Crabgrass control during a hot summer

Crabgrass has been enjoying the high temperatures in Michigan by invading turfgrass areas.

Crabgrass emerging in drought-stressed turf.

Crabgrass emerging in drought-stressed turf.

An up and down summer with stretches of drought alternating with buckets of rain has resulted in turfgrass divided into two categories: irrigated and green, or dormant, brown and now recovering. In either scenario, it is now very likely that crabgrass is making its presence felt.

Keep in mind that in contrast to our cool-season turfgrasses that have optimum growing temperatures of about 65-75 degrees Fahrenheit, crabgrass is a warm-season annual that will thrive in the high temperatures of 80-100 F. For dormant areas where irrigation has been applied to ensure complete crown dehydration and death do not occur, irrigation may result in some crabgrass emerging.

For these areas, controlling crabgrass is probably at the discretion of the turf manager or homeowner. Some might view the crabgrass as simply providing some green color to an otherwise brown turf. If post-emergence crabgrass control is in your plans, here’s a herbicide primer. Herbicides will be primarily referred to by their active ingredient.

There are two main options for post-emergence crabgrass control in cool-season turf: quinclorac (Drive XLR8) or fenoxaprop-ethyl (Acclaim Extra). Both products are effective for post-emergence control of crabgrass. However, there are also some key differences between these products (see table):

  • Quinclorac can boost broadleaf activity when tank-mixed with other broadleaf-specific herbicides, especially phenoxies like 2,4-D and MCPP.
  • Quinclorac can provide excellent control of some broadleaves, like white clover and dandelion, on its own.
  • Quinclorac can miss excellent post-emergence crabgrass control when crabgrass is at the two-to-three tiller stage.

When crabgrass is small (one-to-three leaf – one tiller) or when it is gorilla-sized (four tillers and over), quinclorac will provide excellent control of crabgrass and is very safe when applied to new cool-season turf seedings.

Fenoxaprop-ethyl is equally effective as a post-emergence crabgrass herbicide and differs from quinclorac in these ways:

  • Fenoxaprop-ethyl can be applied at any crabgrass growth stage and provide excellent control.
  • Fenoxaprop-ethyl can provide better goosegrass control than quinclorac.
  • Fenoxaprop-ethyl won’t provide any broadleaf weed control on its own and should not be tank-mixed with phenoxy herbicides.

There are other herbicides that can provide good post-emergence crabgrass control such as mesotrione (Tenacity) and topramezone (Pylex) and can be good choices in certain situations. Both of these products can be applied on the same day of seeding Kentucky bluegrass (be careful and read the label about applications on other cool-season turf species) for crabgrass control during establishment. Also, both can provide good control of some broadleaves as well. There are many tank-mix options available and warranted depending on the mix of weeds that may be present in different areas.

For homeowners, quinclorac is the most readily available product in formulated ready-to-use products. Michigan State University Extension advises you read these labels to find out how to best use them and in which situations they may be best utilized.

Comparison of quinclorac and fenoxaprop-ethyl herbicides

 

Quinclorac

Fenoxaprop-ethyl

Lose some post-crabgrass efficacy?

Yes – 2-3 tiller growth stage.

No – works well at all growth stages.

Stand-alone broadleaf activity?

Yes – particularly white clover, dandelion and speedwell.

No

Good tank-mix partner?

Yes – synergistic effect when mixed with phenoxy herbicides (2,4-D, MCPP).

No – do not mix with phenoxy herbicides as there is some antagonism.

Goosegrass control?

No

Yes

Turfgrass injury?

No – safe on newer seedings.

Sometimes – can injury some Kentucky bluegrass cultivars in high heat.

Dr. Frank’s work is funded in part by MSU’s AgBioResearch.

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