This disease problem was discussed in issue no. 7 of this newsletter. Some follow-up questions and responses concerning rose rosette follow.
Is there a test that can determine the presence of rose rosette disease? The exact cause of rose rosette disease has not yet been determined. A viruslike pathogen is suspected but has not yet been characterized. Once a pathogen is identified and characterized, tests can be developed to prove its presence. If a virus is found, an ELISA test could be developed based on the virus protein coat. If the pathogen is a viroid, it does not have protein, and a hybridization test with an RNA probe may be necessary to detect the pathogen. That test is more time-consuming and more costly. At this point, there is no laboratory test to confirm the rose rosette disease.
In addition to infected plants, should surrounding soil be removed/replaced? The soil itself is not infected, but roots and stems in the soil could be infected. The infected plants should be burned or bagged and removed from the site. This includes roots that might host the rose rosette pathogen. It should not be necessary to remove the soil.
Are any specific rose cultivars more resistant to rose rosette disease? As far as we know, there are no rose hybrids with rose rosette resistance. It would be best to assume that all are susceptible until information on resistance is available.
This disease is spread by grafting or by eriophyid mites. The question that followed is: Are there any beneficial insects or insecticides/miticides that target the eriophyid mites? It is known that not all miticides are effective against eriophyid mites. I spoke with University of Illinois entomologist Raymond Cloyd about this question. He said that there are no beneficials that would be sufficiently effective against the eriophyid mites. In terms of miticides, there are two that are available and might control this pest. One possibility is Thiodan (endosulfan), which Dr. Cloyd has seen work on a similar eriophyid mite and may still be available for purchase. The other possibility is Avid (abamectin).
Are there any environmental conditions that eriophyid mites seem to favor? Again, I defer to Dr. Cloyd. He said this depends on the species, and he is not familiar with specific preferences by this eriophyid mite. The mite is deep down in the meristem of the plant, so it is likely that environment has minimal impact. Always use the miticides only in conjunction with cultural suggestions provided.
We will keep you posted as more information about rose rosette disease is available.