Tuesday, November 29, 2022

Trouble in the rose garden

Krista Middleton with son, Nolan, inspect roses in her front yard for signs of Rose Rosette Disease.
Krista Middleton with son, Nolan, inspect roses in her front yard for signs of Rose Rosette Disease.

5,000 year old Chinese notes indicate Asian gardeners cultivated wild roses about the time the first Egyptian pyramid was under construction.

As a matter of fact, give or take a millennia or two — right around the year zero — Far Easterners wiled away free time in huge parks of roses. Records indicate the Romans maintained rose nurseries in what is now southern Italy.

Still, the Caesars threw epic amounts of cold cash on fresh roses from the Egyptians who had obviously taken advantage of a great business opportunity. A dreamy painting of Cleopatra lounging on a bed of roses isn’t far fetched.

That “modern” rosebush you love today is one of about 5,000 genetic variations on the wild rose from geological yesteryear.

The interesting tidbit is that wild roses haven’t changed much in the last 40 million years. Eat your heart out Charles Darwin.

Wild roses have naturally hardy roots, and vigorously produce dainty apple blossom-like flowers once a year in the spring. We sigh over “modern” roses because they produce big, complex flowers again and again from spring to autumn. The caveat is their persnickety reputation in the hardiness and vigor departments. Just ask anyone who has grown one, or worse, grieved over one they lost.

The story goes this way. In the late 1800s a west coast rancher visited Japan, and saw wild Asian roses (rosa multiflora) used for many things like erosion control, ornamental plantings, wildlife shelters, and natural screens. A box of plants traveled to the U.S. where they performed above and beyond the call of duty because cattle refused to eat or walk through them.

What with birds spreading the seeds, and word of the horticultural bonanza, it wasn’t long before the “living fences” dotted The Land of The Free. State bureaucrats got into the action when they decided to beautify roadsides with the newcomers.

In 1941 an iceberg called Rose Rosette Disease (RRD) surfaced in the sea of descendants of the immigrant wild Asian roses. Thought to be biological salvation, the pestilence lived in a plant mite delivered hither and yon by wind. RRD itself appeared to ignore modern roses — until the breeding division of a company called Star Roses struck a genetic and economic motherlode with its no-maintenance, disease-resistant, modern Knock Out Rose. Drum roll please!

A completely false myth took the nation by storm: Knock Outs don’t need water, food or pruning. Wahoo! Ordinary gardeners’ fear and caution about roses evaporated overnight. Plants flew off nursery shelves. Nobody realized a second Titanic had launched from the Pennsylvania nursery company, but it became evident several years ago that Knock Outs have no resistance to RRD which, panicked plant scientists discovered, is a viral infection.

Nearly invisible carrot-shaped mites (eriophyidae as opposed to spider mites for those of you who care) chew rose leaf surfaces, and leave behind Rose Rosette Virus (RRV) which travels into the plant vascular system where it multiplies to cause cellular sickness from roots to flower buds.

The microbial delivery parasites over-winter in crevices of dormant rose twigs and bud scales then the infected females lay infected eggs in the same place the next spring. As one internet wag commented, RRV is the Superman rose’s kryptonite.

Now for the bad news. Early in this decade nobody thought RRD would become a big local problem. Steve Huddleston, the senior horticulturalist at the Fort Worth Botanic Gardens says he and his staff are currently fighting “an uphill battle” in the rose garden. RRD, he said, “is everywhere.”

Dallas Arboretum Vice President Dave Forehand called RRD an epidemic, and compared 2015 in North Texas to the epicenter of a horticultural earthquake. Victims of this scourge abound in southern Denton County.

“We’ve been hit by the currently incurable Rose Rosette on a few of our mature Knock Out Rose bushes. Only a matter of time before the others are affected,” said Lantana resident Kristine Hallingstad. “These looked healthy only three weeks ago but now have the telltale signs of this epidemic.”

So, you say, tell me in a nutshell what exactly is a virus? It is a non-bacterial pathogen composed of rogue pieces of DNA or RNA, the amino acid molecules that direct the action in the nuclei of live cells. It comes all wrapped up in a protein jacket that is sometimes also enveloped in a layer of fat for good measure. Is it a true cell? That’s undecided. The nasties float and hitchhike around in the biosphere until they bump into live cells with open doors. They can also stage an invasion.

In either case, once tucked inside, the virus makes babies. Naturally this intrusion sickens the host, maybe to death. If and when the virus nursery ruptures the whole organism is at risk. RRD infected rose canes sprout rosettes or thick clusters of soft breakable stems with long leaflets, hence the disease name. This abnormal growth is often referred to as a witch’s broom. Generally the so-called broom will be dark red, but on tea roses it may be the color of a lime.

Plants need to be green in order to photosynthesize food. A diseased cane may wear a bizarre-looking, thick coat of thorns unlike normal ones. Texas A&M Extension Service plant pathologists say symptoms may show up in as little as a few weeks to as much as several years after exposure.

In any case Rose Rosette Disease is always fatal to the plant. The gardener’s only recourse is to totally remove a sick plant then either burn it or seal the victim in a plastic bag, and send it off to the landfill. Remember RRD is systemic inside the shrub. That means the virus is in cells in the roots, canes, leaves, and flowering parts. Roots harbor remains of the virus, and left in the ground may re-sprout a new infected plant, or await contact with new rosebush roots. For how long is anybody’s guess. Viruses are tough little buggers.

What should a rose lover do? Remove and destroy offending plants, thoroughly police the soil to remove remaining scraps of root (yes, we now know the virus is also in the roots) then buy new stock only from rose suppliers known to be reputable. Always carefully inspect any rose before making a purchase, and save your receipts.

Give new plants plenty of space because on windless days the mites will leapfrog from one bush to another. Heavy winter pruning is a must.

What about mite sprays? These chemicals are aimed at spider mites. The rose rosette vector is a different creature. Horticultural oils, neem, insecticide soaps, and seaweed products applied to the outside of rosebushes are not systemic. They may kill the mites, but not the viral organisms coursing inside the plant.

Finally, consider following the Town of Flower Mound’s lead. Town spokesperson Molly Fox said the municipality is shying away from over-planting roses, and of course avoiding the use of Knock Out Roses.

“So far our stands of Knock Outs are well spaced and healthy,” she said.

She added that the community’s management discourages developers, builders and homeowners from using Knock Outs in landscaping.

“In our road medians we are using other plants, and focusing on Texas natives.”

Drive around the town, and you will see Texas Sage, salvia shrubs, and hollies which are Mother Nature’s tough guys.
Contact the writer at [email protected]

Noelle Hood
Noelle Hood
Noelle is our Resident Green Thumb and a Texas Agri-Life Master Gardener.

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