Depending on the weather conditions and plant growth in the garden we have a first preventive spraying round in mid-April. This year we had an early and fabulous spring with summer-like temperatures and little, actually far too less, rainfall. Due to this I started spraying with insecticide already in early April.
In Nasty insects in buxus (box) I wrote about insects in boxwood. One of the major pests, not as such in buxus but in our the garden as a whole, is the Boxwood psyllid or Cacopsylla buxi (Dutch: topmijt of buxustopmijt en buxusbladvlo).
This pest is the most serious pest of this evergreen plant and due to the harm it can bring, the most dangerous one in our garden.
Although I started spraying very early in the season with this systematic internal agent that gets into the sap-stream and is active for some three months, some weeks after the first treatment we still see a lot of curly leafs (cupped, distorted, stunted) and white secretion. This is because the insecticide uses an internal-agent.
Only after the insects have started nibbling, sucking end eating they get killed. But then at least the damage is limited to a minimum. The bottom photo shows the damage. This has opened after the insects have died, and in the best case will continue growing.