Controlling weeds is almost always a challenge. When do you control them? What do you treat them with? What are the specific label requirements? Most of these questions can be answered with a little bit of help from some good resources.
K-State puts together a good herbicide publication each year called 2017 Chemical Weed Control for Field Crops, Pastures, Rangeland, and Noncropland. The 2017 version is available on-line at http://www.bookstore.ksre.ksu.edu/pubs/chemweedguide.pdf
I often use this resource to see what herbicides are labeled for a given crop and for a particular timing (pre-emerge or post-emerge). Once I have that narrowed down, I look for more specific information the label will tell me like rates and restrictions.
Here are a couple of good on-line label sources:
Our K-State Research and Extension Agronomy web site has all these links and more in one spot. Check out their link at www.agronomy.k-state.edu/extension/weed-management