"The Annual International Wizard Gardening Competition, for example, caused many problems. So called 'crop circles', really entries in the Contorting Cereals class, caused sensation among Muggles worldwide"
-- from the report "A Study into Muggle Suspicions about Magic" (DP1)
This includes an event entry for Contorting Cereals, which has caused confusion for Muggles who see the results, calling them ‘crop circles‘. A report from a Ministry of Magic sponsored committee recommended that the International Confederation of Wizards ban this particular class from the annual competition (DP1).
If the crop circles are evidence of only one of the classes in the competition, how fantastic the other wizarding garden entries must be!
Although the date printed on the first Daily Prophet Newsletter (DP1) is 31 July 1998, the timeframe for this event is 1992-1993.
From the Web
Writing by J K Rowling on Pottermore: The Daily Prophet
Harry Potter Wiki: Crop-related charms