A key tool for Turf Managers is to use Insecticides to prevent or minimise insect damage to Turfgrass. The key to the continued use of these is insecticide resistance management. Resistance management involves not using products with the same mode of action.

Globally there are over 20 different insecticide modes of action (MOA’s). Several of these are currently in use in Australia in the turf industry.

If you continue to use insecticides from the same chemical group, and which have the same mode of action it:

Pest species have a greater risk of resistance developing to that chemical group.
Means the risk of cross-resistance to other groups increases.

Cross Resistance to Turf Insecticides.

A good example of cross resistance that relates to turf is the Argentine Stem Weevil.¹ Research shows that if stem weevil larvae are resistant to bifenthrin, it results in a reduction in the efficacy of cyantraniliprole (found in Spinner insecticide), indoxacarb (Provaunt) and clothianidin.

Resistance even develops in products where you might think there will not be any issues. Take chlorantraniliprole (Acelepryn). In agriculture in 2023/2024 no resistance was seen in the cotton bollworm or corn ear-worm. However, in previous years resistance has been seen to this chemical.

Helicoverpa insecticide resistance to chlorantraniliprole (Acelepryn)

If you use chemicals that have different modes of action, this slows down the chances of pest species developing insecticide resistance. If you adopt this approach to resistance management in conjunction with certain cultural practices it is a good first step to slow down this entire process.

Cultural Practices to Prevent Insecticide Resistance.

The use of cultural practices to control an insect pest reduces the selection pressure from insecticides. Cultural controls include:

The use of high endophyte sports turf seed varieties like A-listed perennial ryegrass. These are research proven to have better resistance to insect attack due to their high endophyte levels. An example of this is, Intense PRG.
Ensure that your turf surface is in the best possible condition. This means mow at the right height, don’t overwater, and fertilise appropriately.
Monitor insect threshold levels. If pest numbers are below acceptable thresholds then don’t spray an insecticide.

Soapy Water Test.

If you plan to monitor pest numbers the soapy water test is a good way to allow you to count insect numbers in the soil. The soap irritates army worms, adult billbugs, or mole crickets and the result is that they come to the soil surface.

Soapy Water Recipe.

In 8 L of water add 30 ml lemon scented washing up liquid.
Apply this mix in a watering can to one square metre of turf.
Repeat every 14 – 21 days and count how many pests emerge after each treatment.

The other options is to use a Degree Day Model. All degree day models rely on the association between heat and insect development. These models can help better target insecticide applications so that you spray when they are at their most vulnerable.

Degree Day Models.

A good example is the use of a model to target the Argentine stem weevil ((Listronotus bonariensis). The stem weevil life cycle is temperature-dependent. This means that the warmer the temperature the faster its development and the shorter the intervals between each generation.

Here’s how it works:

Determine the Base Temperature. For Argentine Stem Weevil use 10°C.
Establish a Start Date. This very much depends on your location. For example, Canberra is colder than Sydney. This means that the start date in Canberra is going to be later than in Sydney
Track the daily temperature. Calculate the daily mean temperature (the average of the max + min).
Then subtract the base temperature (10) to give the daily degree days.
Keep a running total of the Degree Days. You can do this if you add up the daily degree days from the start date until the current date.
Compare the running total to the action thresholds for the different stem weevil life stages.
Use the right insecticide to target the life stage when the running total of degree days fall inline with the action thresholds.

Action Thresholds for Stem Weevil.

Adult Peak Migration: 110-120 GDD.
Eggs/Small Internal-Feeding Larvae: ~ 175 GDD.
Larvae Emerging from Stems: ~ 350 GDD.

Understand an insect or mite life cycle.

It’s vital to understand the life cycle of a turfgrass pest. If you do this you are able to better target your control methods. In a resistance program you will get the best results from any insecticide or miticide if you target pests when they are at their most vulnerable.

The control spectrum of a product is also important. Many current products, are active against more than one pest, and provide several benefits from one application.

Reduces the Development of Resistance.

When you expose an insect population to an insecticide which has only a single mode of action, individuals may survive and then reproduce. Over time these resistant individuals will tend to dominate the population.

If you use products that have more than one mode of action, you introduce different selection pressures. This makes it more difficult for any resistance to develop.

Improved Control.

With the use of different chemical groups you can target different insect life stages or behaviour. This means you are able to target for example larvae or adults.

You Get Better Control.

You can create a synergy between actives when you combine insecticides with different modes of action.

Less Chemical Use.

If you mix lower doses of chemicals than if you use them alone, it means there is less of an impact on the environment.

A good example of this approach is ProForce Scarlet Trio. One application controls African Black beetle, mites, argentine stem weevil, mole crickets, cutworms, armyworms and sod webworms.

How to Get the Best Results from an Insecticide.

To get the best results from an insecticide you need to accurately place the chemical where your target pest is. This affects the choice of formulation, your timing, how you apply it, and whether you need to water it in or not.

Insecticide Resistance Management Strategies.

A good insecticide resistance management strategy can give better results for a lower cost. For example, if a pest population is in surface thatch, then irrigate an hour before you spray as this draws insects to the surface. It also helps the chemical move better into the soil.

You can then follow up this with an appropriate amount of water or let rainfall wash it in.

If you don’t do this you will get at best mixed results. The majority of the chemical is likely to become trapped in the surface thatch and never reach its target.

Reasons for Insecticide Failure.

Factors such as volatilisation, not enough water, water repellant surface thatch and insect resistance can all have a negative impact on the results you get.

What is a Target Site?

Where an insecticide binds and works, is known as its target site.
Insecticide molecules are much smaller than the target protein molecules they work on.
The target proteins can have multiple sites where similar insecticides can bind.
How an insecticide interacts with the target site defines its mode of action.

How Mode of Action Helps Manage Insecticide Resistance.

Insecticides can have very different chemical structures but bind at the same target site. This means that they can have the same mode of action.

If you vary the insecticide group, it is an important tool to ensure that you can continue to control pest populations with these chemicals.

If you don’t “rotate” between different modes of action, and continue to use the same ones repeatedly, it just contributes to insecticide resistance. So look at newer options like Tetrino Insecticide as an alternative as this targets pests in several ways.

If you fail to do this it and just continue to use the same chemical groups it will just kills susceptible insects. This then leaves behind those with resistance to that entire insecticide class.

A rotation strategy that uses different chemical groups, is a good resistance management strategy. This approach slows down and helps prevent the development of resistance.

If you click on the image below you can get your free insecticide resistance management chart. Simply rotate between the MOA groups when you target your pests.

Rotating MOA groups will prevent insecticide resistance developing

References

1
Koppenhöfer AM, Kostromytska OS, Wu S. Pyrethroid-Resistance Level Affects Performance of Larvicides and Adulticides From Different Insecticide Classes in Populations of Listronotus maculicollis (Coleoptera: Curculionidae). J Econ Entomol. 2018 Aug 3;111(4):1851-1859. doi: 10.1093/jee/toy142. PMID: 29800225.

Jerry Spencer

Senior Turf Agronomist at Gilba Solutions Pty Ltd | 0499975819 | [email protected] | Website | + posts

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

He followed this by gaining a Grad Dip in Business Management from UTS. He has worked in a number of management 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 as an independent sports turf consultancy 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.

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Insecticide Resistance in Turfgrass.