By Paul O. Johnson
Cool, dry conditions have slowed weed emergence and growth, but dry conditions also have limited the activation of preemergent chemicals. Given this scenario, fields need to be scouted closely to ensure that weeds do not get away. The time of warmer temperatures is coming, and once weeds have emerged with warm temperatures, it is just a matter of a few days before weeds are more than four-inches tall, and in dry conditions, they become very hard to control. If we get good moisture, the preemergent chemicals will be activated and provide their normal control.
The main concern is if the weeds have germinated before the preemergent chemical is activated, the preemergent chemicals, for the most part, do not control emerged weeds. Right now is the time to keep a good scouting program in place so there are no major weed control problems in the near future.
Source : sdstate.edu