Weed Control in Dormant Buffalograss

Q. We have Buffalograss for a lawn which we overseed every winter with ryegrass. We applied the ryegrass late this fall and it didn’t come up, but  weeds did. Now our Buffalograss lawn is covered in weeds. Is it possible to apply a “Weed and Feed” product to kill all the weeds and not hurt the Buffalograss?  If so, what would you recommend and when should this be applied?

Weeds growing in Bufflograss not overseeded.

Closeup of the weeds. Many very early spring weeds are winter annuals like the mustards. They are easily killed but don't let them go to flower and seed!

A. Buffalograss, like Bermudagrass, is considered a “warm season grass”. It is native to the Great Plains of the US has a reputation for low water use. All warm season grasses are brown in the winter because they are dormant due to cold weather. As their name suggests, warm season grasses prefer growing in warm or hot climates. Besides Bermudagrass and Buffalograss, other warm season grasses include zoysia, Paspalum, and St. Augustine grass among others. These grasses are sometimes called “southern grasses” because they are used primarily in southern states.

            Warm season grasses start turning brown in the cool fall months sometime in November and are totally brown here by December. Seeding a “cool season grass” like ryegrass into a “warm season grass” as its transition to dormancy is happening, creates a green winter lawn. You have two lawns in one during the winter; a green lawn actively growing in a brown lawn that is “sleeping”. The key for successful “winter overseeding” is good timing. A winter lawn of cool season grass is seeded as weather begins cooling off in the fall but you can’t wait until it’s cold.

            The time for winter overseeding in this climate is between the end of September and mid-October. Your November timing was too late. If you have a warm November it’s possible to make it but that’s not what happened. Last November was a cold month with unusually freezing temperatures around midmonth. It was too cold for successful overseeding.

            Estimating when to overseed a lawn is like estimating when to put out tomatoes in the spring only in reverse. Pay attention to the current weather and weather predictions for the coming two weeks. If it’s unusually warm, delay overseeding a couple weeks. If a cold front is coming in then you better get busy and overseed.

            Warm season lawns like Buffalograss start to “wake up” and grow when it gets warm; March or early April here. Since the Buffalograss is dormant now (brown) any weed killer that kills green growth will not harm the dormant lawn. The usual weed killer used for this purpose is glyphosate. Mow these weeds but apply the weed killer in early March. A week or so after this weedkiller has been sprayed, mow the lawn short, fertilize and water it to encourage faster green up.