Whats the chemical your using ?
Whats the label say ... concentrates are diluted and usually based on small ounces of chemical...
Applying the proper amount accourding to label is law everywhere! Federal and states !
Using excessive amounts of sokemchemicals wont be more effective but can contaminate the soil etc. ,, Round up is one of theose and ususally lasts around 2 days in the soil . I would use a max of 3 ounces per gallon .. other chemicals more or less depending on the application and calibration of the sprayer and nozzle rates lol ... there is more than meets the eye when it comes to chemical applications .. Try to follow the label for the application your using ...