|Have you ever seen boxwood leaves cupped and curled like this?
These leaves have curled because of a sap sucking insect called, psyllids. Boxwood pysllids (Psylla buxi) sort of resemble aphids as nymphs - with size and colour. There's usually one generation a year and control is best with an insecticidal soap application in late spring (May in Ontario). Treat when the new growth of leaves fully open. Psyllids don't kill boxwood, but will distort and affect the foliage - aesthetically ruining the glossy look to this broadleaf evergreen.
|In these photos, you can see remnants of their past presence. Their feeding has cupped the foliage right over the bud tips. Causing the tip of the stems to wither and dry up.
|You can also see remnants of their excrement - a white residue.
When psyllids nymphs are high in number, you may see their white, waxy excretion before the leaves curl. Usually at the tip of the branch stem. As they feed, the boxwood leaves respond by cupping - sheltering them, where you don't see the nymphs at all. Psyllids usually feed on young, new growth that is tender. Hence the reason the leaves curl so easily.
|Their white frass (poop) is quite fluffy and insulates them as they feed toward the bud union of the leaf.
|Psyllids have flat bodies, with large eyes. I wish my camera could take a better photo, but you get the idea on how small they are compared to my fingers.
Psyllids lay orange eggs between the bud scales. As the leaves emerge from the buds, the eggs mature and hatch into nymphs - then the feeding begins. Nymphs become a flying winged adults (which look like miniature cicadas) in June and reproduce, laying the eggs near the terminal buds for next years cycle.
I've found you can reduce psyllid numbers drastically with just water. A high pressure spray dislodges many of them and reduces the adult population. Just be aware, adults may be blown off and fly back. So the spray of water needs to be repeated and quite high in pressure.
Not a huge problem, but easily treated.
|Above are photos of other notable boxwood characteristics that have confused folks often. These are boxwood flowers (left) and last years seed husks. I've had folks ask me if the right photo is a disease. ;)