Help Us Keep A Watch Out for Rose Rosette Disease

Help Us Keep A Watch Out for Rose Rosette Disease

Austin N. Fife, PhD student, Entomology

University of Florida IFAS

North Florida Research and Extension Center

Phyllocoptes fructiphilus: a new threat for Florida roses

Figure 1: Phyllocoptes fructiphilus . Image Credit Austin N. Fife, UF / IFAS

Phyllocoptes fructiphilus Kefier is a microscopic plant-feeding arachnid belonging to a group of spindle-shaped mites known as Eriophyoid mites. Eriophyoid mites are second only to spider mites in their economic importance and potential for plant damage: some species create galls, others deform plants with their feeding activity, and a few species are capable of spreading viruses. Fortunately, eriophyoid mites very host specific and P. fructiphilus only feeds on plants in the genus Rosa, which includes all of the true roses which we are familiar with.

P. fructiphilus does not cause damage by its feeding alone, but is a pest due to its relationship as the vector of an emaravirus: Rose rosette virus (RRV). RRV infection creates Rose Rosette Disease (RRD), with the following symptoms: witches’ brooms/rosetting, deformed flowers, increased prickle density, elongated shoots, reddened leaves and stems, and increased die-back which ultimately kills the rose host. RRD is the most serious disease of roses, creating millions of dollars of losses for growers. Rose Rosette Disease and the mite have invaded the southeastern United States as the non-native Rosa multiflora (Thunb) has spread invasively towards the eastern coast and by the introduction of infected roses from out of state into Florida.

Figure 2: EDDMapS. 2020. Early Detection & Distribution Mapping System. The University of Georgia – Center for Invasive Species and Ecosystem Health. Available online at http://www.eddmaps.org/

RRD was initially detected in Florida in 2014 on 15 plants; however, the plants were destroyed and P. fructiphilus were not detected on the roses after that time.

In early 2019, a survey of predatory mites on roses found eriphyoid mites in samples obtained while surveying roses in Leon County, Florida. The mites were sent to the Florida Department of Agriculture and Consumer Services – Department of Plant Industry (FDACS-DPI) and were all identified as P. fructiphilus by Dr. Sam Bolton. To date, none of these roses have shown signs or symptoms of RDD and none of these plants have tested positive for presence of the virus.

Figure 3: Black dots indicate individual sites which have been surveyed for Phyllocoptes fructiphilus. Orange dots indicate a number of sites with populations of P. fructiphilus detected in Leon county, Florida. No symptoms of Rose Rosette Disease have been seen on these plants to date. Image Credit Austin N. Fife, UF / IFAS

This is the first recorded instance of P. fructiphilus in Florida and is worrisome despite the absence of the virus. Fortunately, RRV is currently not established in Florida. However, the presence of P. fructiphilus, along with past detections of RRV in Florida warrants an increase in monitoring efforts for the mite and virus in Florida.

Figure 4: Typical symptoms of Rose Rosette Disease. Image Credit Austin N. Fife, UF / IFAS

How can I identify roses that have Rose Rosette Disease?

It is difficult to identify the symptoms of RRD in the field for a few reasons. Primarily, there are different growth habits for different rose cultivars. What appears to be ‘excessive thorniness’ in one cultivar may be normal for another, and is can be easy to mistake the redness of new flush with symptoms of the RRD. In addition, glyphosate damage from improper use of Roundup or similar products can have a very similar appearance to diseased roses. The best way to verify RRD infection is to use molecular testing for the virus. Identifying the presences of eriophyoid mites is useful for diagnosis, but they are too small to see with pocket loupes and are difficult to find unless there are large numbers of mites. To properly identify an eriophyoid mite as P. fructiphilus requires the use of a compound microscope with a specially prepared microscope slide of the mite, as well as reference materials and a trained individual who knows what characters to look for.

What to do if I suspect that my roses are infected with Rose Rosette Disease?

We recommend reporting suspected cases of RRD to your local extension agency or the Florida Department of Agriculture.

Where should I send my samples?

Plant Disease Diagnostic Clinic at the North Florida Research and Education Center in Quincy: https://nfrec.ifas.ufl.edu/plant-pathology-clinic/

Mathews Paret, Director, Plant Disease Diagnostic Clinic – UF NFREC (850) 875-7154, paret@ufl.edu

UF/IFAS Disease Diagnostic Center in Gainesville:

  • 392-1795, pdc@ifas.ufl.edu

2570 Hull Rd Gainesville, FL 32603

Florida Department of Agriculture and Consumer Services – Division of Plant Industry

1-888-397-1517 Helpline (352) 395-4600 (Helpline Number, Outside of the United States) DPIHelpline@FDACS.gov

The Doyle Conner Building 1911 SW 34th St. Gainesville, FL 32608

Figure 5: Phyllocoptes fructiphilus is a refuge-seeking mite ,which hides under rose sepals, which are covered in tiny glandular plant hairs known as trichomes that protect the mites. Image Credit: Austin N. Fife, UF / IFAS

How Can I Manage Rose Rosette Disease?

Currently, there are no commercially available rose cultivars known to resist Rose Rosette Disease or Phyllocoptes fructiphilus. A major difficulty lies in the cryptic nature of these mites, which hide underneath the rose sepals. It is important to consider this when considering which control methods to use. Methods which require direct contact with the mites to kill them are unlikely to work.

This makes it difficult for chemical applications which require contact with the pest to work.

Keeping that in mind, there are a few things you can do to reduce your risk of RRD and prevent the spread of the mite:

  • Eliminate infected wild roses nearby
  • Heavy pruning followed by horticultural oil spray may reduce populations of the mite, but cannot prevent a viral infection from spreading.
  • Space plants so their leaves and roots don’t touch
  • Dispose of diseased roses properly: bag up infected materials and dispose of in areas away from other roses
  • After removing infected plants, spray remaining plants with miticides recommended at https://roserosette.org/control/
  • Spray uninfected plants adjacent to removed (infected) plants

 

Unique Roses for Northwest Florida and Beyond

Unique Roses for Northwest Florida and Beyond

Monsieur Tillier – Tea rose from the late 1800s.  A good choice where a large, free-flowering shrub is needed – Image Credit Matthew Orwat

Home Gardeners, when they think of roses, their mind inevitably turns to the ‘Knockout’ rose and its offspring. That’s fine, there’s nothing wrong with ‘Knockout’ roses, it makes a great ornamental landscape plant, and it’s easy to propagate.

With all the ‘Knockout’ mania, since the early 2000s, many garden roses, that are well adapted to the Northwest Florida climate, have been left out of the home garden to a large degree.

Several roses, which were grown in Florida commonly in the last hundred years, and recommended by former University of Florida president H. H. Hume in his book “Gardening in the Lower South,” are still grown here today. To obtain these roses gardeners must look to small nurseries scattered throughout central Florida and Alabama, or order them from larger nurseries in Texas where the “Texas A&M Earthkind Rose Program” has taken off.

 

Below are a few examples of easy to grow roses, that are just as disease resistant as the ‘Knockout,’ but offer more variety in color and form that home gardeners might enjoy as much as or more than ‘Knockout’. They have been grown successfully throughout southern Texas for over 30 years, and at the Washington County Extension Office for the past seven years without spraying fungicides or insecticides. Several of these cultivars were also involved in a 3-year rose trial at the UF/IFAS North Florida Research and Education Center, in Quincy.

One caveat I have regarding these roses is that disease resistance is lessened when irrigated with overhead irrigation. Even the most disease resistant roses will develop issues if leaves are constantly left wet.

Belinda’s Dream makes a moderately sized shrub and produces large flowers, especially in the spring and fall. Image Credit – Matthew Orwat

‘Belinda’s Dream’

‘Belinda’s Dream‘ was bred by Texas A&M Professor Robert Basye in 1988, as a culmination of years of intense breeding and selection for disease resistant landscape and cut flower roses. It makes a 4-5 foot shrub that grows about 3 feet wide. Apple-green foliage clothe its pleasing shrub form. It’s free flowering but not overly vigorous, so it’s easy to keep in bounds.  Disease resistance is high, there’s rarely any blackspot of note, under no-spray conditions, and only slight powdery mildew in a few years when conditions are favorable for fungus development.

In cool spring or fall conditions, the clear pink flowers can top six inches in diameter, and contain over 200 petals, but regular hot conditions during the summer usually reduce flower size to four inches. This rose loves to be part of mass plantings, particularly when planted 3 feet apart in a triangular formation. It has a reputation as being moderately easy to propagate.

Rosette Delizy is very colorful and disease resistant. A great addition where a spot of color is needed – Image Credit Matthew Orwat

‘Rosette Delizy’

 

‘Rosette Delizy‘ is a French Tea rose that was introduced to the U.S. nursery trade in the mid-1920s. Since it was bred before the days of modern fungicides, it sports excellent resistance to disease. It shows no powdery mildew, and only the occasional leaf with blackspot under no-spray conditions.

This is strictly a rose for the coastal south, since it does not like cold temperatures, and cannot thrive north of zone 7b without protection.

Color is striking, opening yellow with petal edges changing to pink as the flowers age. Cooler weather brings out deeper russet and maroon tones. It has a light “tea” fragrance. This mannerly shrub gets 4-5 feet tall and 3-4 feet wide. It requires very light pruning, and can actually be killed from heavy-handed gardeners with shears in hand. Minor flaws noted in this rose are that it is somewhat sparsely foliated, and somewhat difficult to propagate.

 

Madame Antoine Mari – The perfect buttonhole rose produces flowers with delicate, soft colors perfect for arranging. This rose is a mannerly grower suitable for smaller landscapes. Image Credit Matthew Orwat

‘Madame Antoine Mari’

‘Madame Antione Mari’, a Tea rose, was introduced in 1900 when the buttonhole rose was all the rage. Massive quantities of perfectly formed delicate buds of pink and ivory quickly open into 3 inch flowers that decorate the bush like butterflies fluttering in the wind. Re-bloom is fast. Additional interest in the landscape is created by the deep red color of new foliage.

This makes a mannerly shrub for the small landscape, easily kept at 3-4 feet tall, and 5-6 feet wide by light pruning. Disease resistance is above average in a no-spray garden, with very low blackspot infection rates, and only occasional powdery mildew. This rose has been found to be easily propagated with the author reaching near 100% success rate.

 

Mrs. B. R. Cant at the Quincy rose trial in 2013.

‘Mrs. B. R. Cant’

 

No mention of easy to grow roses is complete without the mention of ‘Mrs. B. R. Cant’. In the trials UF/IFAS horticulturists performed at Quincy and Plant City, this variety was rated the best performer. It has been in continuous cultivation since 1901, and is often found at old home sites and gardens in Washington County.

This makes a large garden rose, easily topping 8 feet in height, and just as wide.  Deep pink flowers are borne profusely from March to first frost. Disease resistance is outstanding, and it’s easy to propagate. Plants are densely clothed in medium green leaves. This rose is often grown in hedges as a substitute for a fence. One of the best all-around garden roses for the gulf south.

 

Nursery Availability

I provide presentations at workshops on these roses multiple times a year, throughout the Florida Panhandle. The recurring question I get is, “Where are these roses available locally?”  Hopefully this article will inspire some local gardeners to try these easy to grow roses, and others, since these are just a few of the roses available that do very well in North Florida under no spray conditions. If you are interested in more information, contact, Matthew Orwat at UF/IFAS Extension Washington County.

Be on the Lookout for Rose Crown Gall

Be on the Lookout for Rose Crown Gall

Crown gall symptoms on roses caused by the bacterium Agrobacterium tumefaciens (Rhizobium radiobacter) – Photo credits: Kamil Duman

A plant with a mature gall that is potentially releasing the crown gall bacterium into the potting media. Photo credits: Susannah Wright

For gardeners, rose enthusiasts and rosarians, each of the many rose diseases is as important as the others. But we can say for sure Crown Gall is one of the most unsightly of the many rose diseases that can been seen currently.

The disease got this name from the large tumor-like swellings (galls) that typically occur at the crown of the plant, just above the soil level. The cause of crown gall disease is a bacterium that resides in the soil, Agrobacterium tumefaciens (updated scientific name Rhizobium radiobacter).

SYMPTOMS

Galls or overgrowth (1/4 inch to several inches in diameter) of host plant tissue typically form at the soil line but also can form on branches or roots. Galls are initially white, spherical, and soft but darken with age as outer cells die. It can either be almost entirely on the surface of the plant and easily detached or can be almost indistinguishable from normal plant tissue except for its greatly enlarged appearance.

The bacterium that causes Crown Gall disease survives and persists in the soil for up to 3 years. It can invade recent wounds on the branches or roots. Swelling can be seen as early as 14 days following entry of the bacterium into the plant. The tissue near the gall can be crushed due to rapid cell enlargement. If vascular tissue is crushed, wilting can result from the restricted water movement.

 

Early stage symptom of Crown Gall on roses can be noticed as the small white galls. Photo credits: Susannah Wright

The galls can enlarge to a quarter size in a short period of time from the initial small galls. Photo credits: Mathews Paret

ABOUT THE BACTERIUM

Agrobacterium uses its genes as a weapon to attack plants. It enters the plant mostly from the soil through wounds on the roots or lower stem or from the branches during plant pruning. Symptoms are caused by the insertion of a small segment of DNA (known as the T-DNA), from a plasmid, into the host plant cell, which is incorporated into the plant genome. When the plasmid links up with the plants own DNA, the altered plant cells start dividing rapidly and uncontrollably, and the root or stem develops a tumor-like swelling.

Galls can range from pea size to softball size. Tiny cracks from freezing temperatures or wound sites can be the site of gall formation. Once the wound compounds are generated, the bacteria detach from the xylem cell walls and are carried upward with water during evapotranspiration to the wound site where they initiate galls. One of the common ways of the spread of the disease is by pruning infected plants and moving the bacterium accidentally while pruning nearby healthy plants.

The crown gall bacterium is a soil pathogen, which means main inoculum source is soil. The bacterium can overwinter in infested soils, where it can live as a saprophyte for several years. The bacterium can easily during field preparation, pruning and irrigation. Insects, nematodes and grafting materials, can also transfer the bacterium.

The galls will turn dark in color as they age. Photo credits: Kamil Duman

 

HOW CAN YOU MANAGE ROSE CROWN GALL DISEASE

  • Plant only disease-free roses. Check very carefully before you buy plants for any kind of galls in the crown or branches. Use good sanitation practices in handling roses.
  • Plant in clean soil. Avoid areas with a history of crown gall infestation.
  • Avoid fields with heavy infestations of root-attacking insects and nematodes.
  • Select well-drained soil and irrigate from clean water sources.
  • Keep grafts and buds well above the soil line.
  • Destroy diseased plants as soon as you notice them to avoid cross-contaminating other plants, or pruning equipment. Also, do not keep infected plants with healthy plants, as the likelihood of accidental transmission through pruning is high.
  • Avoid mechanical injury to plants from tillage and hoeing. Provide winter protection so that the bark does not crack.
  • Disinfect pruning tools between plants. disinfect budding/grafting tools before and after use. Bleach (10%; equivalent to 0.6% sodium hypochlorite), or quaternary ammonium-based sanitizer are effective as disinfectants. Make sure to prepare fresh stock routinely.
  • If crown gall plants are noted, please let your local county extension agent know about it and they will be able to contact us for additional site-specific management plans if needed.

Gall formation at pruning sites indicating contamination of the plant during pruning. Photo credits: Kamil Duman

 

 

Authors: Kamil Duman, Susannah Wright, Fanny Iriarte, Barron Riddle, Gary Knox and Mathews Paret, University of Florida – NFREC, Quincy, FL

 

 

Northwest Florida Rose Symposium Saturday September 16, 2017

Northwest Florida Rose Symposium Saturday September 16, 2017

On Saturday, September 16th, 2017, from 9AM to 12PM, UF / IFAS Extension Washington County will be providing a rose gardening workshop for gardeners across the Panhandle. Many roses are hard to grow in the Florida Panhandle without investing considerable time and energy into spraying for insect and disease problems. This workshop will teach attendees how to select and sustainably grow roses adapted to the hot-humid conditions of the Southern Gulf Coast. There will be opportunities for outdoor learning and hands-on activities. 

Topics include:

  • Selection of disease resistant rose cultivars adapted to the lower South
  • Resources to obtain hard to find easy care rose cultivars
  • Soil and Nutrient Management
  • Disease and insect management
  • Irrigation
  • Rose Propagation

Participants will be given the opportunity to propagate their own rose and take home their own propagation assembly to grow their own roses from scratch.

Refreshments will be provided and a door prize will be available.

Address: Washington County Ag Center Auditorium, 1424 Jackson Ave, Chipley FL 32428.

Pre Registration required for count: Contact Nikki or Cynthia at 850-638-6180 or email Matthew Orwat at mjorwat@ufl.edu

or register online at eventbrite HERE !

 

Workshop on New and Re-emerging Rose Diseases and Pests, July 11, 1-5 pm.

Workshop on New and Re-emerging Rose Diseases and Pests, July 11, 1-5 pm.

Come to this free workshop to learn about the latest results of University of Florida and national research on roses. Receive hands-on training on symptoms and management of rose rosette disease, rose mosaic disease, crown gall, and rose pests.

 

FL Pesticide CEUs, FNGLA CEUs and GA Pesticide CEUs have been applied for!

 

This program is geared for nursery and greenhouse growers, landscapers, municipal maintenance personnel, Extension personnel, Rosarians, rose enthusiasts and science teachers. Sponsored by Farm Credit of Northwest Florida and Harrell’s.

 

To register for this FREE event, please go to: https://rose-diseases-pests.eventbrite.com