A website from UGA Cooperative Extension

If you are having issues with crabgrass, sandbur, johnsongrass, or other grasses in your bermudagrass hay field you can make a one-time application of glyphosate after your first cutting. This method is a very time sensitive though. You need to spray the crabgrass/sandbur after it has begun to grow, but before the bermudagrass has really greened up. This is a tight window because you must cut the hay, bail it, and get it moved off the field before you can spray. An approximate time window would be spraying this application three to five days after cutting the hay. So, if you have rain and you cant get the hay bailed until a week later you are not going to be able to make this application. The rate for this application is 10 oz of 5.5/lbs per gallon of active ingredient so make sure you check the strength of the product you have they can vary from 40-55 percent. Please see the instructions from the UGA Pest Handbook below.

Glyphosate (Roundup PowerMax) 5.5lbs/Gallon – 10 oz per acre

REI/PHI – 4 hrs

Apply after the first bermudagrass cutting when bermudagrass has not yet initiated regrowth. Controls crabgrass, field sandbur, seedling johnsongrass, and most annual grasses. Applications made after regrowth has begun will damage bermudagrass. DO NOT graze or cut for hay for 28 days after application. Make only 1 application per year. DO NOT make an application after the first cutting if the field has previously received a glyphosate application during the winter months.