Are there false alarms?

Yes. Spray damage, herbicide drift, discolored canes, blind shoots, some rootstock suckers and freeze damage- all can be mistaken for RRD. Even normal growth for an inexperienced rose grower, can be a false alarm. If in doubt, you can spray the area to prevent spread of infected mites and watch to see if the rose grows out of it. An RRD infected rose won't get better. See Chapter 12 "Avoidence of Rose Rosette in a Garden" - Part 4 - Chemical Control of RRD for more information on miticides. We use Cygon 2E.

HERBICIDE DRIFT OR RRD? A recurring question is, "Are these symptoms of rose rosette disease or are they symptoms of herbicide drift?" There is a very basic, but commonly overlooked difference between the two maladies. Herbicide Drift affects herbaceous material that has already formed. Roundup, for example, affects leaves that are there when the herbicide is applied. (There is some argument as to whether or not Roundup routinely affects woody material, apparently it can in some cases penetrate the wood to the cambium). Nonetheless, the distortion that results will be of the leaves that are already present.

Herbicide drift will not affect an inner cane on a large rose without some effect on the surrounding canes.

It should be noted that RRD symptoms occur on new growth only, where as herbicide drift would harm both new and old growth. This is a big difference. If a leaf is there when the infection carrying mite lands, that leaf will continue to have its form, unaltered. But if the base of that leaf is the locus of first infection, the axiliary buds at that base of that leaf will grow and grow outrageously, quickly overshadowing the growth of the first leaf. Where the first leaf is just a leaf, the axilary buds may and probably will become full grown stems with contorted leaves spaced with short internodal distances, forming a rosette of leaves of varying degrees of distortion. I have heard so many times, "but what if it's herbicide dammage?" Seldom do they follow up with the logical response, "but what if it's not?"

One other difference which may not help in making a timely judgment is that RRD is graft transmissible and herbicide damage is not.

FREEZE DAMAGE OR RRD? Be mindful of recent weather. Was there a freeze? Especially a late Spring time freeze? If in doubt, compare damaged canes and foliage to other bushes equally exposed. If you are still not certain, spray the suspect bush and surrounding area and watch the bush. Remove the damage and see if it grows out normally. An RRD infected bush won't!

ZINC DEFICENCY OR RRD? A person who is knowledgable about roses to the extent that he has books such as 'Horst's Compendium of Rose Diseases' in his library, might recognize one of the Spring RRD symptoms as a zinc deficency. A test to see if it is actually a zinc deficency or rose rosette disease is quite simple. A zinc deficency should affect the entire bush, the roots would not take up zinc and send it differentially to some canes and not to others. RRD, being a disease of the canes at first, can affect the bush one cane at a time, so you can have perfectly normal canes from last year along with those showing symptoms.

NORMAL HEALTHY GROWTH: New growth on roses is often dark red, and then the color changes to normal green. This varies with cultivar and is normal. Other things such as bagworms, a bird nest or even a stray weed in a big rosebush can look like witches' broom from a distance. That's why you need to know the entire rose not just the blooms.