New Chemical Control Option for Thrips and Whitefly

Thrips-tabaci-female-1-1024x683A new pesticide is available  for greenhouse ornamental production in Canada that has shown potential for effective suppression of difficult-to-control thrips and whitefly species.

But to keep this new tool effective, growers will have to use this chemical wisely. Keep reading for  efficacy data on ornamental crops and best management practices for incorporating this chemical into your IPM toolbox.

Ference – a New Registration for Thrips:

For several decades now, there have been few real chemical control options for Western flower thrips in Canadian floriculture, due to this pest’s overwhelming ability to become resistant to chemicals.  Further compounding this, the majority of our Western flower thrips populations in greenhouses come from imported cuttings, meaning they can arrive with resistance issues.  Chemicals that have given some control of thrips in recent years include DDVP (dichlorvos), Pylon (chlorfenapyr) and sometimes Success (spinosad). But, results vary highly between thrips populations at different farms and on different crops.

Additionally, ALL of the above options essentially wipe out thrips biocontrol programs, being hard on predatory mites (even in sachets). Their use means getting your thrips bio program up and running again can be difficult, and can often put you back on a pesticide “treadmill” for a crop cycle.

However, Ference (i.e. cyantraniliprole; known as Mainspring in the U.S. and Exirel for field crops in Canada), is considered soft on all predatory mites, according to Koppert’s pesticide side-effects database.  This makes it a better option for growers who rely on biocontrol to get occasional thrips outbreaks under control. (For details on Ference and it’s application, see the most up-to-date label from Health Canada here).

But does it work??? Although we can’t predict what kind of control Ference will provide across all thrips populations, a recent grower trial in cut chrysanthemums (outlined below) suggests it can be effective in certain cases.

Grower Case Study (Ontario): 

The Problem:  This grower started to see unusual and significant damage to the buds, blooms and some foliage of their cut mums in early February, despite having a robust mite-based biocontrol program.  Thrips numbers caught on monitoring cards were  higher than usual (Figure 1, below), and there was a lot more variation (difference) in thrips numbers between greenhouse sections (as indicated by the standard error bars in the graph).

cut mum damage flowers

Heavy feeding damage (white streaks) and distorted petals caused by thrips feeding at the bud stage on cut chrysanthemums. Foliar damage by thrips can also be seen in the background. Photo courtesy of A. Summerfield (UofG).

Sampling (plant taps) by OMAFRA and University of Guelph student Ashley Summerfield showed that the thrips population was a roughly split between Western flower thrips and onion thrips – a fairly new pest we’ve been seeing in Ontario greenhouses.  The presence of high numbers of onion thrips (especially in specific varieties such as “white magnum” and “feelin’ green”) helps explain why the grower’s usual biocontrol program wasn’t working. (See here and here for more information on onion thrips in ornamentals).

Western (left) onion (mid) chrysanthemum (left)

The efficacy of pesticides registered in Canada for thrips control is likely dependent on the species present in your greenhouse, and their source.  Thrips pictured here include western flower thrips (left), onion thrips (centre) and chrysanthemum thrips (right). Photo credit: A. Summerfield (UofG).

The Plan:  As mites, nematodes,  Beauveria applications and large amounts of mass trapping cards were not providing control, and the damage to the blooms was making many of the flowers unsellable, consultant Graeme Murphy (BioLogical Consulting) suggested quick action with pesticides was needed.

Ference efficacy

The Outcome:

The grower sprayed successive greenhouse rows until all mum varieties received 2 applications of Ference by mid- March.  Thrips numbers began to decrease after all zones received one application (Feb 22nd)Numbers returned to normal levels on the monitoring cards by early March – applications were continued for a period to ensure coverage and continued control.

Conclusions:

In this case, Ference appeared to suppressed all thrips (given the drop in total thrips on cards), with little effect on predatory mites. This allowed remaining mites in  sachets to get a foothold again, leading to a success story.

Because this grower had an infestation of both onion thrips and WFT, it’s difficult to determine the efficacy of Ference against either species alone. Our sampling on the second date was likely biased towards onion thrips, as we were focusing on varieties with the most damage. As many chrysanthemum growers in Ontario face a mix of both thrips species anyways, the distinction may be a moot point.

However, it should be noted that this was likely a RESIDENT population of thrips that had been building up within this greenhouse — meaning they may have been more susceptible to chemicals.  Thrips populations as a results of weekly importation of cuttings may not see the same effect due to potential resistance. Careful monitoring of thrips numbers and species will be needed when Ference is used to determine it’s efficacy on individual farms.

Ference for Whitefly:

With poinsettia season just around the corner, some of you may recall the chart below from this post regarding effective chemicals for Bemisia whitefly in poinsettia. This data was provided courtesy of researchers in the United States (you can see their full methods and results here).  According to their results, Ference stacks up extremely well against other chemical options for Bemisia B-species.

At the time of that posting in Fall 2019, Ference wasn’t yet registered for ornamentals in Canada.  As of March of this year, it can now be used in Canada to control whitefly species on indoor and outdoor ornamentals (including cut flowers).

Pesticides Tested

IRAC

Bemisia Control Using Chemicals ONLY

U.S. Trade Name (A.I.) Canadian Name (Status in GH Ornamentals) Nymphs Adults
Aria (flonicamid) Beleaf (registered) 9C GOOD GOOD
Altus (flupyradifuron) Altus (registered 2018) 4D  POOR* FAIR
Endeavor (pymetrozine) Endeavor (registered) 9B POOR POOR
Kontos (spirotetremat) Kontos (registered) 23 GOOD GOOD
Mainspring (Cynatraniliprole) FERENCE (now registered!) 28 EXCELLENT EXCELLENT
Safari (dinotefuran) (Not registered in CAN) 4A POOR POOR
Ventigra Ventigra (registered 2019) 9D GOOD to EXCELLENT FAIR TO EXCELLENT

*At high curative rates.  When lower rates were applied preventively, there was very little suppression compared to the control treatment (water).

hand lens vs leaf

Delphastus (the small black beetle in both pictures) is predator of whitefly eggs, and is especially useful for control of Bemisia whitefly in poinsettia crops. However, this biocontrol agent is VERY sensitive to chemicals, including Ferrence.

However, we all know control of Bemisia whitefly, especially in Poinsettia, doesn’t come without a few caveats. Recall these best management practices (which are true EVERY season) to avoid end-of-season whitefly explosions:

  • Remember that even “new” pesticide registrations may not work on Bemisia species that come in on cuttings. Due to the common practice of heavy pesticide use by poinsettia propagators, and earlier registration in other countries, resistance may already have developed in these populations.  If applied early in the season, you may see good knockdown of part of the population (the susceptible part…), but be prepared for follow-up applications to potentially fail.
  •  Because of this, it’s ALWAYS best to start your poinsettia season off with biological control, regardless of the chemical tools in our arsenal.  A period of pest management using only natural enemies allows the Bemisia B-species to become dominate over the Q-species (which is far more likely to develop resistance and cross-resistance to chemicals).  This means late-season applications of pesticides (if needed) have a better chance of working.
  • If you do need to turn to pesticides in late September or early October, always start with those “softest” on biological control agents.  Otherwise, you’ll have no where to go if chemical applications DON’T work as expected.  Unfortunately, according to the Koppert side effects database, Ference (cyantraniliprole) is extremely harmful to Delphastus, a key Bemisia egg predator and option for Bemisia “hot spots”, when applied as a spray.  So, this is likely a chemical you’ll want to save as a last resort.  No information is available yet on the compatibility of Ference with whitefly parasitoids such as Encaria and Eretmocerus, or it’s compatibility with biocontrol agents when applied as a drench (although this generally tends be a softer application method).

The Bottom Line:

To conclude this post, I want you to all hearken back to the days when Success (spinosad) and Intercept (imidacloprid) first came on the market for ornamental growers in Canada. What silver bullets they were going to be! Our pest problems will melt away! Huzzah!

Unfortunately, we know how those stories ended.  Resistance to Success developed in Western flower thrips populations in under 6 months… Intercept was only effective for Bemisia whitefly on Poinsettia for a few seasons.  And heavy use of both of these disrupted biocontrol programs.

Even IF Ference works on Bemisa this year, and continues to suppress thrips populations, resistance is a real threat with both of these pests. And, although compatible with mites, Ference may disrupt parasitoids or other biocontrol agents. Growers will have to be judicious in their use, and save this product for when pest suppression is a REAL necessity (i.e. sales are realistically threatened by damage or pest pressure).  Otherwise, we’ll be back to where we started – without any real chemical tools in our tool belts for two of our most serious pests.

Thank you to the growers and consultants who shared data to make this post possible, as well as to A. Summerfield (University of Guelph) for helping with sample collection and identifying all thrips species.

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