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Thrips Resources

Thrips are one of the most difficult insects for flower growers to control.
For wholesale and retail florists, the damage from Thrips renders flowers unmarketable. 

Research on control of Thrips has been ongoing for many years, based primarily on the use of pesticides. Thrips are so small that the untrained eye rarely sees the insect, but the damage is apparent on infested flowers. Proper rotation of insecticides is critical to successful control. 

Thrips are known to develop resistance to insecticides very rapidly. Over the last 30+ years, Thrips control measures have been successful, to some extent, due to the introduction of new classes of insecticides and research showing the proper rotation of pesticides and cultural practices affecting Thrips.  

The industry is seeing fewer and fewer new insecticide classes introduced to the market, so Thrips seem to be developing a greater resistance to existing insecticides. In the past, there have been researchers focusing on pesticide control and others concentrating on biological control measures. In most cases, research has not looked at how best to use insecticides in unison so that specific recommendations could be developed for the industry.

Find more resources and solutions by clicking the topics below or watch webinars on top issues facing growers by clicking on the image below!

Topics Index:

Scouting
Management
Insecticide Info
IPM
BioControl
Cutting Dips
Marigolds as Guardian Plants
UV Light for Thrips Management
Hyperspectral Imaging
Manipulating Nutrient Inputs
Calcium Sprays for Thrips Control


Scouting

Key Takeaways:

  • Scouting is the most important part of a management program for thrips. Every grower, large or small, should develop a regular scouting program that is tailored to their specific needs and limitations.
  • Thrips populations typically follow annual cycles, staying low during short, cool days and increasing with longer, sunnier days and higher temperatures due to faster lifecycle completion.
  • In regions like South America, where day length is fairly constant, other external environmental factors can affect pest populations. Scouting and observation can help growers anticipate these influences.
  • Maintaining yearly records of thrips populations can help growers predict when to intensify pest control measures.
  • It’s beneficial to track common thrips occurrence locations (e.g., around vents or doors) and preferred plant species/varieties to identify infestation hotspots early.
  • Early identification of infestation hotspots allows for proactive, targeted insecticide sprays or natural enemy releases, rather than treating the entire greenhouse, which saves money and protects the environment and beneficial insect populations.

Resources:

Recursos en Español:


Management

Key Takeaways:

  • Thrips are difficult to manage for a number of reasons:
    • They are very small, making them hard to find. 
    • The host range spans over 500 plant species.  
    • Females lay about 7 eggs per day, are parthenogenic (meaning females can produce offspring with or without males) and can easily produce over 200 offspring in a month. 
    • Young thrips mature quickly and can reproduce in 9 to 13 days at temperatures around 77 to 86°F (25 to 30°C), thus a population can go from 1 to 6,000 thrips in about 42 days. 
    • Thrips can be resistant, and can quickly develop resistance, to commonly used insecticides. There are at least 175 documented cases of insecticide resistance in western flower thrips from around the world, involving at least 8 different mode of action groups. 
  • Careful consideration of these factors is needed before management decisions can be made.

Resources in English:

Recursos en Español:

Webinars:

Seminarios Web:


Insecticide Info

Key Takeaways:

  • Western Flower thrips develop insecticide resistance quickly.
  • Insecticides don’t protect flowers for a long time and are limited to flowers that are open at the time of application. Repeated spray applications are required to protect flowers through the production cycle.
  • Use insecticides only when necessary to prevent resistance.
  • Rotate insecticides among different modes of action or IRAC group numbers
  • Combine cultural, biological, and chemical control measures for best results
  • There is no one-size-fits-all program. Every operation will be different.

Resources:

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Webinars

Seminarios Web:


IPM

Key Takeaways:

  • At the basis of every IPM program is the right plant, ideally resistant or not susceptible to pests, not stressed, and not over-fertilized. Here are some tips to start an IPM program for Thrips:
  • Start with clean facilities by sanitizing the floors and benches before production, removing weeds under benches and around from the growing area, and eliminate infested plant material.
  • Inspect incoming plant material before bringing it into the production area, and discard it if it is infested.
  • Use a preplant cutting dip (see Cutting Dips section for more info), such as an insect-killing fungus to target pests coming in on propagation material.
  • Establish flowering, potted marigold plants where thrips are likely to occur, such as near vents and doors. Yellow marigolds have been shown to be effective as a guardian plant (see Marigolds as Guardian Plants)
  • Establish a regular scouting program for the production area that includes recording the the findings, and refer to it frequently before considering a treatment.
  • Identify pest hot spots early and target them with a spot spray or release of natural enemies, rather than making applications over the entire production area.
  • Rotate pesticides properly, considering the mode of action, to avoid creating pesticide resistant pest populations.

The following sections on this page include strategies that can be implemented into an IPM program for Thrips.


BioControl

Insect-Killing Fungi

Key Takeaways

  • Beauveria bassiana is an insect-killing fungi that will kill thrips
  • Preventative and curative applications are effective for thrips control
  • When applying as a cutting dip, good coverage is essential.
  • When spraying, use a low volume, fine mist that contacts both the top and underside of the leaves. Avoid run-off.
  • Cold fogging is possible to apply insect-killing fungi like Beauveria bassiana
  • Granular formulation applied on the growing media helps control thrips pupae
  • Beauveria bassiana can be applied in the soil of guardian plants such as yellow marigolds to kill thrips pupae (see Marigolds as Guardian Plants)

Predatory Insects

Key Takeaways

  • There are many native and naturally occurring landscape predators that are the same or similar to commercially available biocontrol agents in the US, such as lacewings, hover flies, or lady bugs.
  • Many predatory insects can be mass reared on the farm or attracted to habitat plants.
  • Regular releases of predators will prevent and reduce thrips populations.
  • Mineral oils are very useful to combine with biocontrol (i.e. as a cutting dip) but are not technically a biopesticide.
  • Azatin O 4.5 (a biological insect growth regulator) and BotaniGard (Beauveria bassiana strain GHA) are shown to be effective at killing thrips without adversely affecting natural predators such as leaf miners and Amblyseius swirskii (a predatory mite).

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Webinars:

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Cutting Dips

Key Takeaways:

  • Good sanitation is essential.
  • Risk of disease (i.e. Erwinia/Pectobacterium) transfer is minimal, but don’t dip stressed cuttings since they may be more susceptible to pathogens.
  • Dip rates are lower than spray rates to prevent phytotoxicity.
  • Do your own tests on a small batch before committing to a full dip program.
  • Optimum results for thrips were obtained with 0.1-0.5% (v/v) mineral oil (e.g. Landscape oil or SuffOil-X) or 2.5 g/L BotaniGard 22WP on various crops. Adjust the rate according to the sensitivity of the crop to oil-based products.
  • Products used in dips work on contact with pests, so total coverage of the foliage is required. Do not pack the cuttings too tightly and check for dry spots after the cuttings are dipped.

Resources:

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Videos:


Marigolds as Guardian Plants

Key Takeaways:

  • Yellow marigolds are very attractive to western flower thrips.
  • They are ideal guardian plants because they are easy to grow and bloom within 1 month. 
  • Thrips are often found 2 weeks earlier on marigolds than on yellow sticky cards.
  • Marigolds can lure thrips out of the crop plants, where they can be managed with various biological control agents. If thrips populations can be reduced early in the season, they may not become a serious problem later.

How it Works:

  • The guardian plant strategy uses an Attract, Sustain, and Kill approach.
  • Flowering marigolds attract thrips out of the crop. A slow-release sachet containing predatory mites (Neoseiulus cucumeris) is attached to the marigold to attack thrips adults and immatures on the foliage.
  • A millet-based granular formulation of Beauveria bassiana (the isolate in BotaniGard® products) can be mixed into the top layer of potting soil to control thrips pupae for a period of at least 12 weeks. This fungus grows in the soil and creates a fungal mat that infects the immature thrips as they descend to pupate.
  • The key to success is to get the flowering marigolds into the crop early, before thrips populations begin to build. Growers must be proactive when using biological control and guardian plants are an easy low-cost way to start early.
  • Guardian plants should be placed every 1,000 sq. ft., raised a few inches above the crop. To be effective, they must be introduced early before thrips populations begin to build. They provide prolonged thrips suppression for at least 2-3 months and are a low-cost pest management solution.

Guardian Hedges:

  • In warmer climates, where there is a constant source of thrips from outside, the guardian plant concept could be extended to incorporate plant hedges around the greenhouse. These plant hedges contain a variety of annuals that attract thrips, beneficial insects, and pollinators.
  • Habitat hedges should be regularly monitored for thrips populations. If damaging levels are detected, targeted chemical treatment can be applied.

Resources:

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Webinars:

Seminarios Web:


UV Light for Thrips Management

Key Takeaways:

  • Preliminary results indicate that exposure to UV light impacts the survival and behavior of thrips adults and larvae, with adults showing more resistance.
  • Adult thrips showed a slower mortality rate compared to larvae when exposed to UV light.
  • UV-C light applied to plants from top-mounted lamps does NOT expose all thrips. Most thrips are located on the underside of leaves, so light needs to target the underside.
  • The highest test dose of UV light led to the death of half of the adult thrips 48 hours after exposure.
  • Thrips larvae were generally more susceptible to UV light exposure compared to adults. Their mortality rate increased over time, peaking after 120 hours in all dosages.
  • The findings suggest that UV light can be a useful tool in controlling WFT populations, but the effect is dosage and time dependent and differs between adults and larvae.
  • UV-C light may cause changes in the plant that make them less attractive to thrips.
    • This study is still underway – stay tuned for more results!

Resources:

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Hyperspectral Imaging

Key Takeaways

  • Healthy, non-infested plants have uniquely different leaf reflectance compared to those with pest infestations.
  • The researchers identified 19 spectral bands that were used to develop a classification algorithm, achieving an overall accuracy of about 74% in detecting thrips infested plants.
  • The study demonstrates the ability to detect subtle thrips infestations with high accuracy using the custom-built imaging system.
  • The researchers invite collaboration from ornamental growers to further validate the classification algorithm and test the machine vision system in commercial greenhouse settings.
  • Stay tuned for more information from this project!

Resources:

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Manipulating Nutrient Inputs

Key Takeaways

  • Organic nitrogen is an important element for insect nutrition.
  • By manipulating the amount and type of fertilizer we give to the crop, we can change the plants’ nutritional value for pest insects.
  • Current research indicates that many production guides may be recommending more nitrogen than is needed.
  • Thrips laid more eggs on plants grown with 250 ppm N than 75 ppm N.
  • This study showed a possible reduction of thrips on potted chrysanthemum with low rates of fertilizer, but plant quality was affected.
  • However, a metabolite known to be involved in thrips resistance was higher in plants with low fertilizer treatments.
  • Results indicate that plants grown at lower fertilizer rates are less suitable host plants for thrips due to:
    • Lower concentrations of amino acids (= less food)
    • Higher concentrations of chlorogenic acid (= increased defenses)
    • Increased jasmonic acid induction from thrips feeding (= increased defenses)

Resources:

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Calcium Sprays for Thrips Control

Key Takeaways:

  • Sprays of calcium chloride and potassium silicate did not reduce thrips abundance and damage on petunia, daisy, and rose flower petals.

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To see resources for treating Botrytis, click here.