Can you drive a semi with trailer that is licensed with farm without cdls that is under 26000lbs?

The 26,000 lb. weight limit isn't applicable to what the vehicle weighs at the time, but rather, the weight rating of the vehicle. If you're talking about a Class 7 or Class 8 power unit, the weight rating of the power unit alone will be in excess of 26,000 lbs, before you even factor in the trailer.

As for the farm truck exemption to needing a CDL, it has limitations:

• The vehicle must only be used for purposes of that farm, and not on a for-hire basis for a third party
• The operator must be the farmer, an immediate family member of the farmer, or a direct employee of the farmer
• The vehicle must be operated within a 150 road mile radius of the farm it belongs to
• It must be registered as a farm truck