By disabling AdSense for an ad unit, you'll likely reduce the number of advertisers that bid to appear on your site.
To disable AdSense for an individual ad unit:
In your DFP Small Business account, click the Inventory tab, then click Ad units on the left-hand panel.
Click the name of the ad unit that you'd like to disable.
Next to "AdSense inventory settings", click edit.
Clear the Maximise revenue of unsold and remnant inventory with AdSense tickbox.