Rose Rosette Disease: Dallas Is the Epicenter

Rose Rosette Disease called RRD and Knockout Rose Disease manifests itself with elongated and bright red branching. Knock Out roses and Drift roses are especially susceptible. RRD began appearing in about 2009 in Dallas.

Knockout Rose Disease Elongated red branches contain microscopic mites

Elongated red branches known as “Witches Brooms” contain microscopic mites.

You will see the pointed, elongated growth as shown above this is often referred to as “witch’s broom.” Your rose will have more thorns; its buds, leaves and flowers will be distorted. The rose will be become more susceptible to mildew and black spot and generally die in two to five years. Younger, smaller roses die sooner than older more established roses, but they all die. This is fatal.

RRD Knock Out rose disease contain microscopic mites

Elongated Red Branches Contain Microscopic Mites

The Rose Rosette disease is a virus carried on the wind by a winglesss mite, the eriophyid mite. Mass plantings are generally all infected. There is no treatment. The rose will be infected in May though may not be symptomatic for a few months thereafter. The mites can survive a winter in the live canes and even in the roots. When you remove the foliage you remove the mites.

Because the virus is present in roots the rose really has no chance of survival. Remove the root ball of infected plants and destroy sprouts of any roots not eliminated if they develop because they will contain the virus as well.

Knock Out Rose Disease is a common name for Rose Rosette Disease. However, the cure suggested is to remove any infected plant completely. It contains the damaging mites. It has been noted that removing the damaged part of the plant often encourages the mites living within the plant to simply move lower.

The Pennsylvania nursery that introduced ‘Knockout’ roses has suggested that you prune the roses back by 2/3rds while they’re dormant in late winter to remove any overwintering mites and eggs in the bud crevices.

June Pocket Perennial Garden Canna Lillies and Day Lillies Early June Texas

June Pocket Perennial Garden: Knockout Roses, Cana Lilies, Day Lilies, Dusty Miller, Rose Rosette Disease can be seen in the rose on the left of the image with the “Witches Broom” in ruby red colors. Miscanthus Maiden Grass in the background.

Advancements in RRD Research

1. Identification of Resistance Loci

Researchers have identified quantitative trait loci (QTLs) associated with RRD resistance in both diploid and tetraploid rose populations. Notably, QTLs on linkage groups 5, 6, and 7 have been linked to reduced susceptibility, with some loci accounting for up to 40% of phenotypic variance in disease resistance.

2. Breeding Programs for Resistant Cultivars

Texas A&M AgriLife Research is leading initiatives to breed roses that are resistant to RRD and black spot disease. Their program integrates field evaluations, molecular markers, and genomic tools to develop sustainable rose cultivars. The goal is to produce roses that require fewer inputs and are resilient to both biotic and abiotic stresses.

This program has received substantial support from the U.S. Department of Agriculture’s (USDA) Specialty Crop Research Initiative (SCRI). For instance, in October 2022, a project titled “Developing Sustainable Rose Landscapes via Rose Rosette Disease Education, Socioeconomic Assessments, and Breeding RRD-Resistant Roses with Stable Black Spot Resistance” was awarded $4 million in USDA SCRI funding .

This initiative is led by Dr. David Byrne and Dr. Oscar Riera-Lizarazu at Texas A&M, in collaboration with researchers from multiple institutions, including the University of Minnesota, University of Tennessee, USDA-Agricultural Research Service, and others.

Regarding Department of Governmental and External Affairs (DOGE), there’s no publicly available information indicating that this department has impacted the rose breeding program. The program’s funding and progress is primarily influenced by USDA grants and collaborations with academic and industry partners.

3. Exploration of Alternative Hosts

Studies have expanded the known host range of RRD by demonstrating that the virus can infect various herbaceous plants, including tomato, pepper, cucumber, and spinach, under experimental conditions. This finding suggests potential alternative reservoirs for the virus, which could influence disease management strategies.