawlers emerge (baby scale insects). These oils are not what you really think of as insecticides, the oils merely smother the offending critters. To know when to apply the summer oil use the black electric tape trick. Wrap some black electric tape, sticky side facing outward, around a branch of the plant where you can see scales. When the crawlers hatch they will climb around and stick to the tape looking like whitish dust. Treat with summer oil immediately. Dormant oil and summer oils are different formulations, and used at the wrong time can damage the plants, so read the labels and make an educated choice of products. However, scale in euonymus can be lethal. Because popular varieties of euonymus are readily available at nurseries, you might save yourself a great deal of trouble by removing the ‘Sarcoxie’ before the scale can infect your ‘Emerald ‘n’ Gold.’ Scale, once established, is difficult to eradicate by even the most vigilant gardener. You may prefer to avoid the uphill battle and start fresh!