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Rose Rosette Virus Identification and Control

 

What is Rose Rosette Virus?

One of our beloved landscape plants, the rose, has been increasingly affected by this virus, which is spread by tiny wind transferred mites.  Symptoms include thickened stem growth, excessive thorns, witches’ broom growth at end of stems, branch die-back, discolored and distorted leaves.

The above image shows the excessive thorn development on an affected rose. The symptoms of the virus can be fairly easily seen year round; this picture was taken in January of 2020.  This particular rose showed no symptoms all spring, summer and even fall.  After a late fall warm spell, the rose sprouted symptomatic new growth.

Prevention of Rose Rosette Virus

  1. Prune around Valentine’s Day each year.  This will remove mites that might be overwintering in flower buds or seed heads. Dispose of pruned material; avoid composting in case mites or the virus is present. Tips on how to properly prune roses can be be found in this video.
  2. When doing yard clean-up, avoid using blowers.  As we mentioned above, mites are often wind transferred and gusts of air can spread them through the landscape.
  3. Space roses well. Plant so that at mature size, leaves from one plant won’t touch another.  This could reduce the occurrence of mites walking from one plant to another.  Proper spacing also increases air flow which will help reduce the occurrence of other disease issues such as black spot.
  4. If you have been around infected roses, wash your hands, gloves, and clothes before working in the garden. All could have picked up mites. While the virus that causes rose rosette isn’t able to survive long outside of the plant, virus spreading mites may be present on your shovel or pruners.  Clean tools with household disinfectant or a bleach solution before using them in the garden again. Overkill? Maybe, but mites are so tiny (1/200th of an inch) that they can easily hitch a ride on you or your tools.
  5. When designing your landscape, consider using alternative plants (see list below).  There aren’t any other plants that offer the exact same features as a KnockOut or Drift rose but there are some wonderful re-blooming shrubs and others with outstanding foliage color.

The above image shows witches broom growth, which is the tight cluster of stems, leaves, buds and even flowers near the end of branches. This odd growth pattern is obvious even in winter months. If you think your plant may have rose rosette, take pictures and email them to us or bring a sample for identification (keep sample contained in plastic bag to help prevent spread).

Control

Unfortunately, there is no cure for this virus and affected plants will need to be removed and put in the garbage. Do not compost or burn the affected materials.  For existing, unaffected roses, treat with dormant oil after cutting back in February, which could help control overwintering mites. Remove any fallen leaves or debris. Spraying with harsher chemicals could reduce the beneficial insects that feed on the mites.

If you have just one plant showing symptoms, remove that plant only and follow the prevention tips above to help control the spread. Although this disease can take years to kill a plant, during this long decline, many other roses may be infected by it (mites being wind transferred to unaffected roses). We recommend removing symptomatic plants as soon as they are identified as such.

At this time (January 2020), Top Gun rose is the only resistant variety (and no variety has been proved 100% resistant) but research is ongoing.  It would be best to avoid replanting with roses for at least one year if your landscape has been overcome with this virus.  This is due to the fact that the virus may still be in remaining roots left in the ground after removal.  Mites may have also already infected nearby roses, meaning that the virus could continue to spread onto newly planted roses.

Alternative Plants

While no plant can completely replace the April to November blooming period of KnockOut and Drift roses, here are several wonderful, hardy plants that offer either bright, long season blooms or colorful foliage all season long.

Sonic Bloom weigela

Encore azaleas

Dwarf or semi-dwarf butterfly bush

Crimson Fire loropetalum

Dwarf crepe myrtles

Kaleidoscope abelia (and other dwarf varieties with foliage color)

Compact nandinas

Recovering from a substantial rose loss?  We understand that it can take time to move past it; our team will be here to offer suggestions when you are ready to replant.