Wednesday, July 23, 2014

Controlling Spider Mites and Thrips on Roses Without Insecticides-- Part One

Author's Note: I started writing this blog in early June, when I decided that I was going to try and get through this growing season without insecticides, in order to attract and keep a population of beneficial insects in my gardens, which would attack the undesirables,i.e. two-spotted spider mites and thrips.  Frankly, I didn't want to publish this and then find that my methods weren't working. Well, here we are more than a month later and I'm very pleased to report that the only thing I've sprayed this summer is lots of water for the spider mites; plus I've imported from California large quantities of predatory mites (at least 100,000), nematodes (millions and millions), lady bugs (500) and minute pirate bugs (500) to attack both spider mites and thrips.  Bottom line: It's working!  In part one, I'll deal with spider mites, which are fairly simple to control with water and predatory mites, and then, in part two, thrips, which present a more complicated challenge.

Two-Spotted Spider Mites 

I've always had problems with spider mites. I've tried just about everything to get rid of them, but they just keep coming back.  I've spent a lot of money spraying miticides/ovicides, only to find that the mites are either not completely taken down, or there are still enough eggs hiding in and around the plants to start up new generations.  I have also known for years that water, sprayed in a sharp stream on the underside of plant leaves, is very effective in removing mites.  Once you knock the mites off the plants, they can't get back on and they die, so what's left on the plants are the eggs for the next generation.  I've been reluctant to do this, however, because water-washing 100-plus roses every three or four days (to hold down new generations of mites) has always seemed like a lot of work, plus it flies in the face of the conventional wisdom of not top watering roses.  Well, experience has taught me otherwise, and here's why.

I do a lot of propagation work, both with stem cuttings and air layering, and consequently I always have several plants under lights during the winter.  These plants always develop spider mites, which means I'm bringing mite eggs into the house on these cuttings/air layers.  And that proves that the miticides/ovicides I've been using aren't working.  I always wash these indoor plants with sharp streams of water in our laundry sink (which is messy when the plants start getting big) but, as long as I'm diligent about washing every three or four days, the mites go away.  So, I know washing works and I asked myself why I didn't just do that outside?

Miticides are expensive, especially those that contain ovicides to try and kill the eggs.  For example, an 8 ounce bottle of Forbid, a miticide/ovicide, which is the best product I've used because it's translaminar, meaning that it penetrates to the bottom of leaves to kill both the insect and its eggs, sells for $245, on sale from $289 at Rosemania.  That's more than $30 an ounce!  It works for a while, after a couple of applications (which it ought to at that price), but, as mentioned above, I've proven that the eggs are still there. I've also used Floramite, which has an ovicide in it but is not translaminar, and it really doesn't compare with Forbid in effectiveness, so it really has been unsatisfactory for me.  It's not cheap either, on sale at $119 for 8 ounces, down from $125, at Rosemania. Avid, which I used for many years, is just a miticide, with no control for the eggs.  This one needs to be sprayed every three or four days to kill successive generations of mites, and it works, if you are diligent, but really it does essentially the same thing as water, sprayed in the same regimen.  Avid isn't cheap, either, at $100 for 8 ounces.

The over-riding downside of these products is that they are relatively dangerous. You must wear protective clothing and you must wear a mask so you do not inhale them.  This is no joke. I had a bad experience, which caused lung problems for years.  Thankfully, it has gone away, but now I won't spray anything (except water) without a full-face 3M respirator and a Tyvek suit.  See my post on protecting yourself:

So, I asked myself this spring, after successfully controlling mites indoors with water all winter: Why don't I substitute a little sweat equity for all those expensive and dangerous chemicals on my shelf and just diligently wash the spider mites off my roses every couple of days this summer?  So that's what I've been doing for the last couple of months and I've been quite successful, although I'm still finding pockets of mites, as evidenced by a bud bending over here and there, which is a sure sign something is attacking the plant (see picture below).  On inspection with my magnifying glass, I invariably find webs and, after plucking that bud, I give the plant a special washing, paying special attention to all the buds and new growth on the plant.  This one, for example, had just a few webs on it but the damage had already been done.  This is also also a symptom of thrips or rose midge.

In the July-August 2014 issue of "American Rose", Rich Baer refers to this problem as "Funny Bud" and his "nonscientific conclusion" is that: "Funny Bud occurs when the normal development of the petiole is altered and the cells that are dividing to produce the petiole go astray and produce a leaf."   I think Rich is a great photographer but I beg to differ with his "nonscientific conclusion" here.  My experience is that funny bud is always an indication that the rose is under attack by insects (which, of course, could be what's making the petiole go astray).

Bottom line: Never leave a bud like this on the plant; get rid of it in a way that the insects can't spread. That's especially true of thrips and midge which have wings and will find their way to another plant.  Funny buds never produce good flowers and they need to go.

How to do it

The other day, I asked my good friend Susan Fox, rosarian par excellence in southern Illinois, what she does for spider mites.  After kind of growling into her cell phone, she said:  "I just spray them with a sharp stream of water; that's the only thing that really works.  None of the expensive miticides do the job as well as water".  I couldn't have said it better; so we're on the same page!

There's no secret about this either.  There are three or four mentions of this method in the July-August "American Rose" alone, including a quote from me in Susan's article: "Some Like it Hot".

I use several water spraying methods.  I have a great water wand that was advertised in the "American Rose" for many years by Walter Vinton in Springfield, MO.  It sprays a high-pressure fan of water directly upward, which allows me to get under each plant and work upward to the buds.  Unfortunately, Walter passed away and the product is no longer available. Here's how it looks:

I also use an old fashioned brass twist nozzle that is available in most hardware stores (as opposed to the big box stores, which seem to have lost track of such things).  Usually the sprayer head on watering wands is removable and you can replace it with a standard brass nozzle like this:

For my readers in Minnesota and Wisconsin, I found this wand at Menard's in Minneapolis ($7.99) and it actually makes a pretty good mite blaster, with the hose nozzle attached.  It is particularly effective in spraying the tops of the roses, i.e. the buds and new growth, and you can do it from a distance, if you see some evidence of mite damage.  You can vary the intensity and, with the curved tubing, you can also direct a sharp stream from the bottom of the plants (see photo below):

Early in the season, when the mites first appear, it's important to wash your roses at least every couple of days, for a few weeks, until all signs disappear. You can then revert to every four days or so, while paying special attention to hot spots, where mites seem to be the hardest to control.  Theoretically, the mites regenerate every four days from the eggs left on the plants and in the soil.  Remember, however, that there are likely to be several generations of spider mites in your garden, so they could be regenerating every day for a while, until you get them under control.  If you keep washing repeatedly, you should be able to kill off all succeeding generations, such that fewer new eggs are being laid.

And remember, at the same time, you're also washing aphids off your plants.  That's a plus!

Make no mistake, it's a lot of work to wash 100+ roses every two days, but it does ease up after a while, as you start to get control of the majority of the roses.  Hot spots on certain plants will remain and those need to be tended to every day or two.  If you see wilted or "crispy" leaves on new growth, that's a sign that mites are present (see a hot spot plant below).

I aggressively wash these wilted leaves and then all the new growth around them.  Then I pluck those leaves and throw them away.  They will die and become dry or "crispy", so there's no point in leaving them on the plant.  They will definitely not recover.  Note that the leaves below show no signs of mite damage; they are just on the new growth, so that's where I concentrate my washing efforts. The folks at Rincon-Vitova Insectaries in Ventura, CA, where I acquired my predatory mites, say they work from the bottom of the plant upward, forcing new generations of spider mites upward onto new growth.  That seems to be exactly what I'm experiencing, as in the above photo.  So all of my washing is on the new growth at the moment because that's where the damage is continuing; plus I don't want to wash off the predatory mites at the bottom of the plants.  Unlike spider mites, however, they can climb back on the plants and get back to work!

The downside of washing roses that are susceptible to black spot is that the fungus spores will eventually find their way onto the leaves from all the splashing.  Even though most of my roses are disease-resistant (by design), I am beginning to see black spot, here and there, in the third week of July, after two months of washing.  So, I'm about to spray a first round of Mancozeb (Manzate), which is the only fungicide that actually kills the spores, as opposed to just "controlling" them.  This will be the first time I will don my Tyvek suit and full-face respirator this year, so I'm quite pleased with the results of my no-spray efforts thus far.

For more information on treating black spot please see my July 2012 blog "There's a Fungusamongus":  .

Finally, the upside of washing your roses on a hot summer day is that you get a little wet.  It always reminds me of running through the sprinkler when I was a kid; a very long time ago.  So it's fun work :)

Please feel free to ask questions about anything, either here on the blog page or directly by e-mail to: .

In part two of this article, I will talk about my experience controlling thrips with beneficial insects and nematodes this summer.  It's working!

Good washing... and stay tuned to the Minnesota Rose Gardener.



  1. Thanks for the excellent tips, Jack.

  2. It is possible to plant a trap crop to see if thrips are present. Asters, petunias, and fava beans are all crops that will show signs if thunder flies are present and if they are introducing any viruses. Leaf spots, oozing brown patches, dead leaves, and concentric rings of varying colors are all symptoms that will present themselves if thrips are existing in the area. Several thrips treatments can be applied to fix a problem.

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  4. I hate having to do this but it's getting out of hand. My loft is infested with spiders and now its spreading to the rest of the house. I would rather be able to manage their numbers than kill them if possible. Its the cobwebs everywhere that I find difficult to put up with. Any suggestions welcome.

    1. Spider mites on plants and spiders in your house are very different things. They are both insects of the arachnid family but not at all similar in how they are controlled. I know very little about controlling an infestation of spiders in a house but I would imagine some sort of insecticide spraying would be necessary. Do you live someplace where commercial insect exterminating services are available?