Do you know the name of them? That might be helpful. Not for me as I know nothing about them but even a description if you don't know the name might get you some really good feedback, that's all.

Have a look really close and inside the growing tips to see if they're infested. Tip burn can also result from hot, dry conditions and too much salt (like fertilizer) in the soil.

Have you used any weed killers lately? Maybe used Weed N'Feed type product on the lawn?