Ask the Superintendent – Weed Control

Greetings avid golfers and turf fanatics! With the New Year well underway and plenty of distractions in our day to day lives it’s easy to forget that it’s Spring Pre-emergent weed control season. So as we enter the second year of writing the “Ask the Superintendent” column and after nearly 40 years of watching people miss the weed control window in the Spring, I wanted to commit to writing a beacon of hope for a great summer lawn column published every February. That said, the crux of the query from every turf focused member and home owner this time of year should be, “How do I control the weeds in my lawn”? So avid golfers walk with me through the critical steps as we answer this most ardent and timely of questions and set you on the path to a better home lawn. 

First things first

It is important to know what type of turf grass you have in your lawn before you start developing a weed control program. Common turf grass types in North Texas include Bermuda grass, Zoysia grass, Saint Augustine, centipede grass and Fescue to name a few. Each type of grass has different light, soil and fertility requirements as well as growth and environmental factors so knowing that you have picked the best suited grass for your lawn’s environment is important. Healthy turf is the first step in controlling invasive weeds. A healthy base turf can suppress many weeds before they can establish themselves in the sward (turf stand). If you have the right grass in place we will move on to defining what a weed is and how to control weeds that will eventually challenge your desire for a beautiful lawn. 

What is a weed?

What exactly is a weed anyway? For our purposes today we will define a weed as a plant growing where it is not wanted and in competition with desired/cultivated plants (lawn). So essentially any plant that is growing where it is not wanted is a weed so Bermuda grass growing in a Saint Augustine Lawn is considered a weed. In terms of lawn or turf weeds, they come in two basic groups, winter, or cool season weeds (henbit, chick weed and poa annua or common meadow grass to our friends from the UK) and summer or warm season weeds (goose grass, crab grass and nutsedge). These weeds begin to germinate at different times of year. The cool season grasses in late summer early September through October and the warm season grasses from mid-February through May. There are two basic approaches to weed control, physical and chemical. 

Physical weed control is simple you literally remove the weed physically. This is often impractical depending on the number and establishment of the weed population. Chemical weed control is achieved through the use of herbicides (an agent, usually chemical used to kill plants). Herbicides also come in two primary groups, preemergent and post emergent herbicides. Preemergent herbicides are applied BEFORE (thus the urgency in the Spring Edition weed control article) the weed plant germinates killing the plant just after seed germination before a root can establish in the soil. Post emergent herbicide is applied to existing weeds and often require direct contact to be effective. 

There are a few preemergent herbicides that have some post emergent characteristics but by in large you will make the choice of herbicide based on the time germination of the weed. Post emergent herbicides can also be selective (kill certain plants but will not harm others) and non-selective (will kill or damage most plants that contact the product).  

Timing is everything!

It is critical that a preemergent herbicide be applied properly and at the right time of year to be truly effective.  So now is the time to apply preemergent to control summer or warm season weeds, starting in February. We will not go into all the factors that affect weed seed germination just know that preemergents are most effective if they are applied before the weed seed germinates. In fact, preemergent herbicides prevent the germination of weed seeds by inhibiting a key enzyme and should be applied Spring and Fall to provide year-round weed protection. It is important that the herbicide make good soil contact to be effective so watering in the product is recommended. Most homeowners will likely choose a granular preemergent which can be purchased from your local nursery or garden center. Below are some effective options. 

Prodiamine (Barricade equivalent) is the longest-lasting, and most economical due to lowest application rates.

Isoxaben (Gallery equivalent) prevents a very large list of Broadleaf Weeds. …

Oxadiazon (Ronstar equivalent) is a great granular option – safe in all turf and ornamentals. 

Once you have purchased your product simply follow the instructions on the product label that is attached to the bag/container. If you have questions or want the latest tips on turf grass in Texas the Texas A&M Agrilife Extension program can help either online or by phone. To improve your results you may consider making a spilt application of the herbicide. This involves making two applications at 50% of the recommended product rate. This allows one application early in the season and a second several weeks later to offer a larger window of control without over applying the active ingredient of the herbicide. If you are making a granular preemergent herbicide application here is a quick reminder of how to calibrate your rotary spreader.

How to calibrate a rotary spreader

Determine the amount of fertilizer/product needed for 100 sq. ft. For example, the fertilizer bag weighs 50 lbs. and covers 10,000 square feet per the label recommendation

Place this amount in the spreader.

Mark off the area. For a rotary spreader, use a 10-foot by 10-foot area (100 sq. ft.).

Apply using the suggested label setting to the test site

Adjust the setting up or down based on the actual amount of fertilizer applied, if you covered the area completely with nothing left in the spreader you are perfect! If you have product left in the hopper increase the spreader setting, if you run out of product before the area is covered then decrease the setting. Repeat this process until you find the correct setting. Take notes for future reference

Complete the application for the rest of the lawn 

One last thing

Weed control is an ongoing process of controls and actions that strengthen the base turf grass and eliminate invasive plants. It is February so if you see mature weeds in your lawn they are winter weeds (see paragraph three) and will not be killed by a preemergent herbicide applied now. Just remember that the Spring preemergent application prevents Summer weeds and a Fall Preemergent application prevents winter weeds. There are no 100% effective preemergent weed control products available so using some physical removal and post emergent herbicide applications are also required to be most effective. Be diligent, safe and keep reading Avid Golfer magazine and your perfect lawn will soon be a reality.