The basic mixing rate for Bifen IT is 1 oz per gallon of water. This is the best rate for termites, and also for general pest control indoors. Outdoors, reduce the rate to 1/2 oz per gallon of water and spray the grass or plant surface until wet. Here is a link to the Bifen IT label
If you are treating plants, I would recommend to mix Bifen IT at 1/2 oz per gallon of water. Use the gallon of mix as you normally would, and then calculate how many gallons of mix you will need to treat the entire 3500 plants. 1/2 oz Bifen per gallon of water will generally treat around 1000 sq feet of space.