Step 1: Separate the equipment by the type of field it works on. A puddler is designed to break down soil into a slurry under standing water, a step used only in wetland rice cultivation.
Step 2: Wheat fields are never flooded and puddled like paddy fields, so a puddler has no role in wheat production.
Step 3: The remaining three tools, disk harrow, shovel cultivator and reaper, all serve dryland operations of tillage, weeding and harvesting that wheat actually needs.
\[\boxed{\text{Puddler}}\]