Pigweed , Palmer amaranth (http://plants.usda.gov/java/profile?symbol=AMPA ) was a major problem last year in bootheel agricultural systems.
As you recall, we had our first pigweeds up 13 April 2011 in Pemiscot County (https://bootheelagpestmanagement.wordpress.com/2011/04/13/the-pigweed-is-up/ ). The recent heavy rains, standing water, and early preemergence herbicide treatments all reduced the amount of pigweed in field. Today (9 May 2011), Jason and I found a new cohort of pigweed to be germinating. The best pigweed defense is a good offense, keep scouting your weeds!