No, not a good idea since the grub control needs to be watered in with 1″ of water and weed killer need to sit on the leaves of the weeds for at least 24 to 48 hours to work before it gets washed off. Id apply the grub control first then do the heavy watering. While the lawn is still wet from that watering, apply the weed killer. This will help the granules stick to the leaves. If you are using liquid weed killer, you can apply it anytime the nighttime temps are 50° reliable and when rain isn’t expected for at least 24 hours after application.