Chilli Thrips (Scirtothrips dorsalis) defeated by oils and soaps

greentiger87August 17, 2013

I'm happy to report that I've been able to suspend the use of strong insecticides to combat chilli thrips, in favor of horticultural oils and insecticidal soap.

When chilli thrips initially infested my roses and other plants, it felt like an impossible problem. But I've found that consistent (weekly) use of either insecticidal soap or insecticidal oil that works through a physical mechanism (vegetable oils or horticultural mineral oils) is more than sufficient to eliminate the threat if started early in the season, and aggressively at the first sign of problems. Only the new growth and the base of the plant need to be sprayed, greatly reducing the workload and volume of spray needed. The undersides of leaves must be contacted by the spray, but this is relatively easy with the small leaves of new growth. Maintenance can drop the frequency to once every two weeks.

I spray either at night after the leaves have cooled or early in the morning. The base of the plant is sprayed to kill overwintering or otherwise maturing pupae - this is not strictly necessary.

Though multiple other low risk insecticides have proven extremely effective (spinosad and ivermectin), chili thrips are analogous to mites in their ability to quickly develop resistance to insecticides. Imidacloprid and neonicotinoids have well publicized issues, and are simply non-starters for me if there's any alternative. I think we should encourage even the use of low-risk insecticides only as a last resort. Obviously the practicality of using oils and soaps varies according to each person's situation, and this is not meant to be a moral judgement - just empowering information.

This post was edited by greentiger87 on Sat, Aug 17, 13 at 10:41

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michaelg(7a NC Mts)

Thanks, that is important good news. Are you in Florida?

    Bookmark   August 17, 2013 at 10:57AM
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greentiger87

I'm in Houston, TX. Chilli thrips were first positively identified here in 2007, but spread quickly. The population exploded during the extended drought of the past couple of years.

    Bookmark   August 17, 2013 at 11:10AM
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Brittie - La Porte, TX 9a

Thanks for the tip! I've heard of using oils and such before, but I was always afraid of burning the foliage to a crisp since the heat is way up. I'm interested in trying this out though. What did you use?

    Bookmark   August 17, 2013 at 1:20PM
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bart_2010(8/9 Italy)

Way to go,greentiger!!! Could someone post a picture of a thrip-eaten plant? Are Chili thrips different from regular thrips? I suspect I may have some kind of thrip, but it just eats the flowers of the roses, not the leaves...bart

    Bookmark   August 18, 2013 at 4:59AM
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michaelg(7a NC Mts)

Bart, everybody has flower thrips, which are very different from chilli thrips. Chilli thrips so far are mostly limited to Florida and the Gulf Coast, zone 9-10.

    Bookmark   August 18, 2013 at 10:59AM
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eahamel(9a)

The Houston Rose Society has a page on chili thrips. At the end, after discussing chemicals, they say that the gardener at the Houston Garden Center in Hermann Park, says he sprays every two weeks with insecticidal soap and there are no chili thrips on the hundreds of plants. This article was written several years ago, but last time I was there I didn't see any evidence of thrip damage on any of the plants I looked at.

May the Garden Center rest in peace, it's being torn down and rebuilt, rose garden torn out, too, and will be replaced with a new building and garden next year sometime.

    Bookmark   August 18, 2013 at 9:40PM
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lola-lemon(5b East WA)

I know I only have regular thrips (frankinwhatever) but I had them BAAAAD and maybe some of you will find this worth a try.
I tried spraying with something nasty once 4 years ago- (it worked, temporarily) but decided quickly it wasn't worth the health of myself and the planet to spray my garden routinely for thrips and so last year I switched to organic soaps only and added nematodes to the soil. It helped to a degree.
But I started this year with a pretty bad infestation (leaves more yellow from stippling, than green- all flowers scarred or just unable to open) and after watching my purchased lady bugs fly off, again, I decided I needed to quit killing aphids with the soap so the ladybugs would stay and lay some eggs, so then the lady bug nymps (alligators! who can't fly!) would be there eventually and eat the thrips.
... and doing nothing worked great.
I also had a bunch of minute pirate bugs and lacewings adopt my garden (yay! first time ever) and the thrips now have predators to eat them and seem to be gone. No more nose full of bugs when I sniff. I look to make sure there isn't pirate in there ready to bite me now tho! But No more ruined blooms.

I did a google search on "aphids and thrips" and found that some people agree- you need aphids to get rid of thrips. The aphids do so little damage, and they've been eaten up anyway now too.

So- I know I didn't have chili thrips, but I found that even the soap left me worse off than before for the regular thrips since it was removing all predators of thrips.
I don't have any other problem bugs in the garden I can't squish (no JB, no sawflies etc.) so I understand my solution isn't for everyone- just tossing this out for those who may only have a severe flower thrip problem.

    Bookmark   August 18, 2013 at 11:09PM
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JoshTx(8a)

I hate to be a debbie downer, but as I understand it (and living in Dallas) thrip activity dies down significantly during the summer. Even my roses beds (untreated) are thrip free for the time being.

It may be too early to tell that the oils and soaps were the determining factor.

Josh

    Bookmark   August 19, 2013 at 3:49AM
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amberroses(10a)

Josh, that's odd because in Florida the chilli thrip activity goes way up in the summer. In the cooler season, the thrips go away. Maybe you are thinking about regular flower thrips?

    Bookmark   August 19, 2013 at 8:04AM
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Brittie - La Porte, TX 9a

Yeah, I've actually been looking forward to September being here because it's one step closer to cool weather. I'm going to try the insecticidal soap next year. When you see the damage, you're really willing to try anything!

    Bookmark   August 19, 2013 at 8:42AM
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michaelg(7a NC Mts)

Josh, in Dallas you have flower thrips but probably not chili thrips. In my garden, flower thrips peak toward the end of the first flush of bloom.

    Bookmark   August 19, 2013 at 10:59AM
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saldut

I have chili-thrips again this year, bad.... I read an interesting art. in the Rose Soc. bulletin by geof. Coolidge, from Cool Roses in W. Palm ,, he says early in the spring work some systemic thrip-poison into the ground around the roses so they absorb it before the thrips wake up, I think he said Ortho , read the label instructions.. I searched HD also Lowes but neither store had any in stock... has anyone tried this? he also says to just dead-head during the summer, don't cut back as this encourages new growth, and the chili thrips love new growth and buds, and don't bother old growth..... I hope I recalled the gist of this art. correctly, I thought it made a lot of sense...and I'm going to try and stock up on the systemic before next spring and see if it's effective in my garden.... LOL, sally

    Bookmark   August 19, 2013 at 7:56PM
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bart_2010(8/9 Italy)

I, too, have heard that aphids get rid of thrips. My sad tale is that I used to have tons of aphids,but no thrips; I started spraying (my main hope was to get rid of beetles). It did nothing to the beetles, got rid of aphids , and now I'm pretty sure I have thrips (regular kind),since some "invisible bug" chews up the blooms so badly! So my new thing is : do NOT spray against insects! and hopefully Nature will balance things out again,and the aphids will come back...a sadder but wiser bart

    Bookmark   August 20, 2013 at 7:18AM
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greentiger87

Some thrips have a problem with high summer temps. Chilli thrips do not. I know they're still active because they're heavily damaging knockout roses that are used in the landscape around my neighborhood and town, and occasionally attacking other plants that I'm not spraying (papaya, hawthorne, hardy hibiscus, jasmine).

As for the actual products I'm using, I've used many - and haven't seen a huge variation in performance. The ultrarefined mineral oils (summer horticultural oil) are by far the least phytotoxic. In any case, I use them at night *after* the leaves have had a chance to cool down. As long as the leaf surface temperature is cool to the touch, and won't rise significantly in the next couple of hours, I don't see leaf damage. I've also used "Organocide". Finally, I've mixed plant oils directly with a surfactant (either soap or a non-ionic surfactant, sold as spreader-sticker). I've used canola, sesame, neem, karanja, mustard, as well as these oils infused with insecticidal spices/herbs. If there was any difference, I didn't see it. When used at less than ideal conditions, I did see light phytotoxicity when using plant oils.

I've used both Safer Insecticidal Soap (potassium salts of fatty acids) and Murphy Oil Soap (potassium salts of fatty acids, plus an amine oxide surfactant). Both work. Safer is slightly more expensive and easier on plants. When used in optimal conditions (low leaf surface temperature), I haven't seen any phytotoxicity from either product on roses. I have not tried using dish soap.

    Bookmark   August 29, 2013 at 11:03AM
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