Pre Emergent Herbicide for St Augustine Grass

St Augustine grass, also known as buffalo or carpet grass, is a great turf choice for the warm seasons because of its dense coverage, sun tolerance, and sturdy blades. Like most lawns, St Augustine will provide some natural protection against weeds the thicker the coverage is, but that’s only part of a bigger strategy that also includes applying pre emergent herbicide before the grass revives in early spring.

If any weeds do end up growing in a St Augustine yard, it can be difficult or impossible to remove certain types of them.

How Does Pre Emergent Herbicide Work?

Herbicides that are applied to prevent seeds of weeds from germinating are known as “pre emergent,” and those formulas that target plants that have already sprouted or grown are called “post emergent.” Pre emergent weed killer is usually applied right before your desired grass grows in to make sure the ground is prepared for when the temperatures reach the warmth to reawaken your grass.

Many herbicide formulas are made to target certain types of weeds, like grassy and broadleaf weed species, or more specific formulas like crabgrass preventers, and are made to be safe to use on particular types of grass. When you’re looking for an effective pre emergent product for your St Agustine lawn, the active ingredients you want to see include:

  • prodiamine
  • dithiopyr
  • pendimethalin
Quali-Pro Prodiamine, Pre-Emergent Herbicide, 5 lbs, Yellow Granules
  • PRE-EMERGENT HERBICIDE: Quali-Pro's Prodiamine 65 WDG provides pre-emergent grass and broadleaf weed...
  • FEATURES & BENEFITS: Excellent tank mix partner with fertilizers and iron solutions
  • USE SITES: Nurse, Landscape, Turf, Trees, Golf Courses
  • EFFECTIVE AGAINST: Annual bluegrass (Poa annua), Henbit, Knotweed, Chickweed, Spurge, Foxtail,...

These are known to not interfere with the St Augustine germination process, and targets grassy weeds like crabgrass to suppress them before they can sprout.

Can You Put Pre Emergent on St Augustine?

Pre emergent herbicides should be applied before your St Augustine grass grows in the spring. This is because the grass will come in thicker if it doesn’t have to compete with other unwanted grasses or plants. Applying a pre emergent weed killer again at the end of the summer season before fall growth begins will help keep any new weeds from establishing themselves over winter or dropping seeds for the next growth cycle.

If there are other plants present or starting to grow, they can crowd out, or mix into, the St Augustine lawn and make it difficult to remove them. Using a weed killer that keeps weeds from growing in the first place is the easiest way to allow your desired grass to fill in from the start of the warm months.

The growing season for St Augustine will be different based on your location. The grass is classified as growing best in USDA Zones 8-10, but it will be happy to grow wherever soil temperatures remain above 60 degrees for several months. This means you should apply pre emergent herbicide when the soil temperature is consistently around 50-55 degrees, or after the last frost.

St Augustine Growth Patterns

St. Augustine Grass

St Augustine lawns are perennial, and a healthy root system will grow back each year for several years. This grass is known as a spreader because it grows across the lawn by above-ground root offshoots called stolons. This warm season grass is loved for this characteristic: it fills in yards well as it naturally wants extensive coverage for maximum sunshine absorption.

St Augustine can be complimentary to some warm season grasses like Centipede, Bermuda, or Bahia, but certain unwanted groundcover can grow in with it as well. Typical weeds found in St Augustine yards include:

  • clover
  • rye
  • Kentucky bluegrass
  • crabgrass

These deep-rooting grasses are spread by seed, and can easily work their way between the St Augustine stolon system and wait for the next growing season to sprout. The cool season grasses like rye and bluegrass will grow well into spring and will still be present during the St Augustine’s emergence period.

Once they do disappear, warm season weeds like crabgrass may take advantage of the spaces left open when those other annual weeds die off.

Can You Fertilize And Apply Pre Eemergent At The Same Time?

A pre emergent herbicide application can easily be coupled with a fertilizer application just before the beginning of the spring growing season. Many weed and feed formulas contain a blend of targeted weed herbicide and the NPK macronutrients (nitrogen, phosphorus, and potassium) to be available to the plant as it grows.

Scotts Turf Builder Lawn Food, 12.5 lb. - Lawn Fertilizer Feeds and Strengthens Grass to Protect Against Future Problems - Build Deep Roots - Apply to Any Grass Type - Covers 5,000 sq. ft.

Clearing out unwanted plants right before the grass starts to come in will allow it to grow and spread as densely as it can, which itself helps suppress weed growth. A turf with a healthy amount of thatch, dense roots, and full blade coverage won’t allow much light to penetrate the soil, and the lack of space won’t give any germinated seeds room to grow. 

Keeping Your St Augustine Lawn Weed Free

Aside from herbicide, keeping the lawn in its healthiest condition is an important line of defense against weed growth. St Augustine grass is loved as a warm season grass for its hearty nature, which informs on how to best take care of it:

  • It’s sun-loving – This warm weather turf grass can tolerate full sun as well as some shade, so it is a favorite for sprawling lawns at home, near beaches, or on golf courses. It will spread out to take advantage of as much light as it can.
  • St Augustine likes to be kept moist – Since this grass spends so much time in high temperatures, it’s important to keep it evenly water Too much water, however, can promote root rot or fungal growth in the soil, so be sure not to overdo it.
  • It likes well-draining soils – St Augustine is used to soils with a relatively neutral pH of 6 – 7.5, since it’s used to moisture-retaining but well-draining soils that might have a higher salt or sand content than other soil

How To Deal With Widespread Weeds That Continue To Emerge?

Dandelions and Lawn Weeds

If your St Augustine has weeds growing in it despite your best efforts, it can be a good idea to till the yard and plant sod over it. This will help churn any seeds that may be present, while the layer of sod will provide thick grass cover that will block any seeds from light without the need to compete with any existing grass for presence. Any undesired seeds will also be less likely to shift and move to the surface level.

Topdressing the soil with new soil and compost periodically is another way to suppress weed growth and promote a healthy lawn. This will build the topsoil depth and bury any potential seeds that may show up. When you topdress the mature yard lightly at different points in the year, it will build the soil without getting in the way of your lawn’s own growth pattern.

Last update on 2024-05-30 / Affiliate links / Somes Images and Data from Amazon Product Advertising API