This is part two of my July 2014 article "Controlling Spider Mites and Thrips on Roses Without Insecticides-- Part One". In case you haven't seen it, here's that article:
http://theminnesotarosegardener.blogspot.com/2014/07/controlling-spider-mites-and-thrips-on.html
The underlying purpose of these two articles is to demonstrate that attracting, introducing and nurturing beneficial and predatory insects to control common pests like spider mites and thrips is both possible and desirable in a rose garden. I finally realized, after many years of spraying everything from organophosphates like Orthene, neonicotinoids like imidicloprid (Merit) and pyrethroids like Demand CS (which is what I thought I was supposed to do to control everything from aphids to Japanese beetles), that what I was really doing was wiping out naturally occurring beneficial and predator insects. For example, I suddenly realized that I no longer was seeing lady beetles and lacewings, which are natural predators for spider mites. It's no wonder because, instead of tediously picking Japanese beetles off my plants and drowning them in soapy water, I sprayed them with Demand CS, which works really well, but also wipes out all other beetles (like lady bugs) and just about every other predatory insect in the garden. As a result, I ended up with a massive infestation of aphids (something I hadn't seen in many years) because I had destroyed all their predators, in my efforts to deter Japanese beetles.
Then, early in 2014, my compatriot-rosarian Paul Zimmerman mentioned a new book by Jessica Walliser, "Attracting Beneficial Bugs to your Garden", which changed my way of thinking about controlling insect pests in my gardens. Here's a link to that book, which is available both new and used on Amazon:
http://www.amazon.com/Attracting-Beneficial-Bugs-Your-Garden/dp/1604693886/ref=sr_1_1?ie=UTF8&qid=1417916500&sr=8-1&keywords=attracting+beneficial+bugs+to+your+garden
Well, after reading Jessica's book multiple times, I decided I had to try what she advocates, and I learned a lot. First, the good news: I was very successful in controlling thrips without insecticides all last summer and, as a direct result, beneficial insects, including honey bees, bumble bees, mason bees, syrphid flies, lacewings and predatory wasps have flourished, on their own. Second, the relatively bad news: spider mites were harder to control than I thought, when I wrote my July article, above.
I washed my roses at least every other day and I just couldn't get rid of the spider mites altogether. Just when I thought I had the upper hand (as I did in July when I wrote the article) they would come back, not to the extent where I would see a lot of webbing, but just to where they would appear on new growth. If you were to look with a magnifying glass at the wilted leaf just under the bud in the picture below, you would find just a thread or two of mite webbing. So the wilted leaf is a tell-tale sign; something it has taken me a long time to understand. Those leaves die and become "crispy", as the mites multiply and move on to other new growth. I was able to control the mites by cutting off that leaf stem and washing the plant, but they continued to pop up elsewhere on other new growth, no matter how much I washed.
I really didn't want to use a miticide because I had imported large quantities of predatory mites (at least 100,000 cucumeris and fallacis mites) from California and I wanted them to do their job on both the mites and thrips, before applying a miticide, which would likely take down most of the mites, including predators. I made it until late August without using anything but water, but finally I had to do something because even my most resistant roses were succumbing to blackspot from the constant washing. In August, I made one application of Floramite and that took care of the spider mites. I won't know until spring if I killed all the predators (Fallacis mites are supposed to be hardy enough to overwinter in Minnesota) so we'll have to wait and see. I'm not giving up on this, however. Next spring I will start washing earlier and, if I can't control the mites with existing predators, such as lady beetles, which I didn't have in 2014, I will reintroduce more predatory mites. I still believe it will work if I get enough predators on the plants
Thrips (both singular and plural, i.e., one insect is called a thrips)
Given the persistence of spider mites, I was pleasantly surprised to find that I was able to control thrips with the beneficials I was able to introduce and/or attract to my garden this summer. Here's what a Carefree Beauty bud with thrips running around in it looked before my beneficials got to work. By the way, any bud that looks like this gets plucked and disposed of someplace where the thrips can't fly back into the garden. That's the first line of defense when you're not spraying insecticides.
As long as you don't spray things that kill them, natural thrips predators, such as minute pirate bugs and syrphid flies are fairly easy to attract to the garden with plantings, such as oregano, yarrow, alyssum and cosmos. And predatory mites can be imported from an insectary, such as Rincon-Vitova in California. In talking to Jan Dietrick, who runs Rincon-Vitova, I also learned that beneficial nematodes released in the soil of each rose bed will feast on the pupa of thrips, eliminating something like 80% of them before they become active on the plants. I ordered millions of the nematodes Jan recommended, as well as thousands of cucumeris predatory mites and 500 minute pirate bugs, in addition to 500 lady bugs for spider mite control. By the way, these beneficials aren't terribly expensive, compared with what I've been spending on insecticides. However, the required overnight shipping is quite expensive so it's advisable to combine as much as you can in one shipment. Here's Rincon-Vitova's website: http://www.rinconvitova.com/
I'm not sure exactly what did the trick on the thrips but, after they got off to a head start on me (see the picture above), I was able to control them from mid-summer onward. I'm pretty confident that the nematodes were effective and I could see the syrphid flies, which arrived in droves, probing around in the flowers, so I believe the combination of those two worked. The minute pirate bugs arrived too late to become well established, but I'm sure they will be around next summer, and I'm not sure about the predatory mites because they were too hard to see but I saw enough of them with my magnifying glass to know they were there.
Here's an interesting statement from an article on thrips by Applied Bio-Nomics, the producer of the predatory mites I purchased from Rincon-Vitova: "The first thing to know is that I do not believe that a single thrip has died from an insecticide registered against thrips for the past three
years .... I will bet you that they died from the soap effect of the spreaders and the stickers rather than the active ingredients. So,don’t even think about using chemicals against thrips.... Another even more important reason not to use chemicals is because there is now considerable research that shows that sub-lethal chemical attacks actually induce the thrips to lay more eggs. "
You can find this article and several other equally interesting articles on Applied Bio-Nomics' website: http://www.appliedbio-nomics.com/
So, according to this expert, a chemical like Conserve SC (spinosad), the insecticide of choice for thrips, doesn't kill thrips, it just kills the beneficials like syrphid flies and minute pirate bugs that attack thrips. This is completely opposite to what we have been taught to believe as gardeners.
Insectary Effects
Here's how a little insectary corner of one of my rose gardens looked last summer, with oregano, bachelor buttons, cosmos, dill, yarrow and a few other things to attract beneficials (Buck's Prairie Harvest is to the right). When I took this picture, this little garden was teeming with wasps, bees and other beneficial insects that were nowhere to be found in my garden last year. The idea of doing this, as well as directions on what to plant to attract various beneficials, came directly from Jessica Walliser's book, mentioned earlier. I plan to expand my insectary efforts next year, which will include removing several more roses to make room for more beneficial bug-attracting plants. In short, this really works!
Here's a picture of a bumble bee on one of my Earth Song plants last summer. I was really amazed at how many bees showed up in my gardens after I stopped spraying.
Here's another bumble bee on one of the many sunflowers I planted last summer to attract beneficials. I have no idea where all the varieties of bees (including many honey bees) came from but I did notice, with great interest, that the bumble bees were going in and out of a nest they had made alongside a drain pipe, just a few feet from where I had planted a stand of sunflowers to attract them. No coincidence there!
One of the most important things Jessica Walliser talks about early in "Attracting Beneficial Bugs to Your Garden" is the need to be patient. When there is a large infestation of insects like aphids or spider mites, it takes time to build up enough predator mites and insects to feed on them. I believe that's what my experience was with the spider mites this summer because I had killed off so many beneficial predators over the years, especially in my efforts to control an infestation of Japanese Beetles, which was especially bad in 2012. I have written several articles about that effort, but I now recognize that the use of the pyrethroid, Demand CS, which is very effective in deterring the beetles, comes at the price of eliminating many beneficial insects (about which a knowledgeable rosarian from the TCRC, Sue Youngdahl, gently reminded me at the time). I'm not going to use it again in my garden, as well as other insecticides, with the possible exception of an occasional miticide, as I did this summer but would really like to have done without. However, it is understandable that large public gardens and commercial growers do not have that luxury in their need to control Japanese beetles on a large scale, where picking them one at a time off the plants would be impossible (and those bugs are really awful and terribly destructive). For example, I noted that the University of Minnesota Arboretum was using a pyrethroid in their rose gardens last summer, which is completely understandable.
What I achieved in one growing season was remarkable and these results have made me want to try even harder next year. Nature is exceptionally responsive to our efforts to protect it, and my own most important lesson is that patience is everything, as we change our practices. The rewards are well worth the inconvenience and extra effort. I'll have more to say about this as we go along, so stay tuned and feel free to ask questions. We can learn together!
Jack
@mnrosegardener (Twitter)
December 2014
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