This happened in a matter of days. Lawn guy just treated "trees and shrubs" and put down an insecticide.

These were planted in February this year and have looked incredibly healthy up to this point.

Please don't be Oak wilt.

Phytotoxicity is a suspect, esp. among younger trees ...
if the current Texas Oak Wilt problem wasn't already in the works, ready to pop out.

e.g.
A highly recommended "dead bugs all round and never came back!" - by an enthusiastic top homebuider - pest control company came out as a trial. No wonder these accolades. His mantra was - use a gallon of poision when only jigger is required and spray it EVERYWHERE.
We simply couldn't have this around pets & kids.

FYI - this may not be related as to cause but perhaps a good idea as to immediate remedy that shouldn't hurt

Thought Cannas (potted & in garden) might use a bit more water since last rain was a week ago.
While filling up bird bath (sign of watering needs) got bright idea to hose spray cannas as a treat.
Next day some leaves turning brown, very uncommon.
Aggieland tap water is high in sodium, always been. Gets worse in summertime, more so if supply line is at end of street!
Lucky to have a small stock of rainwater, to drench leaves & soil, hoping to leach salts out.
Next day, things are improving!
History tells me R.O. water is almost as good ... almost. Better than nothing, cheaper than bottled Spring water!

put a tree water bag around it. Fill it up 2 x per week about 3-4 days apart. It needs water