The autumn season is no time to fall down when it comes to controlling and pre-treating weed pressure. And for southern lawns, the turn toward Labor Day provides little respite, with fickle weather patterns requiring a studied game plan.
The best time to control perennial broadleaf weeds is in the fall, rather than waiting until spring because you’ll get more active ingredients into the roots.
Prepping for autumn isn’t predicated on herbicides alone. Rather, your preemergence plan should combine applications with a review of spring data, along with study of irrigation systems, shaded areas and mowing heights.
Here are four weeds to get ready for as summer turns toward fall.
Annual bluegrass is a burden, to be sure. “The number one weed is Poa annua,” says Shawn Askew, associate professor of turfgrass weed science at Virginia Tech. “There are many different ways that Poa can cause problems … and now, in the southern states, there’s also a massive problem with herbicide resistance in annual bluegrass.”
To best control winter germination of Poa, LCOs need to have a plan in hand and the best bet for management is putting out a pre-emergence herbicide prior to seed emergence. The plan may also be well-served by rotating applications to avoid resistance.
From the Atlanta region and upward, Bermudagrass encroachment in tall fescue is often a problem. It can take two years of the fall schedule to remove Bermudagrass, or reapplication in the spring when grass emerges from dormancy. Reseeding in the fall can also help the issue.
A review of mowing heights can also help “Raise the mowing height,” Askew says. “You will never control Bermudagrass in tall fescue at 2 to 2.5 inches; you’ve got to get that mowing height up to 3.5 to 4 inches before you’re going to be successful with these chemical programs.”
“Application timing varies widely depending upon soil temperature and available moisture, but typically superintendents apply between September and October,” says Dr. Jay McCurdy, assistant extension professor of turfgrass sciences at Mississippi State. “After that, wintertime postemergence applications to control escapes are almost always warranted.”
After the spring emergence of crabgrass, goosegrass generally appears in bunch-growth a month or two later and is seen in areas receiving frequent irrigation.
While goosegrass treatment on greens is particularly delicate business, a lower mowing height, combined with herbicides can help LCOs get a grip on the goose.
Generally seen in high-cut turf areas and found with increasing regularity in the sub-tropical Southeast, the unseemly, blue and purple flowers of doveweed can proliferate when the plant goes to seed in the fall or through cuttings that are the result of mowing.
If the weed isn’t controlled heading into August, the population can worsen the following spring.
“Most broadleaf herbicides work well when it’s very young, but it is hard to scout for under turf canopy,” McCurdy says. “Unlike many other weeds, doveweed doesn’t care how dense the turf canopy is, or if you’re following all the right cultural practices, it just jumps up and smothers all the turf competition.”
LCOs can further dovetail the doveweed by attacking prior to germination in the spring.