Garden News: Controlling weeds in late summer can be tough

“A thick healthy lawn works a lot like mulch in a flower bed, suppressing the growth and weed establishment,” says LSU AgCenter turf specialist Ron Strahan. “Unfortunately, our lawns have been recovering from a very difficult winter and are thinner than usual. Advantage: weeds.”

Weeds are opportunistic and have taken advantage of less-competitive lawns, Strahan says.

A weed that has really gotten out of hand this summer is Virginia buttonweed, which is a mat-forming summer perennial with rapidly spreading branches. It ranks as the No. 1 weed problem in Louisiana lawns.

“Yards are full of buttonweed right now, and it has become well-rooted and established since emerging in late March,” Strahan says. Once the plant matures, it actually can kill your lawn by forming a mat that chokes out the turfgrass.

At this point in the growing season, control is extremely difficult. These mature buttonweed plants have been hardened off. They’re flowering and starting to produce seeds for next year.

Typical over-the-counter lawn weed killers have a strong potential for injuring lawns in the high heat and humidity we have now, Strahan warns. The best approach now is removing by hand as many plants as possible.

If you choose to spray them, the LSU AgCenter recommends two professional herbicides that will suppress the growth of late-season Virginia buttonweed — metsulfuron (Mansion, Manor, MSM Turf) and Celsius herbicides.

These herbicides may not be available at typical retail nursery outlets, Strahan says. However, they can be purchased at stores that sell professional turf and landscape products throughout southeastern Louisiana.

You asked

Can I trim hawthorns now? Can I trim redbud trees now or do I have to wait for a certain time? ­— Margo

Shaping and light pruning of Indian hawthorn should be conducted in late spring after flowering is completed. Any pruning on redbuds and similar, smaller spring- and summer-flowering trees should ideally be done during winter. — Allen Owings, LSU AgCenter horticulturist.

Got a gardening question? Write to GardenNews@agcenter.lsu.edu.