Losing Fight Against Stiltgrass

Q: For the last few summers I’ve been fighting microstegium (Chinese stiltgrass) at our home. It grows in patches, takes hold randomly and spreads voraciously. I spray with a high concentration of vinegar frequently. But I’m losing the fight as more patches pop up and overwhelm the natives. 

A: The vinegar may kill the plant but the stiltgrass has probably dropped hundreds of seeds before it succumbs. You have to prevent seed germination to have any hope of control. Pre-emergent chemicals like dithiopyr, pendamethalin, or prodiamine will prevent microstegium seed from germinating. Since seed germinate throughout the summer, two applications (mid-February and early May) are appropriate. For a heavy infestation a third application in July might be warranted. Read and follow label instructions.