Completely understand the crop to be planted, rotation to sensitive crops and tillage practices. There are several good identification manuals available. However, our 23 Certified Crop Advisors are pretty good at identifying weeds species. Some of the chickweeds are pretty far along in their lifecycle with the seeds already forming. This makes it much more difficult to control at the normal rates, so a higher rate may be required to provide adequate control.
Heavy infestations require higher rates or higher carrier volumes to achieve adequate control.
Also, dense weeds infestations sometimes take longer to die back so planting may be delayed depending upon herbicide or tillage selection. Many of the herbicide tolerant crop varieties or hybrids can be managed a little differently than the non-tolerant ones. And some herbicide programs can affect next years crop growth and development. Understanding all this plus the biology of the weeds will produce the best management strategy.