Below are two pictures of "black flag" symptoms on young cotton. These pictures were taken by Webster Harrell in Gates county. This is most likely due to plant bugs. Plant bugs on young cotton (particularly pre-squaring cotton) can take out terminals and cause this "black flagging". The threshold in Mississippi us 1 black flag per 10 ft of row.

My experience with plant bug damage to young cotton is that it is most likely to happen when it is dry and the plant bugs move off their preferred host to cotton. It is important to keep in mind that plant bugs are erratic. We don't need to overreact to this and spray all of our cotton just because we have seen this problem in one area. If you see these symptoms you should use a sweep net to see if plant bugs are still present. Overreacting could certainly help flair other problems as well as waste money if plant bugs are not present at damaging levels.