NZPPS pesticide resistance management strategy (2023)

NZPPS pesticide resistance management strategy (1)
Some NZ populations of fathen
Chenopodium album are resistant
to triazine herbicides.

K.C. Harrington1 and T. James2
1Massey University, Private Bag 11-222, Palmerston North, New Zealand
2AgResearch, Ruakura Research Centre, Private Bag 3123, Hamilton, New Zealand

(Revised September 2020)


Most maize crops in New Zealand that are harvested for grain are grown as a non-rotational monoculture. The ground is usually left fallow between maize crops and on some cropping farms maize has been grown continuously for well over 40 years. This is a classic scenario for development of herbicide resistance. The best way to avoid herbicide resistance in continuous monoculture is to rotate the herbicides used for weed control ensuring that herbicides with differing modes of action (see Table 1 below) are routinely used in successive crops.

However, in the early years of maize cropping there were less herbicides to rely on and atrazine was regularly used every year for control of broadleaf weeds. Thus it was hardly surprising that the first case of herbicide resistance in New Zealand was discovered in maize paddocks. The weed fathen (Chenopodium album) developed resistance to atrazine in the early 1980s and is now widespread on cropping farms. In the 1990s both willow weed (Persicaria persicaria formally Polygonum persicaria) and black nightshade (Solanum nigrum) also developed resistance to atrazine although these biotypes are fortunately not so widespread (Rahman & Patterson 1987; Harrington et al. 2001).

When fathen developed resistance to atrazine, alternative herbicides were immediately found to control it. However, some of the alternative herbicides were relatively expensive and/or had narrow weed spectrums. With dicamba, maize growers found a herbicide that was not only cheap but also controlled a wider range of difficult to control weeds, such as Californian thistle (Cirsium arvense) and pink bindweed (Calystegia sepium). Unfortunately, because of this practice dicamba has been used repeatedly, and dicamba resistance has also developed within fathen in some areas of Waikato (James et al. 2005). Thus there is now a biotype of fathen that is resistant to atrazine only and another biotype that is resistant to both atrazine and dicamba.

Further cases of herbicide resistance are starting to appear in places. For example, summer grass now appears to be developing resistance to nicosulfuron on a few farms growing maize.

Resistance management and prevention strategy

Strategies for dealing with herbicide-resistant fathen and willow weed in maize crops have been published in the past (Harrington & James 2005) and are updated here. One way to overcome these problems is to not grow maize in the same paddock for too many years in succession, but rather, to rotate maize with other types of crops or pasture. This will at least slow the rate at which resistant weeds will build up.

A more practical strategy for some farmers involves the choice of herbicides. By applying a combination of two or even three herbicides, each with different modes of action, weed plants resistant to one of the herbicides will be controlled by another herbicide and so be unable to set seed and multiply within a paddock. When rotating herbicides, it is important to understand that some herbicides are very similar in their chemical structure and action (Table 1). Rotating between herbicides within the same chemical group serves no useful purpose because a weed that is resistant to one member of a group will usually be resistant to all other members of that group.

Table 1:Herbicides suitable for use in maize. To avoid resistance developing, alternate with herbicides from different chemical groups.
Chemical groupActive ingredientProducts

ALS Inhibitor (B)


eg Preside, Aim, Blast, Valdo




eg Latro, Neeko Oleo, Adapt, Corvette

Triazine (C1)


eg Atraflo, Atratec, Nu-trazine


Bladex, Bruno, Cytec


eg Terbaflo, Terb 500, Asset, Magneto

Triazinone (C1)


eg Sencor, Jazz, Metriphar, Charger

Substituted Urea (C2)


eg Afalon, Linuron 50 DF, Linex Flo

Nitrile (C3)


Emblem Flo, Bromotril

Pyrimidinedione (E)



Triketone (F2)



eg Mesoflex, Primiera, Dominator


Dinitroaniline (K1)


Stomp Xtra, Strada, Agpro Pendimethalin

Chloroacetamide (K3)


eg Roustabout, Sylon, Joker, MaizeGuard


eg Corral, Alaken, Taipan Encaps




Metoken Gold



Benzoic (O2)


eg Cutlass, Kamba, Bandit, Performa

Pyridine (O3)


eg Versatill Powerflo, Archer, Multiple

Weed control in maize crops normally includes the use of triazine herbicides. These control many broadleaf and some grass weeds, but they are weak on many grasses, such as smooth witchgrass (Panicum dichotomiflorum) and barnyard grass (Echinochloa crus-galli). Therefore a second herbicide is usually also applied. Herbicides that control most grasses and so are suitable to add with a triazine include the chloroacetamides and pendimethalin. More recently a range of herbicides has become available that can be applied post-emergence. Some are specific and control only broadleaf weeds while others control both grass and broadleaf weeds. These are also good tools for managing herbicide resistance.

To prevent herbicide resistance to the triazines from building up, either the triazine herbicide should be completely spelled for a season and another class of herbicides used to control the broadleaf weeds such as mesotrione or a second carefully selected herbicide should be used in conjunction with the triazine to control problem species.

Most of the post-emergence herbicides currently available will control resistant weeds. Dicamba is the most widely used for control of atrazine-resistant fathen. However, over use of this herbicide has led to dicamba resistance. Dicamba should not be used repeatedly but should be rotated with other suitable post-emergence herbicides. Fortunately, the dicamba-resistant biotype of fathen is not cross resistant to other herbicides (with different modes of action) so in the short term this weed can be controlled with these other post-emergence herbicides, such as nicosulfuron, bromoxynil and mesotrione. Of major concern is the over-use of these post-emergence herbicides.

One of these herbicides is nicosulfuron, belonging to a chemical family (ALS inhibitors) that has shown great predisposition to herbicide resistance. In fact more weeds have developed resistance to this herbicide group, and in a shorter time, than to any other herbicide group (Heap 2020). Therefore, when controlling fathen (either atrazine-resistant, dicamba-resistant or non-resistant) repeated use of any one herbicide must be avoided and longer term rotations should be employed. Some resistance to nicosulfuron has been found to have developed in summer grass, so rotating use of nicosulfuron with pre-emergence applications of acetochlor, or post-emergence applications of topramezone, would help with managing this risk. Another option, rather than using rotation, is to apply mixtures, such as nicosulfuron with mesotrione at post-emergence.

Although not widely used for weed control in maize, metribuzin and linuron are registered for this purpose but note that metribuzin is closely related in structure to the triazines, so alternating between triazines and metribuzin would probably not prevent resistance from building up. Some atrazine-resistant fathen biotypes overseas are also resistant to metribuzin.

When a new case of herbicide resistance appears in a maize paddock, such as summer grass resistant to nicosulfuron, there is also a range of cultural strategies that should be considered to prevent spread of the resistant weeds. In particular, harvesting machinery and cultivators should be cleaned after working in a paddock where new cases of resistance have appeared, to reduce the chances of resistant weed seeds being transported to other paddocks and farms free of resistance. The weed species should also be controlled around the fence-lines and field boundaries using a combination of knockdown and residual herbicides, or growing a suppressive species such clover in the case of summer grass then controlling grass weeds with a selective herbicide.


The assistance of colleagues in initially devising this strategy in 1994 is gratefully acknowledged, especially Graeme Bourdôt, Anis Rahman, Trevor Patterson, Roger Field, Mike Cornwell, Bob Moffatt and Murray Willocks. More recently, assistance from Mike Parker has been appreciated.


Harrington KC, James TK 2005. Managing herbicide resistance in maize. In: Martin NA, Beresford RM, Harrington KC ed. Pesticide resistance: prevention and management strategies 2005. New Zealand Plant Protection Society, Hastings, New Zealand. Pp. 147-150.

Harrington KC, Ward AJ, Wells DM 2001. Herbicide resistance in black nightshade and Onehunga weed. New Zealand Plant Protection 54: 152-156.

Heap I 2020. International herbicide-resistant weed database. (15/9/20).

James TK, Rahman A, Mellsop JM 2005. Fathen (Chenopodium album): a biotype resistant to dicamba. New Zealand Plant Protection 58: 152-156.

Rahman A, James TK, Mortimer J 1987. Control of atrazine-resistant fathen in maize. Proceedings 36th New Zealand Weed and Pest Control Conference: 229-232.

Rahman A, Patterson TM 1987. Polygonum persicaria: A triazine-resistant biotype. Proceedings 40th New Zealand Weed and Pest Control Conference: 186-188.


What are some strategies to reduce pesticide resistance? ›

Managing Pesticide Resistance
  • Minimize Pesticide Use. Minimizing pesticide use is fundamental to pesticide resistance management. ...
  • Avoid Tank Mixes. Avoid combinations (mixes) of two insecticides or miticides in a single application. ...
  • Avoid Persistent Chemicals. ...
  • Use Long-term Rotations.

What is the best explanation of how pesticide resistance can arise? ›

Genetics and intensive application of insecticides are responsible for the rapid development of resistance in many insects and mites. Selection by an insecticide allows some insects with resistance genes to survive and pass the resistance trait on to their offspring.

What is one important strategy for reducing the use of pesticides? ›

Try using non-chemical management methods on your lawn and garden, such as introducing beneficial insects and wild, native plants, or use physical methods, including hand weeding, mulching, or setting traps, to reduce chemical use outdoors.

How a farmer gets on the pesticide treadmill? ›

Also referred to as the "pesticide trap," farmers get caught on the treadmill as they are forced to use more and more — and increasingly toxic — chemicals to control insects and weeds that develop resistance to pesticides.

What are two methods we can use to reduce the possibility of resistance to herbicides? ›

Placing fertilizer closer to the seed and using insect and disease protection when necessary will also improve crop competitiveness. Later seeding dates allow control of early weeds in the pre-seed window. Tillage and spot mowing to prevent seed set are mechanical alternatives.

What are 5 ways that you can reduce exposure to pesticides? ›

  • Use non-pesticide methods.
  • Don't apply more than needed.
  • Read product label.
  • Follow product label instructions.
  • Keep pesticides away from kids and pets.

What is an example of pesticide resistance? ›

Some plant pathogens have also become resistant to pesticides. Among fruit producers in North America, apple growers perhaps have faced the most significant problems with pesticide resistance. Examples include streptomycin resistance in the fire blight bacterium and benomyl resistance in the apple scab pathogen.

What are three ways we can slow down or stop resistance in bacteria and pests? ›

Infection-prevention activities have been proven to be effective in slowing the spread of resistant germs. These include vaccination, implementing hand hygiene and responding rapidly to unusual genes and germs when they first appear.

Which statement best describes how only a few resistant individuals resulted in the pesticide becoming ineffective? ›

Some individual insects have a genetic mutation that makes them resistant to the toxins in the pesticides. Which statement best describes how only a few resistant individuals resulted in the pesticide becoming ineffective? F The resistant insects change the toxin on the plants, making it safe for others.

How would you know if the pest is becoming resistant to a pesticide? ›

When the pesticide applicator recognizes that the once-highly-effective pesticide no longer controls the pest at the same rate, higher rates and more frequent applications become necessary until eventually, the pesticide provides little or no control. The population may then be said to have become resistant.

What are the 4 main modes of action of pesticides? ›

Insecticides Used in the Urban Environment: Mode of Action
  • Insecticides that Affect the Nervous System. ...
  • Insecticides that Inhibit Energy Production. ...
  • Insecticides that Affect the Insect Endocrine System. ...
  • Insecticides that Inhibit Cuticle Production. ...
  • Insecticides Affecting Water Balance.

What are the 4 methods of integrated pest management? ›

Pest management methods fall into four groups: cultural, mechanical, biological, and chemical.

What are the 3 major problems of pesticides? ›

Pesticides can contaminate soil, water, turf, and other vegetation. In addition to killing insects or weeds, pesticides can be toxic to a host of other organisms including birds, fish, beneficial insects, and non-target plants.

What is the most commonly used pesticide today? ›

Glyphosate, also known by the trade name Roundup, is the most widely used herbicide in the United States.

How can farmers get rid of pests without using pesticides? ›

Use Mechanical Control Techniques to Manage Pests

Use crop cultivation and shallow tillage operations to control weed seedlings. Pull weeds by hand or use a hoe for smaller, additional, weed infestations. (Don't let them gain a foothold.)

What is the most important strategy for managing herbicide resistance? ›

Do not let resistant weeds go to seed. Avoid moving seed or vegetative propagules to other fields and farms. Use a power washer or compressed air to help remove seed and plant parts from any equipment used in the field. If any fields have a history of herbicide-resistant weeds, use farm equipment in those fields last.

What are the top three strategies used to control established noxious weeds? ›

The top three strategies used to control established noxious weeds were chemical control, grazing, and biological control. Nearly half of respondents utilized integrated weed management, which is management that uses more than one control strategy.

Which herbicide group has the most resistance? ›

The greatest number of resistant biotypes worldwide has been observed with the ALS inhibitors (imidazolinones, pyrimidinylthiobenzoates, sulfonylureas, triazolopyrimidines). The second most common group with resistant biotypes is the photosystem II inhibitors (primarily triazines).

Does soaking fruit in salt remove pesticides? ›

Give it a Saltwater Soak

Research suggests that soaking fruits and vegetables in a 10 percent saltwater solution for 20 minutes gets rid of most of the residues from the four most common pesticides.

Does mopping remove pesticides? ›

Yes, mopping and cleaning will remove pesticides unless they've been applied to a particularly porous surface.

What will neutralize pesticides? ›

Researchers discovered that 10% salt water solution is effective for removing common pesticide residues including DDT. Rinse with water afterwards. Use bicarbonate of soda(also known as bicarb and baking soda) to clean your fruits and vegetables. Add 1 teaspoon of bicarb to 2 cups of water and soak for 15 minutes.

What are 4 insects that have a chemical resistance to pesticides? ›

Discussion. Species that have developed resistance to most insecticides used against them include the cotton leafworm, Spodoptera littoralis, in Egypt; the cattle tick, Boophilus microplus, in Australia; the housefly Musca domestica; and many species of Anopheles mosquitoes worldwide (Forgash 1984, Georghiou 1986).

Why is pesticide resistance a major concern? ›

Over time many pesticides have gradually lost their effectiveness because pests have developed resistance – a significant decrease in sensitivity to a pesticide, which reduces the field performance of these pesticides.

How common is pesticide resistance? ›

Worldwide, more than 600 species of pests have developed some level of pesticide resistance.

What are the 3 ways you can control pest without harming the environment? ›

4 Eco-Friendly Pest Control Methods
  • Plant Your Pest Control in Your Garden. Mint, basil, lavender, rosemary and other herbs work really well as a natural pest control. ...
  • Season Your Window Sills. ...
  • Clean with Vinegar and Essential Oils. ...
  • Use Food Waste to Turn Pests Away. ...
  • Keep Pets Safe While Doing Pest Control.
Apr 9, 2019

What are the 3 most common superbugs? ›

Escherichia coli, Staphylococcus aureus and Klebsiella are the antibiotic-resistant pathogens most commonly associated with healthcare-associated infections, according to a study published in Infection Control and Hospital Epidemiology.

What are the three types of host plant resistance affecting the pests? ›

Crop varieties that are resistant to pest damage are said to have host plant resistance. Host plant resistance can be broken down into three categories: non-preference, antibiosis, and tolerance.

Which a population of insects become resistant to a pesticide? ›

In the natural environment the mutant insect is typically compromised, weaker and produces less progenies. Upon exposure to insecticides, insects that do not carry the resistance genes die, thus allowing the individuals with the resistance genes to survive and reproduce, creating more resistant insects.

What are the three things that can degrade a pesticide and reduce its persistence in the environment include choose all that apply? ›

Three types of pesticide degradation are microbial, chemical, and photodegradation. Microbial degradation is the breakdown of pesticides by fungi, bacteria, and other microorganisms that use pesticides as a food source.

What are the three steps by which a population of insects becomes resistant to a pesticide 22? ›

Step 1. Most pests die, only a small number survive; Step 2. Genes for resistance are passed on to the next generation; Step 3. Individuals with a resistant gene dominate the population and become insensitive to insecticide.

What is the main mechanism behind pesticide resistance? ›

Metabolic resistance is the most common mechanism and often presents the greatest challenge. Insects use their internal enzyme systems to break down insecticides. Resistant strains may possess higher levels or more efficient forms of these enzymes.

What are the mechanisms of pesticide resistance? ›

There are two basic resistance mechanisms existing in pests, i.e., target site resistance and metabolic resistance. During resistance of target site, the specific binding site of an insecticide is modified (mutated) and/or lost, which makes the target site incompatible for activation.

Is pesticide resistance increasing farmers in the US? ›

Pesticide resistance is increasing in occurrence. In the 1940s, farmers in the U.S. lost seven percent of their crops to pests, while since the 1980s, the percentage lost has increased to 13 percent, even though more pesticides are being used.

What are the three 3 routes of entry for pesticides? ›

The three main entry routes for these compounds into the body are dermal, (exposure through the skin or eyes), respiratory (inhalation into the lungs), and oral (ingestion by mouth).

What are the 3 basic methods of pesticide migration? ›

Moreover, pesticide contamination moves away from the target plants, resulting in environmental pollution. Pesticides move in several ways, including to the air, through wind currents, to water, through runoff or leaching, and to plants, animals, and humans [31,171].

What is the difference between a pesticide and an insecticide? ›

'Pesticide' is the general term for a chemical that kills pests. Pests can be weeds, insects, nuisance rodents, diseases, etc. An insecticide is a type of pesticide. Insecticides kill insects.

What are the six control method in pest management? ›

Most specific insect control methods can be classified into the following major categories: cultural control, host resistance, physical control, mechanical control, biological control, and chemical control.

What is the single most important component of a pest management program? ›

1. Pest Identification. Before deciding to take any pest control action, be sure you have correctly identified the pest (insect, mite, disease, weed, vertebrate, etc.). Proper pest identification is essential for determining if control is necessary and for selection of the best suited control options.

What are the 5 steps of integrated pest management? ›

Steps of Integrated Pest Management (IPM)
  • Proper identification of damage and responsible "pest" ...
  • Learn pest and host life cycle and biology. ...
  • Monitor or sample environment for pest population. ...
  • Establish action threshold (economic, health or aesthetic) ...
  • Choose appropriate combination of management tactics. ...
  • Evaluate results.
Jun 30, 2022

What are the most toxic types of pesticides? ›

  • Glyphosate (acid)
  • Glyphosate-diammonium.
  • Glyphosate-isopropylamine (also known as glyphosate–isopropyl ammonium; -IPA)
  • Glyphosate-monoammonium.
  • Glyphosate-sodium.
  • Glyphosate-trimesium.

What country doesn t use pesticides? ›

Bhutan plans to become the first country in the world to turn its agriculture completely organic, banning the sales of pesticides and herbicides and relying on its own animals and farm waste for fertilisers.

What are 5 common pesticides? ›

Examples of pesticides are fungicides, herbicides, and insecticides. Examples of specific synthetic chemical pesticides are glyphosate, Acephate, Deet, Propoxur, Metaldehyde, Boric Acid, Diazinon, Dursban, DDT, Malathion, etc.

What state uses the most pesticides? ›

California uses more pesticides than any other U.S. state, primarily because of the large acreage of high-value specialty crops: Almost 200 million pounds per year of pesticide active ingredients were applied to California farms in 2016, the most recent year for which data were available.

What is the number one pesticide in America? ›

The USDA also does not test fruits and vegetables for all pesticides used in crop production. For example, glyphosate is the most heavily used pesticide in the U.S., and it can be found in high levels on several grains and beans, such as oats and chickpeas.

What is the strongest pesticide? ›

In general, deltamethrin is considered one of the most powerful synthetic pyrethroid insecticides on the market.

How do I get rid of pesticides without killing my plants? ›

Rinsing: Rinsing produce in warm water for at least one minute or longer can help reduce pesticide presence on produce. Soaking: Soaking produce in warm water is one of the easiest and most effective ways to remove pesticide residues.

What strategies can do farmers take to control pests? ›

They till their soils, rotate their crops, scout their fields, and carefully consider factors such as plant density and planting dates. They also apply organic and synthetic pesticides.

What are 3 effective ways to reduce intake exposure to pesticides in foods? ›

Reducing our exposure to pesticides and other chemicals in food
  • Buy organic produce.
  • Thoroughly wash all fruit and vegetables (even organic).
  • Grow your own vegetables.
  • Peel vegetables or remove the outer layer of leaves.
  • Trim visible fat from meats – as many residues are fat soluble.
  • Cook meat and chicken thoroughly.

What steps can be taken to reduce or eliminate pesticide drift? ›

Ways to minimize or prevent pesticide drift:
  1. Adjust your nozzle(s) and pressure to make bigger droplets. ...
  2. Apply pesticides during calm weather conditions. ...
  3. Avoid applications when there is fog hanging in the air. ...
  4. Applying some herbicides before hot weather can lead to vapor drift.
Aug 23, 2022

What are the 3 different best ways to reduce pesticide residue intake from fruits and vegetables? ›

Wash your produce under running water rather than soaking or dunking it. Dry produce with a clean cloth towel or paper towel when possible. Scrub firm fruits and vegetables, like melons and root vegetables. Discard the outer layer of leafy vegetables, such as lettuce or cabbage.

Does peeling fruit remove pesticides? ›

A. Peeling foods with edible skins will probably remove additional pesticide residue, but not all. (Some pesticides are systemic, meaning they're absorbed through the plant's root system into the flesh and can't be washed off.)

What is one of the 3 basic rules of pest control? ›

IPM focuses on two parts – prevention and control – and has three basic rules: (1) Deny pests access to the establishment; (2) Deny pests food, water, and a place to hide or nest; and (3) Work in partnership with a PCO to eliminate any pest that does gain access to the establishment. Help!

What are the 3 principles of pest control? ›

Whenever you try to control a pest you will want to achieve one of these three goals. or some combination of them: prevention - keeping a pest from becoming a problem. suppression - reducing pest numbers or damage to an acceptable level, and . eradication - destroying an entire pest population.

What are three effective ways of managing insect pest populations? ›

Use of predators and parasites as biocontrol for pests are handled in one or more of 3 ways;
  • conservation and encouragement of naturally occurring biocontrol organisms by cultural techniques or at least avoidance of harming them.
  • augmentation of naturally occurring species by purchasing and releasing more of the same.
Mar 30, 2011

What two things should pesticide applicators be most aware of to avoid spray drift? ›

What two things should pesticide applicators be most aware of to avoid spray drift? Droplet size and wind direction and speed.

How much wind is too much for spraying weeds? ›

Always follow label information, although generally, wind speeds of 3 to 7 miles per hour (mph) are preferable. Spray at low wind velocities (less than 10 mph). If wind speed or direction changes during an application, immediately adjust the buffer size or location or stop the application.

What is the most effective way to remove pesticides? ›

Rinsing: Rinsing produce in warm water for at least one minute or longer can help reduce pesticide presence on produce. Soaking: Soaking produce in warm water is one of the easiest and most effective ways to remove pesticide residues.

Does vinegar remove pesticides from fruits and vegetables? ›

According to the experts from The Environmental Working Group, white vinegar comes with acetic acid, which can dissolve chemicals such as pesticides present on the skin of fruits and veggies. The acid can also kill about 98 percent of bacteria on your produce.

Can baking soda remove pesticides from vegetables? ›

Baking soda removes up to 96% of pesticides from fruit and vegetables. When mixed with water and gently rubbed on apple skins, the solution eliminates nearly all the reside left by two commonly-applied pesticides within 15 minutes.

How do you remove 100% pesticides from fruits and vegetables? ›

Hold the fruit or vegetable under flowing water in a strainer. This removes more pesticide than dunking the produce. The FDA does not recommend washing fruits and vegetables with soap, detergent, or commercial produce wash. They have not been proven to be any more effective than water alone.


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