Do I have to use an insecticide spray or will a detergent like Dawn be just as effective?
Timing is everything here. If you can apply a soap and water spray in early May before the characteristic leaf cupping damage occurs then you can reduce the population to a tolerable level if your soap and water can get good coverage where the nymphs are hiding.
Other recommended solutions are:
- do nothing, the damage is superficial and does not injure the plant
- prune out affected areas, you would probably be pruning your boxwood anyway
- pesticides are only recommended for severe infestations