Rose rosette disease

Asked April 10, 2016, 3:11 PM EDT

Some of my roses are infested with this microscopic mite. Does anyone in the Portland area know this disease has now arrived from Southern states to the Northwest? Could there be some public emergency outreach before it decimates the Rose garden as well as privately owned landscapes?

Multnomah County Oregon

7 Responses

Thank you for your concern about a potentially serious problem for gardeners and their roses here in the northwest. Whenever rose rosette is suspected, we must be certain to rule out damage by herbicide, more specifically, glyphosate, the active ingredient in RoundUp, KleenUp, and other weed-killer products. It’s important to send me several images so that the identification of the problem can be verified.

So far, the facts of what are suspected to be a potential rose rosette infestation here in the northwest is this: Glyphosate was used during fall cleanup to get rid of weeds within, or near, a rose garden. The roses inadvertently received a non-lethal dose of the herbicide due to spray turbulence and/or a mild breeze which carried the chemical off target. The following spring, the new growth on the roses appeared as clusters of short, narrow shoots sometimes described as needle-like. Some plants outgrew the damage by the end of the season, others didn’t.

For images of glyphosate damage on roses:

- Diseases and Abiotic Disorders of Roses

- Roundup Damage on Roses

Please attach images of your rose when you reply to this email so that we can verify the source of the problem be that destructive mites or inadvertent weed-killer damage.

I am using a very prehistoric computer which does not recognize digital cameras. I can forward you an emailed photo of the roses in question, but I do not have a direct email address to do that. No Glyphosate was used in this garden or in any of the surrounding neighbor's gardens. The email I would like to send is from a client of mine - I am her gardener and two years ago she had to completely remove all plants and replace the soil in her front yard in order to eradicate this disease there. She has 52 roses in her yard and is justifiably concerned and very good at spotting abnormalities. We are both aware of what Glyphosate damage looks like. Thanks, Mary

When you respond to this email, you can attach an image(s) saved on your computer.

If that doesn't work for you, forward the images to with "Attn: Jean Natter - roses" in the subject line. I will there all day tomorrow, April 14, until 4 pm. (If the email is sent on a later date, respond to this email to say that it was sent.)

I was disappointed to learn that you were unable to send an image. I had hoped we might resolve the diagnosis but if we couldn't I had planned to suggest either a sample be submitted for testing (which you have decided to do) or that you contact the Invasive Species Hotline. If the diagnosis is verified as rose rosette, it's likely the lab will contact the Invasives people on your behalf.

If possible, please return to post the result of the tests, whatever the result.

I am going to send some pictures I took from my phone to your email. We will let you know results of lab tests. Mary

Thank you for emailing the images. I've attached 3 here, and will soon add another 2. (I'm omitting 2 images because they are essentially the same as the CAM00331.jpg.)

It's difficult to determine what is occurring with the roses. One thing for sure, we can rule out herbicide damage from glyphosate. But I'm uncertain we can call this rose rosette. The appearance as described by Clemson University (,s/plant_pests/flowers/hgic2109.html) is this:

  • Shoots and foliage have an abnormal red color
  • Stems appear thick and succulent
  • Rapidly elongating shoots
  • Shoots with shortened internodes
  • Stems with an overabundance of pliable thorns
  • New growth may have many branches that create a witch’s broom (similar to glyphosate injury)
  • Distorted or dwarfed leaves (similar to 2.4-D injury)
  • Deformed buds and flowers
  • Abnormal flower color
  • Lack of winter hardiness
  • Spiral cane growth
Too many of the above signs & symptoms are missing from the images you sent. The only image which displays any "excessive thorniness" is CAM00332.jpg and there's no way to determine, long-distance, if they are pliable as is typical with rose rosette.

The lab tests should resolve our questions.

If the tests are negative for the virus, I would investigate the cultural management. I suggest beginning with a soil test because some of the fertilizer "recipes" home gardeners use can cause soil imbalances of various fertilizer elements critical to a plant's well-being.