Lawn Grassy Weeds

Grass Weeds In Your Lawn

by Roi Levin

One of the most troublesome group of weeds in Central Florida lawns are weeds in the grass family - generally, I refer to them as a group as "grassy weeds" from here on out. The most common grassy weeds are Crabgrass (we have five different species in Central Florida), Alexandergrass, Common Bermudagrass, Torpedograss, and Basketgrass. There are additional weeds in the grass family that infest lawns, but they are not as common or troublesome. In this article I'll dive deeper into the individual grassy weeds to give you a better understanding of what to expect if you encounter them in your lawn, or if your service technician notifies you that any of these are becoming a problem.

Management of Grassy Weeds is difficult and often not possible using selective herbicides - more on that later as this relates to specific weeds and turfgrass species. The best management options for weeds in lawns, including grassy weeds, are to follow proper maintenance practices that contribute to a thick, healthy lawn. Additionally, periodic renovation of areas that become infested by unmanageable weeds are sometimes necessary. These practices include:

Mow your lawn at the recommended mowing height for the species and variety.
Mow frequently enough that no more than 1/3 of the length of the grass is removed at any one time.
If weeds, including grassy weeds, are problematic in your lawn, remove clippings when mowing to remove the weed seed heads. Otherwise do not remove grass clippings when mowing.
Avoid transferring weeds, including grassy weeds, from one area of your lawn to another; Or if your lawn is mowed by a landscaper, between one property to another. I know - this is easier said than done!
Water your lawn frequently enough to prevent stress due to lack of water, and avoid watering when the lawn is water-healthy - this is probably the most frequent manageable issue that contributes to decline in lawns and in turn, predisposes the lawn to problems, including Crabgrass and other weeds, as well as fungal diseases and insect pests.
Fertilize the lawn properly for the turfgrass species - we provide proper fertilization services.
If soil pH issues are suspected, obtain a soil test from weaker areas of the lawn to determine if soil pH adjustments are needed - we provide this service.
If appropriate, apply preemergent herbicides to limit germination of Crabgrass and other lawn weeds - we provide this service if and when appropriate.
Hand-pull grassy weeds if they infest a small area of the lawn - my rule of thumb is smaller than about a Frisbee.
For small areas of Crabgrass and Alexandergrass infestations that cannot be hand pulled - management using baking soda is possible. Sprinkle a very thin layer of baking soda over wet infested areas. The application will burn off the leaves of the weeds and allow the surrounding lawn to heal into the area. Note that following application of baking soda, you will end up with an ugly brown spot in your lawn!
Larger areas of grassy weeds infestations in lawns should be killed using a nonselective herbicide such as Glyphosate. Following death of the weeds, remove the dead area down to bare soil. At this point we recommend to wait a few weeks for weed seeds to germinate, at which point you should apply nonselective herbicide again to kill the new weeds. Now you are ready to plant new sod into the bare area.

Crabgrass

Crabgrass (Digitaria sp.) is one of the most problematic weeds in residential and commercial landscapes. A number of years ago there was a selective herbicide available to professionals for legally-treating Crabgrass in residential St. Augustinegrass. While still available for purchase, this product cannot be legally-applied to lawns in residential or commercial properties, per the product labeling, which is federal law. Professionals and homeowners alike have been at a loss for a selective Crabgrass control method, particularly in residental St. Augustinegrass lawns. In Zoysiagrass and Bermudagrass there are several products labeled for management of some of the Crabgrass species.

Blanket Crabgrass

Blanket Crabgrass is probably the most common species of Crabgrass infesting lawns in Central Florida. It can be differentiated from other species of creeping Crabgrass species by the presence of hairs on the leaves and stems. This species is technically a summer annual, meaning it germinates in the summer and dies in late fall and into winter. However this weed hasn't read the textbook recently, and has become a short-lived perennial. Where we expected to see this weed die off during winter just a few years ago, these days we are definitely seeing it flourish in lawns through the winter. In St. Augustinegrass, our industry does not have a selective herbicide that we can use to treat this weed - in other words, there is no product that is effective to treat this weed without killing your St. Augustinegrass. In Zoysiagrass we can treat for this weed. Since this species of Crabgrass tends to linger in lawns and not die out annually, preemergent herbicides are not particularly useful for managing it.

For management recommendations for Blanket Crabgrass, follow the instructions under Management of Grass Weeds at the head of this article.

India Crabgrass

India Crabgrass is very similar to Blanket Crabgrass. They differ in that India Crabgrass lacks hairs on the leaves and stems. Like its counterpart, India Crabgrass hasn't read the textbook either, and tends to be a perennial in Central Florida. From a management perspective, this weed is very similar to Blanket Crabgrass.

For management recommendations for India Crabgrass, follow the instructions under Management of Grass Weeds at the head of this article.

Southern Crabgrass

Southern Crabgrass, Large Crabgrass, and Tropical Crabgrass are difficult to differentiate. Differences correspond to the location of seed head emergence from the grass stem. All three of these Crabgrass species are summer annuals - this means that they germinate throughout spring through summer and die in late fall to winter. While these species of Crabgrass can be troublesome in lawns, they are not as prevalent as Blanket Crabgrass and India Crabgrass. Preemerget herbicides can be quite useful to prevent these Crabgrass species from infesting lawns. Unfortunately there are no effective selective herbicides available for management of these Crabgrass species in St. Augustinegrass lawns. These weeds are manageable in Zoysiagrass.

For management recommendations for Southern Crabgrass, Large Crabgrass, and Tropical Crabgrass, follow the instructions under Management of Grass Weeds at the head of this article.

For additional information about Crabgrass, click here for information from the University of Florida.

Alexandergrass

Alexandergrass (Urochloa subquadripara) is one of the most troublesome grassy weeds infesting lawns. It is a perennial grass that germinates in the summer. Unlike Crabgrass, it persists through the winter. This weed is also sometime referred to as Tropical Signalgrass or Small Flowered Alexandergrass.

Alexandergrass management is very challenging in all lawn types due to several reasons:

Alexandergrass looks similar to St. Augustinegrass and is often overlooked before it overtakes large areas.
Preemergent herbicides (products labeled to prevent weeds) only manage Alexandergrass for up to eight weeks, so it readily germinates between preemergent herbicide applications.
There are no postemergent herbicides (products labeled for exisiting weeds) available for management of Alexandergrass in St. Augustinegrass in residential properties.
Postemergent herbicides labeled for Alexandergrass management in Zoysiagrass can cause severe stunting.

This lawn is made up of nearly entirely of Alexandergrass

Alexandergrass leaves and seed heads

For management recommendations for Alexandergrass, follow the instructions under Management of Grass Weeds at the head of this article.

For additional information about Alexandergrass, click here for information from the University of Florida.

Common Bermudagrass

Common Bermudagrass (Cynodon dactylon) is a thin-leaved, creeping perennial grass that is a very common weed in lawns. This is not the same Bermudagrass that is used in golf courses and sports fields.

Common Bermudagrass

Common Bermudagrass easily spreads by:

Creeping along the soil line via above-ground stems (stolons).
Creeping underground via below-ground stems (rhizomes).
Dispersion of seeds both naturally (wind, birds, etc.) and on maintenance equipment.

There are no postemergent selective herbicides available for management of Common Bermudagrass in St. Augustinegrass or Zoysiagrass in residental properties. Likewise, preemergent herbicides efficacy for Common Bermudagrass is very limited.

Managing Bermudagrass by hand-pulling is usually not effective, because unless the stems (both stolons and rhizomes) and roots are removed, then the weed will come back very quickly.

My recommendation for managing of Common Bermudagrass is to renovate the area if the infestation becomes intolerable. Kill lawn areas that are heavily-infested by Common Bermudagrass with a nonselective herbicide such as Glyphosate, which will kill all plants, including the lawn. Adding a grass-specific nonselective herbicide, such as Fluazifop, may provide better nonselective efficacy than Glyphosate alone. Following effective killing of the area, re-plant the dead sections with new sod. Note that it is likely that Common Bermudagrass will re-infest the area despite the renovation.

Torpedograss

Torpedograss (Panicum repens) is a perennial grass that frequently infests lawns in Central Florida. This weed is most prevalent in sites that tend to retain water, but not always. Torpedograss primary spreads by seeds and rhizomes (underground stems). The stems and roots are often prolific and deep, so physical removal is often very difficult or impossible.

There are no effective preemergent herbicides available for Torpedograss management. In St. Augustinegrass, there are no selective postemergent herbicides available for this weed. In Zoysiagrass and Bermudagrass, Quinclorac can be used with limited efficacy for management of this weed, but Torpedograss usually rebounds quickly.

My recommendation for managing of Torpedograss is to renovate the area if the infestation becomes intolerable. Kill lawn areas that are heavily-infested by Torpedograss with a nonselective herbicide such as Glyphosate, which will kill all plants, including the lawn. Adding a grass-specific nonselective herbicide, such as Fluazifop, may provide better nonselective efficacy than Glyphosate alone. Following effective killing of the area, re-plant the dead sections with new sod. Note that it is likely that Torpedograss will re-infest the area despite the renovation.

For additional information about Torpedograss, click here for information from the University of Florida.

Basketgrass

Basketgrass (Oplismenus sp.) is a summer-annual weed that is very common in shady areas of landscapes. There are two species in our area. Usually, this weed thrives in areas where turfgrass struggles. Basketgrass thrives in areas such as:

Under the canopy of Oak and other shade trees.
Along and under shrub beds that tend to stay shaded.
Along shaded structural exterior walls and fence lines.

Basketgrass is prolific and thrives on neglect during the summer months, and dies out in the winter. This weed will come back year after year from seeds deposited where it grows seasonally.

Basketgrass

Many homeowners express concern regarding this weed overtaking shady areas of their property. With that in mind, consider that this weed provides seasonal groundcover where a desirable lawn such as St. Augustinegrass, Zoysiagrass, or Bermudagrass will not grow, or will significantly struggle, due to lack to sunlight. It is my opinion that Basketgrass provides for a rather attractive groundcover in shady locations where turfgrass generally fails.

For those of you who are determined to suppress Basketgrass, a couple of options are available. You can apply Glyphosate, which is a nonselective herbicide (kills all plants). Be very careful of Glyphosate around desirable plants, as even a small amount can cause damage or kill any plant. Another management option for Basketgrass during the summer is with baking soda - sprinkle a very thin layer of baking soda over wet Basketgrass. Baking soda will result in a quick knockdown of Basketgrass, but this weed will rebound and additonal baking soda applications will be required to keep it suppressed. Again, my opinion is to leave this weed be, but everyone is entitled to their own preferences.

For areas where Basketgrass thrives and turfgrass fails, consider planting ornamental shrubs and groundcovers that typically thrive in shade. Such selections include, but definitely not limited to - Asiatic Jasmine, Liriope, Palm Grass, Azalea, and more.

For additional information about Baketgrass, click here for information from the University of Florida.