John Bruce commented on the use of "wetting agents" being beneficial with
Cygon--I'd concur on this, but I'd encourage looking for those that are
described as "spray surfactants," breaking down the surface tension of the
droplet while also working into the outer waxy cuticle of the leaf and
staying there (an old expression was "sticker/spreader").
The axiom "for every 10 degree (Celsius) increase, chemical activity
doubles" has some merit, but I'd rather not spray Cygon in the heat of the
day, but would prefer to when there is no wind, and at times when light and
humidity conditions would increase borer activity--it has some residual
activity, but it's best use is on the emerging larva.
Dimethoate (Cygon) was regarded for a time as the best miticide for row
crops, and I suspect that's where a great deal of its reputation as a
systemic comes from. There are better "larvacides" available, but I doubt
any will ever make it to the ornamental/residential/homeowner market(s)--as
I doubt any homeowner wants to see their pet sick, or have their backyard
smelling like a chemical warehouse.