Turf herbicide selection plays a critical role in herbicide performance. For example, some turf and lawn herbicide formulations damage certain turf varieties, while others are selective and don’t affect turf at all. That’s why it is essential to choose products that are for use on the specific turfgrass species.
 
 
 
 
Several factors impact the effectiveness and performance of turf herbicides:
 
  1. Herbicide selection
  2. The target weed species,
  3. Application timing
  4. Environmental considerations.
  5. How are you applying it?
  6. Environmental considerations.
  7. Herbicide resistance
  8. Turfgrass tolerance
  9. herbicide formulation
  10. Planning ahead

Herbicide Selection

Herbicide selection plays the biggest role in how a herbicide performs and the results you get. Herbicides have different modes of action, which affect how well they work against weeds. Factors such as pre-emergent or post-emergent activity, selectivity, and soil longevity all play a role in choosing the right herbicide.
 
 
Selecting herbicides with different modes of action is essential for herbicide resistance management  and using the same herbicide repeatedly can lead to the development of weed resistance. By rotating herbicides with different modes of action, you target weeds in multiple ways, reduce the resistance risk and improve long-term weed control.
 
 
So for those of you who rotate Destiny herbicide, Duke herbicide, Coliseum herbicide, Tribute herbicide  and Monument herbicide or Recondo herbicide. Stop, as these are different actives but all sulfonylureas!

Target weeds

Different turf and lawn herbicides target specific weed types in turf grass. How well a herbicide works varies and depends on what weed is present. Some herbicides are more effective against broadleaf weeds, while others target grassy weeds.
 
 
This means that correctly identifying the weed is crucial. After this you can then select the correct herbicide that will control this weed. Using the wrong herbicide for a particular weed species will result in inadequate control or be a complete waste of time and money.
 

 

Ways in which the target weeds impact herbicide performance:

Sensitivity:

Different weed species have varying levels of sensitivity to herbicides. Some weeds are susceptible to a particular herbicide, while others are more tolerant. For example, pigweed can be tolerant to 2,4-D compared to other broadleaf weeds.

Mode of action:

Some herbicides may target specific biological processes or enzymes that are unique to certain weed species. If the target weed species lacks the target site or mechanism of action, the herbicide may not work against that particular weed.

Dicamba is a broadleaf herbicide that primarily targets sensitive broadleaf weeds by disrupting the growth and development of plant tissues. However, oxalis may exhibit tolerance to dicamba, so you get poor control when you use this.

Growth stage:

How well a herbicide works against a target weed is also a result of its growth stage. Certain herbicides are most effective when applied at specific stages of weed development.

For example, quinclorac works well vs juvenile and mature summer grass weed but not so well when it’s at the 2-4 tiller stage. So applying a herbicide at the wrong growth stage may result in poor results.

Glufosinate is another example. When you use this as a non-selective herbicide for broad-spectrum weed control, it works best on young, actively growing weeds.

Weed size:

The size of the target weed can also influence herbicide performance. Larger and more developed weeds tend to have thicker cuticles and extensive root systems. These affect herbicide absorption and translocation within the plant. Some herbicides may be less effective on larger weeds due to reduced uptake or limited movement within the plant.

Resistance:

Weed species that have developed resistance to specific herbicides pose a significant challenge.

Application Timing

Herbicide application timing is critical. Some turf and lawn herbicides like pre – emergents are more effective when you apply before the target weeds have germinated. Others are post emergent for use when weeds are actively growing. Selecting herbicides that align with the appropriate application timing for the target weed species is crucial for achieving maximum control.
 

Some examples of application timing impacting herbicide performance:

Weed growth stage:

Different herbicides are more effective at specific stages of weed growth. Timing the herbicide application when the target weeds are in their most susceptible growth stages can lead to better control. For example, some herbicides are more effective when applied to young, actively growing weeds, while others may be more effective on mature weeds. Applying herbicides too early or too late in the weed’s growth cycle can result in reduced efficacy.

Turfgrass Growth stage:

Certain herbicides may cause damage or stunting to turfgrass if you use them at the wrong time.

Environmental conditions:

Environmental conditions at the time of herbicide application can also impact performance. Factors such as temperature, humidity, and rainfall can influence herbicide absorption, translocation, and degradation within the target weeds. Applying herbicides during unfavorable weather conditions, such as high temperatures, drought, or heavy rainfall, may result in reduced herbicide efficacy or potential off-target movement.

Weed size:

The size of the target weeds can affect herbicide performance. Some herbicides are more effective on small, actively growing weeds, while others may require larger weed sizes for optimal absorption and translocation within the plant. Applying herbicides too early when the weeds are too small may result in inadequate control, while applying them too late when the weeds are too large can reduce the herbicide’s effectiveness.

Repeat applications:

Some herbicides like MSMA or Poacure require multiple applications or follow-up treatments to achieve effective control. The timing of these repeat applications is critical. Herbicides often have specific intervals between applications to target weeds at different growth stages or to control emerging weeds.

Environmental Factors

The Temperature, humidity, rainfall, and wind speed can all affect the absorption, translocation, and degradation of turf herbicides. Herbicide choice should take into account environmental factors, such as the proximity of sensitive crops, water bodies, or wildlife habitats.
 
Some herbicides have specific restrictions or require buffer zones to protect non-target plants or aquatic environments. An example of this is on the Poacure herbicide label which goes to the extent of having a buffer zone table on the label.
 

Environmental conditions affecting herbicide performance:

Temperature:

Temperature has a big influence on herbicide performance as some herbicides require a specific temperature range for optimal performance. A great example of this is if you use diclofop methyl to control Crows foot grass. The Destro label specifically states DO NOT apply if temperatures are above 25C. High temperatures speed up the breakdown rate of some herbicides, and so stop them working as well. Conversely, low temperatures tend to slow down herbicide activity. This is the case with the sulfonylureas which includes Duke herbicide, Recondo herbicide and Tribute herbicide. When you use any herbicide, make sure it is within the recommended temperature range to get the best results.

Humidity:

Higher humidity helps herbicides stay on the plant surface longer, and so enhances absorption. This is especially important for foliar herbicides. During hot, humid conditions spray droplets evaporate slower. This means any spray takes longer to dry and so increases herbicide absorption.

Absorption and translocation of bentazone in turfgrass increases in humid conditions1Kudsk, P.; Kristensen, J. Effect of environmental factors on herbicide performance. In Proceedings of the First International Weed Control Congress, Melbourne, Australia, 17–21 February 1992; Weed Science Society of Victoria: Victoria, Australia, 1992; pp. 173–186. This is due to the cuticle being hydrated, which encourages herbicide absorption2Matzenbacher, F.O.; Vidal, R.A.; Merotto, A.; Trezzi, M.M. Environmental and physiological factors that affect the efficacy of herbicides that inhibit the enzyme protoporphyrinogen oxidase: A literature review. Planta Daninha 2014, 32, 457–463..

Hot, dry conditions have a greater impact on systemic herbicides than contact type products. However, excessively high humidity or prolonged periods of leaf wetness can lead to herbicide runoff or wash-off before uptake can occur. In hot and dry conditions the use of the right spray adjuvant and surfactant is even more important.

Adjuvants and surfactants aid herbicide uptake by enhancing spray droplet retention on the leaf surface, dissolving wax cuticles, and holding spray droplets on the leaf for longer by reducing the evaporation rate.

Rainfall:

Rainfall or irrigation shortly after herbicide application can impact herbicide performance. Heavy rainfall or irrigation can cause herbicide runoff, dilution, or leaching, reducing the concentration of herbicide available for weed control.

  • S-metalochlor present Pennmag (Syngenta) can quickly move out of a sandy soil profile after heavy rain, due to its relatively high solubility in comparison to pendimethalin.

Wind:

Wind can affect the application of herbicides by affecting the spray pattern and distribution of herbicides. Strong winds can cause herbicide drift, leading to non target deposition of herbicide droplets or particles. Herbicide drift can result in damage to desirable plants, crops, or adjacent sensitive areas. That’s why you use drift control agents to reduce spray drift by increasing the size of spray droplets. These work by increasing the average droplet size and achieve this by binding with water molecules to form larger spray droplets

Soil conditions:

Soil conditions can have a big impact on herbicide performance. This is especially the case with soil-applied herbicides such as pre-emergents. Factors such as soil moisture, organic matter content, and pH can impact herbicide availability, absorption, and degradation in the soil. Additionally, soil texture and structure can affect herbicide movement.

  • Foramsulfuron (Tribute herbicide) efficacy on crows foot grass is greatest under conditions of high soil moisture and high evaporation, and may be reduced in sandy soils.
Dicamba herbicide drift onto non target plants

Correctly Applying

In order to get the best results from a turf or lawn herbicide you need to make sure that you apply it properly. Factors like the spray volume you use, the spray droplet size, and the nozzle selection, are all important to achieve thorough coverage and minimize drift.
 
 
An example is the use of dicamba and any herbicide formulations containing this, like Methar Tri Kombi. Dicama is a selective herbicide used for broadleaf weed control in turfgrass. Drift onto non-target areas, such as ornamental plants or sensitive vegetation, can cause damage or injury.
 
So it is crucial to consider wind speed, direction, and the use of buffer zones to prevent spray drift and protect non-target plants.

Herbicide resistance

If you rely on a single turf or lawn herbicide or one particular group, weeds can develop resistance. This means these herbicides and all those in their herbicide group become ineffective and stop working. You can slow down resistance developing, If you rotate herbicides modes of action and also use integrated weed management.

Turfgrass Tolerance

Turfgrass tolerance is the ability of turfgrass to withstand turf and lawn herbicides without any significant injury or damage. This herbicide tolerance is crucial in ensuring that a herbicide targets the weeds without causing harm to the turfgrass. A tolerant turfgrass species or cultivar will withstand the herbicide application, allowing for selective weed control.
 

How turfgrass tolerance can impact herbicide efficacy:

Selectivity:

Selective herbicides control specific weed species while minimizing damage to desirable turfgrass. Take for example the selectivity of the sulfonylurea herbicides vs warm season turf. This selectivity enables you to use many of these to remove turf type ryegrass from oversown sports grounds when you transition back to couch in the spring.

Safety margin:

Herbicide labels often provide specific application rates for different turfgrass species or cultivars. These rates are a direct result of turfgrass tolerance and are the range of herbicide rates that will not cause turfgrass injury.

Recovery and regrowth:

Tolerant turfgrass has the ability to recover after herbicide application. Even if some injury occurs, tolerant turfgrass recovers and resumes normal growth.

Herbicide options:

Turfgrass tolerance to herbicides affects what you can use. Certain turfgrass species or cultivars may have higher tolerance to specific herbicides, allowing for more effective control of target weeds without causing significant damage to the turf. Understanding the tolerance of your turfgrass to different herbicides can help in selecting the most appropriate herbicide for your specific weed control needs. Examples of this are:

  • Bispiribac sodium. There is a big difference between turf type perennial ryegrass cultivars.
  • Oxadiazon. You can’t use this on Santa Anna couch but It is safe on all other hybrid couch varieties.

Herbicide Formulation

There are several different turf and lawn herbicide formulations that you can use. These include liquid concentrates, dry granules, or ready-to-use sprays and the herbicide formulation you use directly and indirectly affects lawn and turf herbicide performance.
 
 
For example, liquids are typically more easily absorbed by plants.This means they give faster and more effective control. Granular herbicide formulations may require soil moisture for activation.
 
  • A good example of this is Onset 10GR a pre emergent granule herbicide formulation of prodiamine and the liquid herbicide formulation called Barricade herbicide.

Planning ahead

 
You should always try to plan ahead and be aware of what might be happen in the future. For example, there is no point in using a long term pre emergent turf or lawn herbicides like Specticle if you intend to overseed in two months.
 
Likewise plan for the worst case scenario. If you’re transitioning out ryegrass from couch think carefully before you decide on what to use for chemical transition. If problems do occur then using a chemical with a long reseeding period isn’t going to be the smartest decision you can make.

FAQ

When should I apply my lawn pre emergent?

The best time to apply these products is in the early spring as this is before broadleaf weeds begin to grow. For grass weeds like summer grass apply later say in late spring or early summer. This weeds germinate later, so by applying your pre emergent later you will get longer control.

What is a turf herbicide?

Turf herbicides, also known as weedkillers are pesticides used to control and manage undesirable plants. It is important that when you use a turf herbicide that you precisely follow the label directions. If you don’t do this then the herbicide may fail to control the target weed, damage the turf grass or even prevent you from being able to reseed or re-turf damaged areas.

Turf herbicides can be:

  • Selective or non selective. Selective turf herbicides are able to specifically target the weed without damaging the desirable turf grass. Non selective turf herbicides kill everything.
  • Pre emergent or post emergent. Pre emergent turf herbicides prevent weeds from growing and becoming and are used before weeds grow. Post emergent kill weeds after they have emerged.
  • Work against broadleaf weeds or grass weeds.

 

References

  • 1
    Kudsk, P.; Kristensen, J. Effect of environmental factors on herbicide performance. In Proceedings of the First International Weed Control Congress, Melbourne, Australia, 17–21 February 1992; Weed Science Society of Victoria: Victoria, Australia, 1992; pp. 173–186
  • 2
    Matzenbacher, F.O.; Vidal, R.A.; Merotto, A.; Trezzi, M.M. Environmental and physiological factors that affect the efficacy of herbicides that inhibit the enzyme protoporphyrinogen oxidase: A literature review. Planta Daninha 2014, 32, 457–463.
Senior Turf Agronomist at Gilba Solutions Pty Ltd | Website | + posts

After Graduating from Newcastle University with an Hons Degree in Soil Science in 1988, Jerry then worked for the Sports Turf Research Institute (STRI) before emigrating to Australia in 1993.

He followed this by gaining a Grad Dip in Business Managment from UTS and has worked in a number of managment roles for companies as diverse as Samsung Australia, Arthur Yates and Paton Fertilizers.

He has always had a strong affinity with the Australian sports turf industry and as a result he established Gilba Solutions in 1993. Jerry has written over 100 articles and two books on a wide range of topics such as Turf Pesticides and Nutrition which have been published in Australia and overseas.