There are odd-looking white spots on a section of my pachysandra bed. I was wondering what they are and if I should take some action if they are a problem.
— Zachary Frederick, Kildeer
From your photo, it looks like your pachysandra has an infestation of euonymus scale. This is the first time I have seen this problem on pachysandra. This pest injures the host plant by using its piercing-sucking mouthparts to feed on plant sap. It is a difficult pest to control, as adults create a protective covering (armoring) that makes insecticides ineffective while they are covered. You should address this pest in your garden once populations get large.
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Right now, you don’t need to do anything. The female scale insects overwinter on the plants and begin laying eggs in late April and May. They hatch over a two- to three-week period into crawlers. The males feed under a narrow, white, waxy coating and mate with females in spring. The crawlers wander about the plants for a short period of time and then begin to feed and create a waxy covering. A second generation of crawlers is produced from late July through August. The best time to apply control for this insect is when they are in the crawler stage.
I suggest that you prune out all the infested areas of your pachysandra bed next March to remove the overwintering females. Discard the plant debris in the garbage or at a commercial landscape waste operation where compost piles will get hot enough to kill the insects. The crawlers are active from late May to early June and in late July through August, providing two windows of opportunity to apply a control measure. Removing the overwintering adults from your garden should reduce the pests significantly. Apply a summer-weight dormant oil to your pachysandra during the crawler stages for more control.
For more plant advice, contact the Plant Information Service at the Chicago Botanic Garden at [email protected]. Tim Johnson is senior director of horticulture at the Chicago Botanic Garden.