A bed of Knock Out Roses at Brooklyn Botanic Garden.

 

As long as you can develop tolerance and not demand total perfection, you can enjoy growing roses without knowing all the solutions to every rose diseases. As we get older, we just don’t have the energy to maintain a perfect disease free rose garden. As you will see in this article, I don’t recommend chemicals. Sanitation in the garden to me is the most important part of my rose gardening practice.

 

Blackspot is a fungal disease found most often on Hybrid Teas, Floribundas, and Grandfloras. Circular blackspots with feathery edge appear on leaves and stems, often surrounded by yellow patches.

Photo Credit – Missouri Botanic Garden

Control: Mulch right up to the canes to prevent spores from splashing on the rose leaves during heavy rain. Water the roots, but don’t wet the leaves of plants. Pick off infected leaves, remove any fallen leaves, and cut off infected stems. Prevent by spraying weekly and after rains with baking-soda solution of 1 tablespoon baking soda plus a tablespoon of light horticultural oil to 1 gallon of water.

 

Canker is a less troublesome fungal disease. Pruning cuts or wounds on stems provide an opening for germinating spores causing dark, swollen areas that can kill off a cane.

Photo Credit – extension.umn.edu

Control: The simplest treatment is not leaving stubs during normal pruning of susceptible roses and by ensuring that their canes are not chafing against each other or against any other objects like trellis or training ties. Also prune away and trash any infected canes.

 

Crown Gall is a very serious bacterial disease of roses. It is a hard, tumor-type growths that can occur at the crown, bud union or on the roots. It is caused by bacteria in the soil, and are more likely to occur on grafted than own-root roses by entering at the bud union.

Photo Credit – Missouri Botanic Garden

Control: Prevent by covering the soil around rose canes with a thick layer of soft mulch, like shredded bark, which prevents raindrops from splashing soil on canes, and be careful not to damage canes when planting. Once established, crown gall is incurable; remove and destroy the plant.

 

Powdery mildew first appears on young leaves where the leaves appear blistered or curled, with a haze of powdery white fungus and can spread to older leaves. Buds are also affected and many not open properly.

Photo Credit – gardeners’world.com

Control: Space and prune plants for good air circulation. Treatment is the same as with blackspot and can also be controlled by water washes at weekly intervals. Prune away and destroy all infected parts.

 

Rose Mosaic is the most commonly found virus in roses. The leaves appear to be wavy and have yellow lightening patterns, oak leaf patterns or simply gold to yellow veins. Plants infected with virus usually produce fewer good quality blooms. During the warm summer, typical symptoms can disappear only to come back as fall and cooler temperatures arrive.

Photo Credit – Missouri Botanic Garden

 Control: Since there is no cure for the virus disease, it is important to purchase only quality roses which has no symptoms of the disease. Just an added note, I had ‘Elina’ with rose mosaic. I was new to rose gardening at that time and was wondering while the leaves had a wavy pattern. Even then, I kept the plant for several years. I got some nice blooms and the disease never spread to the neighboring roses. I kept the plant and still in the garden when I sold my house.

 

Rose Rosette is a very serious rose disease and there is no cure so far. The foliage on the affected plant looks like witch’s broom, the leaflets looking distorted and wrinkled. It is believed to be caused by a virus carried from plant to plant by mites, or the reaction of the plant to substances injected by blister mites. It is rampant with Knock Out roses.

Photo Credit – Missouri Botanic Garden

Control: There is no known cure for the disease and once it is established in a plant, it could spread to other roses in your yard. You can lose your entire rose garden. Dig out the affected plant and discard it in the trash. Do not put it on the compost heap. I also don’t have any Knock Out roses. I dug them all up when I bought our townhouse.

 

Rust is easily identifiable rose disease. Raised dots of light orange or yellow can appear anywhere on the plant, but usually first show on the underside of leaves then spread on the upper sides of leaves. The spores are wind borne and germinate to infect the leaves. Spore germination requires cool summer temperatures and continuous moisture for at least two hours so the germ tubes can enter the leaf stomata.

Photo Credit – Flickr.com

Control: Infected leaves should be pruned in spring to prevent early season infections. Sanitation in the garden will reduce the spread of disease. Good air circulation by pruning dense growth will reduce the moisture level and prevent infection.

 

Until Next time. Stop and Smell the Roses.

Rosalinda