Rose Rosette Disease

Rose Rosette Disease (Image 1) is a disease of wild roses that has now invaded home rose gardens. Not all roses get it, but they all can be susceptible. A few years ago it began to infect the very popular Knock-Out Rose. Until now, Knock-Out Rose was a very low maintenance plant but this disease has changed that. Distribution of Rose Rosette Disease is indicated in the map on (Image 5). Unfortunately when a rose gets Rose Rosette Disease, the only thing that can be done is to dig the plant up, roots and all, and immediately put it in a bag or burn it.

 Infection is believed to start with rapid growth of a new shoot, with clusters of small branches and leaves forming and remaining reddish in color. These are called a “Witches Broom” (Image 2). The stems that develop are thick and have a proliferation of thorns (Image 1,3). In (Image 3) the stem on the left is a non-infected stem with an infected stem on the right. Infection may be first indicated by reddish colored leaves that never turn green. Roses get this disease– which is a virus– by transmission from an eriophyid mite (Image 4). These mites are very small and can only crawl or be spread by the wind (they can not fly). Infection can also be spread with pruning shears. When pruning, disinfect the sheers when moving from one plant to another.

Control

There is no cure for the virus.  Once infected, removing and destroying the plant as quickly as possible is recommended.
Some research has suggested that prevention may be possible by controlling the mites before infection. In a two year study, two products have shown effectiveness; it involves alternating application of these products every two weeks throughout the growing season.
First apply ferti•lome® “Green” Label Horticultural Oil. Always spray on well hydrated plants in the very early morning. Thorough coverage with this oil is required, so cover every part of the plant.
Two weeks later, apply Hi-Yield® Bug Blaster II with Bifenthrin.  Thorough coverage is recommended but not quite as critical with this product. This recommendation is preliminary but it is the best option as of right now.