Summer is on the way out and as fall approaches, it’s time to start thinking about preparing lawns for a strong spring comeback. Turfgrass researchers don’t expect especially high pressure from weeds or diseases, but the hot and dry summer in many parts of the country has left lawns weak.
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“I don’t think there’s going to be any unique or major disease pressure other than the fact that if our lawn care operators aren’t diligent in trying to get those areas to recover, anyplace that a plant is weak is an opportunity, if moisture returns, for a pathogen to be opportunistic,” says Jim Kerns, turfgrass pathologist at North Carolina State University.
He says warm season grasses will bounce back once they get some rain, but cool season grasses are more at risk when the weather gets colder.
Jim Brosnan, associate professor of turf and ornamental weed science at the University of Tennessee, says the usual annual broadleaf and grassy weeds will be making an appearance this year. Last year, the wet September and October led to early germination of fall weeds, so many pre-emergent programs didn’t work as well as they did in past years. And it’s important to watch the winter weather to anticipate spring weed pressure.
“Last year, we had early germination, particularly of annual bluegrass, and then we went into winter and it got legendarily cold, as it has for two winters in a row now, and that really stunted the growth of everything. We had a lot of rain after that cold period and from that got a surge of winter annual broadleaf pressure and grassy weed pressure in late March, early April,” Brosnan says.
Kerns says germination will depend on whether your area receives a lot of precipitation or stays dry. He recommends aerating around Labor Day. “It can always help with recovery to get a good healthy stand of grass back, especially in cool season grass,” he says.
Kerns says cool season grasses should recover from winter weeds pretty well and operators should be able to get away with spot sprays or some broadcast applications for broadleaf weeds. For warm season grasses, many operators will need to wait to apply anything until the grasses go truly dormant in northern areas.
In order to do an effective pre-emergent application, Brosnan suggests scouting lawns in August. In his area, pre-emergent programs start around Labor Day, but that was too late last year. Cool weather grasses like tall fescue will be thriving this time of year, so it’s the ideal time to put down an herbicide. Just make sure the weather isn’t too hot and stressing the turf.
Scouting will make post-emergent applications more effective since smaller weeds are easier to control. “If you can come in and control seedling weeds that have just maybe newly germinated, that’s a much easier path than say coming into a lawn in March and trying to take out a mature common chickweed plant with flowers on it,” Brosnan says. “That’s just two different things.”
It’s key to treat winter annual weeds before they set seed back into the soil because once weeds have set seed, they have given themselves a foothold to come back the next year. “If we can control a weed before seed sets into the soil, we’ve at least done our part in reducing the weed seed percentage in the seed bank,” Brosnan says.
Brosnan also recommends switching up your control methods to avoid herbicide resistance, with annual bluegrass in particular, as he has seen an increase in treatment resistance.
This has been occurring on golf courses and sports turf, and while he hasn’t seen any cases in lawns yet, it is a threat. Continuing the same applications year after year reduces the tools in the tool box for weed control and can lead to complex and costly problems, he says. “There’s no point where diversification is bad.”
If you are applying an herbicide in the fall, make sure that you aren’t overseeding at the same time.