According to farmfutures.com in their weekly review, Urea prices on the international market spiked this week, up over $120 per ton. Futures were trending lower for the spring and summer months though, on hope that international supply issues could relieve some of the demand pressures - hopefully that leads to a pull back in pricing over the next couple months, but time will tell. As you know, ammonia pricing also impacts DEF pricing, and the good news is those prices eased some this past week or stayed relatively stable anyways, depending on the individual market. (you can read more about the specifics on the Urea & ammonia market movements here: http://farmfutures.com/story-weekly-fertilizer-review-0-30765 )
Since DEF is 32.5% urea, price swings on the market impact the price of DEF. Urea is also used in agriculture for nitrogen-release fertilizer, so usually we see spikes in demand (and price) along with agricultural schedules. This recent spike appears to be more supply related.