Mandevilla IPM Program Part 4: Putting Together a Cheaper Spray Program
This last post in this series summarizes the strategy behind the spray program for Thrips parvispinus control in mandevilla in Ontario.
After several years of refinement to bring down costs while maintaining efficacy, several growers have been using this program, or some version of it, for several years. This program focuses on critical “spray periods” versus weekly spraying, and takes advantage of spot sprays, focusing on sensitive varieties.
That we’ve found a successful and economical program in mandevilla is quite an achievement, given the lower number of pesticide available for this pest in Canada versus the U.S., and the long growth period of the crop (July – April).
Read on for how we’ve put this all together through trial and error, and for cost comparisons to more traditional spray programs.
Critical Spray Periods for Parvi in Mandevilla
When Parvi first came on the scene (Figures 2 and 3), many growers attempted weekly pesticide rotations. This made sense in terms of a) trying to avoid resistance by rotating modes of action (MOAs), and b) staying on top of a pest that reproduces quickly at high temperatures.
While this DOES work, it also means suiting up each week, and can add up in terms of pesticide and labour costs. A greenhouse I was working with wondered if there was a better way. Could we find a few points in time where sprays were most effective without risking damage that would delay the crop? After several years of weekly scouting at a commercial operation, we found that there are 4 critical periods for Parvi control in a typical mandevilla program (see Figure 4 for approximate pictures of these crop stages):
- 1st: the end of propagation, which we discussed in the last post. Larvae are the most common life stage here, so products that act on larval stages (“larvicides”) should be used.
- 2nd: Mid Fall (e.g. late Oct or early Nov), before the crop goes into lower growing temperatures (15-18C). This is the most critical of all the spray periods. Products with both adulticide and larvicide properties should be used to knock back the entire population. If a noticeable amount of Parvi is still present at this time, the crop won’t put on any new growth under cool growing temps. We’ve learned the hard way that Parvi will keep slowly trucking along at these temperatures, and even 1 or 2 larvae attacking growing tips prevents proper growth. The good news is that here, optimal spray coverage can be achieved, as the plants have been cut back and/or the trellis isn’t in the way yet.
- 3rd: Late Winter, when temperatures start to rise. Low numbers of Parvi can quickly get out of control when there are 2 or 3 sunny days in late February. The crop may be trellised, but usually the canopy isn’t dense enough yet to prevent good spray coverage. Here, preventative applications of larvicides should be used, as well as M52 for adult suppression.
- 4th: Clean up right before sale. In a perfect world, we wouldn’t need this 4th spray period, if we get on top of Parvi in the previous 3 time points. Complete clean up is difficult at this time, due to the presence of adults in trumpet flowers and a dense crop canopy. However, spraying plants before they go over the border is important to avoid having shipments rejected.
Note that these critical periods are only relevant IF your main source of Parvi infestation is the mandevilla cuttings themselves. If you are in the Southern U.S., where Parvi pressure can come from outside, this won’t apply.
Additionally, if you are in a Northern greenhouse growing lots of tropical crops, and if there’s Parvi pressure in the same or nearby compartment as your mandevilla, this probably also won’t work. I’ve worked with a grower in this situation, and although we were mostly able to stick to the program, we needed a lot more spot sprays along the leading edge of the infestation point. If you do grow multiple tropical plants that are hosts for Parvi, consider isolating your mandevilla in a smaller compartment away from other sources of the pest to reduce program costs.
Putting Knowledge into (Spray) Action
Delayed Applications – Why it Works
Now that we know the critical periods for chemical applications for Parvi in mandevilla, how do we use this information to lower program costs?
By treating at the first time point (plugs right out of propagation) and lowering Parvi levels at the beginning of production, you can delay the need for additional whole-compartment sprays from August until late October. Or potentially even into December.
Delayed sprays work simply because we have several chemicals that can reliably knock Parvispinus outbreaks back in mandevilla, even if numbers are fairly high in October/November. Figure 5 shows an on-farm trial we did in 2022/2023, the second year after Parvi was found in mandevilla crops in Ontario.
Despite starting with an average of 20-35 THRIPS PER 9-INCH POT, we were able to knock the Parvi back to undetectable levels for almost 16 weeks! This was done using a “sprench” of Success and Beleaf (not something I would do now, due to costs and rate concerns, but it worked).
Prior to this, only predatory mites and mass trapping had been used to (unsuccessfully) manage Parvi. We used a rotation program going forward, and saved Pylon for Spring clean up in April. Despite the inauspicious start, 100% of the plants were sold by May, despite high Parvi levels in the Fall.
The other reason delayed sprays work is because Mandevilla has an AMAZING capacity to grow out of damage and still stay on track (see Fig. 6, below).
Figure 6. Left: A variety of mandevilla showing significant T. parvispinus damage in late February. As these plants were probably garbage, we used them for phytotoxicity testing of Kontos and Pylon. Right: the same plants cleaned up by the test pesticides in time for sale. All plants grew out of the damage and flowered in time for sale (April). Photos by OMAFRA.
Delayed Sprays – When to Commit?
So, instead of chasing every single Parvi adult or larvae you see with weekly sprays, ask yourself a few questions BEFORE you commit to spraying the whole compartment:
- Am I seeing Parvi in every variety? Or just a few Parvi here and there or in hot spots?
- Am I seeing both adults and larvae? Or mainly larvae?
- Am I seeing widespread damage? Or is it just in a few sensitive varieties?
- Are the plants not putting on new growth (leaders) as expected?
- Are the Parvi noticeable on leaves and growing tips, not just the open flowers?
- Is the average number of Parvi above 5 thrips /plant? For most varieties? (You can sample just flowers, or inspect 5 plants per variety).
Unless the answers to the majority of these questions are “Yes”, you can hold off spraying for a week or two, as long as you do diligent weekly scouting to keep an eye on the problem. Delaying sprays by a few weeks can get you closer to ONLY having to do the critical Fall cleanup step (even if you have to do it a bit early), saving you money.
Some of this requires growers and owners being able to tolerate some level of Parvi in the crop, knowing you can clean it up later. It also requires regular scouting, to objectively monitor your Parvi levels. Look for both presence of adults and larvae on flowers/leaves, as well as tell tale signs of Thrips parvispinus damage.
Delaying widespread sprays until Fall Cleanup doesn’t mean NO sprays. Generally, after potting, many growers do need to manage pop-ups of Parvi in susceptible varieties or sizes with a few spot sprays. You can choose a product like Rimon (novaluron) or Kontos (spirotetremat) if you see more larvae than adults, and Lalguard M52 if adults are also present. Spots sprays really work for this pest because it is SO variety specific, which we’ve talked about in other posts.
Optimal Spraying for Parvispinus
If you are going to delay sprays, then the other necessary component of this strategy is good coverage when you DO spray. One effective technique we’ve found for thrips specifically is to do 2 applications of a product 5-7 days apart. This is especially important in the Fall Cleanup stage.
Why two applications, you ask? Well, it has to do with the unique life cycle of thrips compared to other pests in the greenhouse. See Figures 7 and 8, below:
The benefits of doing 2 applications can also just be mechanical – you’re more likely to hit leaf areas you may have missed the first time with a 2nd application. Make sure to always follow spray intervals listed on the legal label, which you can find on Ontario’s Crop Protection Hub. (E.g. for Pylon, this is a min. interval of 5 days).
Case study: Program Comparisons at a Commercial Operation
A commercial mandevilla grower I worked with had 3 separate growing compartments. So in 2022, we decided to take advantage of this and test competing programs, looking at their efficacy AND costs. Recall this was fairly early after Parvi was first found in Ontario in 2020, so some of the products tested were just guess work.
The Programs
We tested out 3 programs, which included:
- A. Traditional chemical pesticides started early in the crop; the whole crop was sprayed each time. Applications were made weekly at the beginning of the crop, then based on scouting after fall clean up.
- B. Starting with soft (microbial) pesticides and then shifting to harder chemicals for clean up. The whole crop was sprayed each time. This program was designed like an IPM program for Bemisia whitefly in Poinsettia, before we knew how likely Parvi was (or wasn’t) to develop chemical resistance.
- C. Focusing on spots sprays in varieties and sizes that needed it. The entire compartment was only sprayed 2 times – during “fall clean-up” and “spring clean up”
Table 1. Comparing different experimental pesticide programs for Thrips parvispinus in mandevilla. Trials were done at a commercial mandevilla grower in 2022/2023. Note that DDVP has now been fully deregistered in Canada.
| Timing | Program A – Early Chemical Sprays | Program B – Microbials + Delayed Chemical Sprays | Program C – Strategic Spot Sprays of Pesticides |
| Aug-Oct | DDVP 6x – whole crop | Rotate M52 & Bioceres WP weekly (5x) – whole crop | Kontos, Rimon, Rycar, M52 on problem areas; Kontos drench on 12″ whites ONLY ; Success 3x, Avid 3X on white 14″ ONLY |
| Oct – Dec | Kontos, Rimon – whole crop | M52 2x, Bioceres WP, Rimon 2x, Spear T – whole crop | Pylon 2x – whole crop; remove flowers between 1st and 2nd sprays to improve efficacy |
| Dec -Feb | Pylon 2x – whole crop | Success 3x, Avid 3x, Pylon – whole crop | Success 3x, Avid 3X, Pylon 2X on problem sizes ONLY (2-3 houses in 1 zone) |
| Feb- Sale | Success 3x, Avid 3x – whole crop | Rimon 2x, M52; Avid 4x, Success 3x, Pylon 3x on whole crop | Pylon 2x – whole crop |
| COSTS | $830/10,000 sq ft Caveat – smaller zone, DDVP only suppressed Parvi. | $2000/10,000 sq ft Weekly microbials expensive; lack of efficacy with Success late in season, possibly due to resistance | $378/10,000 square feet Would be $2060/10,000 sq ft if sprayed the entire zone each time |
Outcomes and Cost Comparisons
With the exception of Program A, the choice of chemical (adulticide and/or larvicide) and when to spray were made based on weekly scouting observations, so scouting labour was similar between compartments. Our cost comparisons focused on the cost of the product, not of the labour involved with each spray. See Table 1 for the breakdown of the chemicals used and a cost comparison by square foot
MAIN FINDING: Spray programs were all the same in terms of efficacy. All plants were able to be sold at the end of the season with low damage. The biggest difference was cost. Focusing on spots sprays reduced costs from 54-81% compared to whole compartment sprays, regardless of whether conventional or microbial pesticides were used.
The cheapest program by far was Program C, where we focused on spot sprays of varieties and sizes that needed it. This included my arch nemesis – large sizes of Summerstar White – along with some 11 inch baskets that seemed to flare up (mixed colours). By focusing on spot sprays, we were able to use some of our most effective (but expensive) chemicals for Parvi, but in a smaller area, reducing costs.
A good example is a drench of Kontos on the 12-inch whites – this was definitely the single most expensive application across all 3 programs in cost/sq ft. But given the small area, and how Summerstar white, specifically, can build up large populations of Parvi that can spill over into other colours, it ended up being a good investment. Note that if we HAD done every application across the whole compartment each time in Program C, this would have instead been the MOST expensive program.
Note that spot sprays also have the added benefit of reducing the chances of pesticide resistance developing. Leaving some susceptible thrips in the rest of the greenhouse to mate with any resistant thrips often results in offspring that are susceptible or only partially resistant.
Unfortunately, the microbial program (B) was the most expensive, because we ended up having to use a lot of sprays to get suppression. We now know that wettable powder formulations generally don’t work that well for Parvi, (unless you are combining them with Suffoil X as a dip). Unfortunately, more than 3 applications in a row of an oil formulation can risk phytotoxicity. Microbials like M52 are better used in rotation with other softer chemicals, like Rimon and Rycar, or if you want to suppress Parvi while doing spider mite biocontrol.
What we changed in 2024 and Beyond
When we were initially playing around with these spray programs, we figured we would need BOTH Pylon and Success as our “big guns” for cleanup.
Unfortunately, testing of Success showed that higher-than-label rates were needed for the efficacy (up to 10x), increasing the cost of the program by QUITE a lot.
In the PDF of our final Mandevilla IPM program (below), you can see that we’ve eliminated Success for this reason, focusing on Pylon as our main clean-up chemical.
As long as you rotate with other chemicals (e.g. Kontos, Ference, Rimon, M52) if you need to spray the whole compartment, you shouldn’t run into any resistance issues relying on just Pylon for Fall/Spring clean up, and for spot spraying program crops.
Take Home Messages From Part 4
- Remember, this is just one plan I’ve come up with working with certain growers. Reps from other biocontrol / pesticide companies may have other effective plans as well. Feel free to take this scaffolding and adjust it to fit YOUR operation and your needs. Just make sure you are balancing costs with efficacy across all 3 major pests (Parvi, TSSM and Oleander aphid).
- Focusing on “critical spray periods” over weekly sprays only works if you’re willing to spray properly, meaning GOOD spray coverage (especially on sensitive varieties), and repeating sprays within a critical 7 day window.
- Don’t forget the mechanical controls (Figure 9). In our studies, removing the open flowers between the 1st and 2nd pesticide applications during Fall Cleanup was more effective than doing a 3rd pesticide application. I also think it helped our pesticides last longer – up to 16 weeks of control in some cases! Adding dark blue trap cards (Parvi prefer the shade of the Russell IPM cards) is also a no-brainer, as any adult removed from the population is one less to breed in your greenhouse.
- Spot sprays, while saving costs, can also help manage pesticide resistance, as you aren’t exposing your whole Parvispinus population to as many chemicals. Resistance has already been seen in some Ontario greenhouses to Ference (cyantraniliprole) and Success (spinosad).
Download the Current Mandevilla IPM Program
Acknowledgements
Phew! This feels like the end to a life chapter for me. This blog series and the related webinars have been the result of 6 long years of learning everything I could about Thrips parvispinus, and providing all of you with a brain dump.
I could NOT have done this without several amazing farms, their growers and IPM staff. I cannot thank the farms enough that let me in their doors, either weekly or just once or twice, to play with their Parvi. Your trust and willingness to experiment has meant SO much and helped the industry TREMENDOUSLY.
I also never want anyone to think that I’ve come up with all of this on my own. The years of experience of the growers and the dedication and observations from their IPM staff were critical. As were the many, many discussions, arguments and recommendations from various consultants and technical reps in the industry, including:
- Ronald Valentin, now at Mastronardi Produce
- Ashley Summerfield, Rose Buitenhuis and everyone at the Biological Crop Protection Lab at Vineland Research and Innovation Centre
- Judy Colley, Veronica Cervantes and Beth Bylsma at Plant Products (part of Biobest Group)
- Mike Short, Eco Habitat Agri Services
- Kelly Smith Consulting and Strategy, formerly of Biobee and Scoutek
- Sarah Stuive and Jenna Straughan at Global Horticultural
- The amazing research coming out of the Revynthi lab at the University of Florida, along with Lance Osborne at UofF.
- Suzanne “The Bug Lady” Wainwright Evans
- And probably many others I’m missing!
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