Nearly 300 lawnmowers were stolen from a lorry parked in a lay-by on the A1 near Pontefract.
Police said the incident happened between 12.50am and 8.30am on Friday, May 16 at Barnsdale Bar on the northbound carriageway.
Thieves cut the curtain of the trailer and took 288 lawnmowers.
Det Con Andrew Hicks of Wakefield CID, said:“The total value of the lawnmowers is considerable and I would appeal to anyone who witnessed the incident to come forward.
“If you are offered a lawn mower for sale from a non-reputable dealer then stop and think - if the deal sounds too good to be true then it usually is.”
Anyone with any information should contact police on 101 or Crimestoppers, anonymously, on 0800 555111.