Treating sap-sucking scale in your garden
Gardening teaches you to be observant and to be patient. A case in point: One way to look at your garden is to admire your own handiwork. Admire the fruits of your own labour, so-to-speak. Another way of looking at your garden is: What is really going on in my little plot of land? What am I missing, meaning what insects and diseases may be lurking here, that I’m not paying attention to? Wise gardeners inspect their gardens weekly to see what is really going on.
On our weekend inspection, we found greedy scale had made itself right at home on an ‘Ivory Halo’ Dogwood, a shrub that is well established in our garden. ‘Greedy scale’ is not a value judgement, it is what this pesky insect is called. Scale is a family of sap-sucking insects that have the shape of a single clam shell; when a colony erupts in your garden, they look like fish scales, which is where the name comes from. There are more than 25 species of scale that are different sizes, colours, and find certain plants and shrubs particularly tasty.
Scale is an insect that thrives in sheltered places in your garden where there is poor air circulation. If your garden is over-planted, improve the air circulation around your shrubs by opening up the branches with pruning. And carefully check any plants and shrubs growing in the corners of your garden, especially if you have a wooden board fence that provides lots of wind protection to scale.
Here is a great website, from the University of California at Davis, that gives you everything you need to know about scale—and how to treat it. Spraying your plants and shrubs with horticultural oil in early spring is the best remedy, to preempt the growing cycle of scale. Scale is a crawling insect that over-winters in the ground and then heads upward along plant stems and shrub branches. All those wounds caused by thousands of sucking mouths of scale typically cause secondary infections, like black mold or powdery mildew.
The good news is that some plants and shrubs can survive an attack including: boxwood, chestnut, holly, ivy, elder, magnolia, mulberry, junipers, maple, privet, and willow.
There is a particular type of scale that attacks evergreen Euonymus japonicas; we lost two euonymus shrubs to scale during the past 10 years. The Royal Horticultural Society in the UK has a special website just for Euonymus scale.
If your shrub is badly infected, consider pulling it out altogether. Dispose of it in the garbage; do not compost it, passing on the problem to other shrubs in other gardens. And don’t re-plant the same shrub in the same spot because the risk of re-infection is great.