Here is a seasonal trend site that shows the historical trend of Corn that typically tops out in June and much the same with Soybeans with a downtrend after. Check out the Wheat seasonals as well as they trend much differently. This is just one multi year line chart but Moore Research uses 3 different time frames overlaid to see the changes that may have developed within each time frame. It is best to see all 3 time frames match each other within reason otherwise some structural change has taken place. They tend to match most of the time within reason.