"What do farmers use to make crop…

A crop circle joke has been cited in print since at least 2009:

Q: What do farmers use to make crop circles?
A: A protractor.

Farmers usually use tractors. A protractor makes circles.

Wikipedia: Protractor
A protractor is a measuring instrument, typically made of transparent plastic or glass, for measuring angles. Most protractors measure angles in degrees (°). Radian-scale protractors measure angles in radians. Most protractors have 2 sets of numbers, the bottom set is for angles that open to the right and the upper set of the protractor is used to measure angles that open to the left.

They are used for a variety of mechanical and engineering-related applications, but perhaps the most common use is in geometry lessons in schools.

Twitter
Jesvin Vattamattom‏
@aitchnyu
How do farmers make crop circles? With a protractor.
7:02 AM - 2 Jan 2009

Twitter
Whitney Segura‏
@gardeningfun
Q: What did the farmer use to make crop circles?
A: A Protractor
10:25 PM - 29 Apr 2009

Twitter
Joseph Pearce‏
@joepearce
What do farmers use to make crop circles?——- A protractor!
9:23 AM - 24 Jun 2009

Reddit—3amjokes
How do farmers make crop circles? self.3amjokes
Submitted November 2, 2013 by Gabes_Bitch_69
With a protractor.
COMMENTS
Mogget8
I don’t get this is it an antijoke if so /r/antijokes

lackofbrain
Farmers drive tractors. People draw circles with protractors.

Google Books
Wildfire #1
By Matt Hawkins
Berkeley, CA: Image Comics, Inc.
2014
Pg. 19:
“HOW DO FARMERS MAKE CROP CIRCLES?”
“WITH A PROTRACTOR.”

YouTube
Jokes - What did the farmer use to make crop circles? A Protractor
jokesus
Published on Oct 2, 2015
Joke :
What did the farmer use to make crop circles?
A Protractor

Reddit—Circlejokes
What did the alien use to make crop circles? (self.circlejokes)
submitted June 20, 2016 by jimjamiam
A protractor

Reddit—Jokes
What did the farmer use to crop circles?
submitted November 27, 2016 by Barry2ba
A protractor

Reddit—Jokes
What makes crop circles?
submitted January 28, 2017 by EdwadThatone
A protractor.

Twitter
Edinburgh Festival Fringe‏
@edfringe
Q. What do farmers use to make crop circles?
A. A Protractor
#BadJokeFriday
9:09 AM - 29 Sep 2017

“What do farmers use to make crop circles?”/“A protractor.”