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Tag: rose

Rose Rosette Virus Active in Summer 2023

Posted on by Teresa Roberts

By Judy O’Mara, Director, K-State Plant Disease Diagnostic Lab

 

Rose rosette is currently showing up in Kansas gardens. This disease is a serious problem in wild multiflora roses but also goes to many common garden roses.

The rose rosette virus is spread from plant to plant by a microscopic eriophyid mite (Phyllocoptes fructiphilus).  It is the only known insect vector of the rose rosette disease. The mite can be wind dispersed or moved around on tools, clothing or infected plant material. Mites can successfully overwinter on the rose plant. The rose rosette virus can also be spread through grafting.

Rose rosette causes a progressive deformity of the rose plant that gets worse over time. It is challenging to identify visually because symptoms vary widely from plant to plant. Some prominent symptoms can include reddish or distorted leaves, stems that are elongated and thickened, a proliferation of shoots (rosette), and excessive thorniness. Plants infected with rose rosette are also more susceptible to winter damage.

An initial symptom of rose rosette might be an elongated stem with reddish leaves that stands out above the normal growth habit of the shrub. Reddish leaves are a tricky symptom because roses put out new flushes of growth throughout the growing season and the new leaves commonly start out red and then green up.

More characteristic for rose rosette virus are symptoms of bunchy growth or a proliferation of shoots. This symptom is referred to as a rosette or witches’ broom.  Some roses have a bunchy growth pattern so keep in mind that this symptom development should look new or different from the established growth habit of the plant.

A striking symptom for rose rosette is excessive thorniness along the stems. These thorns are generally small, green and soft whereas normal thorns tend to be larger, hard and sharp. Infected plants usually have both types of thorns present.

Pruning out symptomatic portions of infected rose plants will not eliminate the disease.

Plants with rose rosette can survive for one to two years but the virus will continue to spread within a planting. It is important to remove infected plants as soon as possible, including the roots. Infected  plants should be placed in trash bags to reduce further spread of the eriophyid mites.

Interspersing roses with non-rose hosts can slow down the spread of the mite and the rose rosette disease. Dead heading roses throughout the growing season will help minimize the habitat of the eriophyid mite. Resistance is not available for commonly grown garden roses. Native roses resistant to rose rosette include: prickly rose (Rosa acicularis ), prairie rose (Rosa arkansana), smooth rose (Rosa blanda), swamp rose (Rosa paulustris), Carolina rose (Rosa carolina), and scotch rose (Rosa spinosissima).

Visual identification of rose rosette virus disease can be challenging. The K-State Plant Disease Diagnostic Lab does offer a PCR test that can confirm the presence of rose rosette virus.  Testing can be expensive but might be worthwhile in locations with large plantings of roses.

 

K-State Plant Disease Diagnostic Lab

4032 Throckmorton PSC
1712 Claflin Road
Manhattan, KS 66506
clinic@ksu.edu
785-532-6176

 

Useful references:

Rose Rosette Disease: A Diagnostic Guide. N. Claros, etal. https://apsjournals.apsnet.org/doi/10.1094/PHP-05-22-0047-DG

Rose Rosette Disease. J. Olson, etal.
https://extension.okstate.edu/fact-sheets/rose-rosette-disease.html#management-guidelines-for-rrd

Feeding Damage to Rose Leaves

Posted on by Teresa Roberts

From the KSU Entomology Newsletter, article by Raymond Cloyd

We have received numerous inquiries regarding insects feeding on the leaves of rose plants. The insects are sawflies and there are at least two species that attack roses this time of year: the rose slug, Endelomyia aethiops, and the bristly rose slug, Cladius difformis. Rose sawflies are the immature or larval stage, which eventually become a black to yellow adult that resemble wasps. Rose sawfly females create openings or slits along the edges of rose leaves with their saw-like egg laying device (ovipositor) in which eggs are inserted. Larvae emerge (eclose) from the eggs and resemble small slugs. Larvae are approximately 1/2 of an inch long when full-grown and yellow-green, with an orange head.

The larvae will fall onto the soil surface to pupate. Rose sawflies overwinter as pupae in earthen cells created by the larvae. There is typically one generation per year in Kansas. Rose sawfly larvae cause damage by feeding on the underside of rose leaves causing the leaves to appear skeletonized.

 

 

 

Small infestations of rose sawflies are best dealt with by removing the larvae by hand and placing into a container of soapy water. A high pressure water spray will quickly dislodge sawfly larvae from rose plants. Once dislodged the larvae will not crawl back onto rose plants. There are contact insecticides containing various active ingredients that are effective in managing populations of sawflies. Sawflies are not caterpillars.

Consequently, the bacterium, Bacillus thuringiensis subsp. kurstaki, which is the active ingredient in various products (e.g. Dipel®) has no activity on sawflies because the insecticide is only effective against caterpillars.

Rose black spot

Posted on by kennelly

Hey, what are those black spots on those roses?

IMG_4003

You might have guessed, it’s “black spot.”

Here is some great information from Ward Upham:

Blackspot of Roses  
    A common disease of roses is blackspot, a fungus disease that can cause defoliation of susceptible plants. Look for dark, circular lesions with feathery edges on the top surface of the leaves and raised purple spots on young canes. Infected leaves will often yellow between spots and eventually drop.
    The infection usually starts on the lower leaves and works its way up the plant.  Blackspot is most severe under conditions of high relative humidity (>85%), warm temperatures (75 to 85 degrees F) and six or more hours of leaf wetness. Newly expanding leaves are most vulnerable to infection. The fungus can survive on fallen leaves or canes and is disseminated primarily by splashing water.
    Cultural practices are the first line of defense.
    1. Don’t plant susceptible roses unless you are willing to use fungicide sprays. For a list
of blackspot resistant varieties, go to: http://www.ppdl.purdue.edu/ppdl/weeklypics/3-22-04.html
    2. Keep irrigation water off the foliage. Drip irrigation works well with roses.
    3. Plant roses in sun in areas with good air movement to limit the amount of time the
foliage is wet.
    4. Remove diseased leaves that have fallen and prune out infected rose canes to minimize inoculum.
    If needed, protect foliage with a regular spray program (10- to 14-day schedule) ) of effective fungicides. Recommended fungicides include tebuconazole (Bayer Disease Control for Roses,Flowers and Shrubs), myclobutanil (Immunox, Immunox Plus), triticonazole (Ortho Rose & Flower Disease Control) and chlorothalonil (Broad Spectrum Fungicide, Garden Disease Control, others).

Here is a closer zoom of some of the spots.

IMG_3999

If you really look closely (or, in real-life, use a hand-lens) you might see tiny little bumps. Those bumps are the structures where the fungus produces its spores. Zooming in closer, with the help of a compound microscope, we can see the individual spores. Each spore can cause a new infection.

black-spot-spores-2