The pictures are too far away. Not sure if things are moving in there, if things fly away when you disturb the area or nothing is changes when disturbed. If nothing changes, it could be a bad case of powdery mildew. Some triangular shapes in the second picture made think of a whitefly infestation. There are, however, other possibilities. Amongst verbena pests, there are white aphids and mealybugs. Your best bet is to take a sample for identification to a local garden center using a sealed, transparent plastic bag.
Answered on July 8, 2021
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