KC Gardens

Weeds are loving this rainy summer. If you don’t love them, here are tips for control

Chickweed Johnson County K-State Research & Extension

This summer is one for the record books. We experienced fewer uncomfortably hot, dry days followed by days with much-appreciated rainfall. Typically, non-irrigated lawns are a toasty brown, but this August has resulted in green, lush lawns.

September is the prime month for lawn care, especially seeding. The goal is not to reseed but maintain a healthy lawn that will flourish year after year.

Unfortunately, the rainy weather produced more weeds. Our office is receiving numerous inquiries about weeds and how to treat them. Whether to treat or not depends on the type of weed.

Here is your guide to combating those unwanted late summer weeds.

Annual weeds

Annual weeds will die as the growing season comes to a close and the first frost arrives. Tolerance is recommended this late in the season.

Both grassy and broadleaf weeds decline with shorter days and cooler temperatures. Timely mowing reduces their growth.

Pre-emergent treatments is ideal to control annual weeds, like crabgrass. These products control a wide range of weeds when applied in late March through early April to prevent establishment.

Broadleaf weeds escaping treatment can be spot sprayed with an herbicide in early summer.

Perennial weeds

Perennial weeds are difficult to control as they come back yearly. Treat when actively growing or in late summer as they are preparing for winter.

The hardest weeds to eradicate from a bluegrass and tall fescue lawn are perennial grassy weeds such as Bermuda, nimblewill and quackgrass. The reason is the lawn grass is killed in the process.

Timing is critical depending on whether the perennial weeds are cool or warm season. Treat cool-season grasses in the late spring or fall. Warm-season grasses are easiest to knock out in late July through August.

Bermuda or Zoysia in a bluegrass or tall fescue lawn is an issue. These grasses are best controlled now with the glyphosate (Roundup) herbicides. The ideal control window is late July through August.

Rainfall will make control easier as the grasses are actively growing. It usually takes more than one treatment to rid a lawn of perennial grasses.

Boost weed control by following these steps. Skip a couple of mowings to allow additional foliage and avoid treating stressed plants. Then spray the infested area. Wait a week and hit it again to ensure control.

Although this method kills the desirable turf, there is no waiting period between the application and reseeding. That means that the dead brown patch can quickly be repaired. Traditional broadleaf herbicides have a several week or more waiting period between applications and seeding. This makes controlling broadleaf weeds in late summer difficult if you plan to seed.

Before taking action to control weeds, know the weed and the timing for best results. This will ensure success when choosing the correct herbicide.

Dennis Patton is a horticulture agent with Kansas State University Research and Extension. Got a question for him or other university extension experts? Email them to garden.help@jocogov.org.

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