Roses Need to Be Disease-Resistant & Hardy for Missouri Life

Roses, the All-American flower, are noted for their beauty and fragrance. Unfortunately, in Missouri they are also noted for their pest problems, in particular the fungal disease blackspot (Diplocarpon rosae). If you’re willing to spray weekly with chemical fungicides or alternative organic control products, you can grow almost any rose successfully in Missouri. On the other hand, if you prefer to spend your time smelling the roses rather than spraying them, it pays to search out disease-resistant roses to grow, avoiding those with susceptibility to blackspot.

Many cultivars of roses are reportedly resistant to blackspot, but it’s easy to find conflicting information on this topic. Reasons may be that the disease affects plants differently in different climates, or that conditions weren’t right for the disease to develop that year. Without the combination of heat and humidity we get through the summer, a particular plant may not show symptoms of blackspot in, say, Michigan or Oregon, but would defoliate completely in Cape Girardeau. Or an isolated observation of no blackspot development may be a quirk of nature or lack of fungal spores in that particular garden.

This article will summarize results of several university studies on disease resistance in roses. The research was not conducted in Missouri, but should be considered reliable for the environment in which the roses were grown. In many cases the weather conditions are similar enough to Missouri’s that the results would be expected to be comparable here. In other cases, the results should only serve as a starting point to try roses that show promise elsewhere. Let’s start with the hot, humid conditions of Texas and Louisiana. Dr. Jerry Parsons of Texas A&M University, College Station, Texas, and Greg Grant, a former extension horticulture specialist who conducted his rose research at Baton Rouge, Louisiana, have come up with what they call "A Dozen Enduring Roses" for their region. During the test, 350 varieties of roses were left to grow without any intervention for disease or insect control. The "survivors" - those that still put on a good display of blooms and had little or no disease and insect problems are outlined below:
Climbers
‘New Dawn’ - a light pink flower; most disease resistant of the entire group.
‘America’ - a vigorous climber with fragrant orange flowers.
‘Don Juan’ - a red-flowered classic climber with glossy, leathery green foliage.
Pink Shrubs
‘Queen Elizabeth’ - a rebloomer that often shows up on recommended rose lists.
‘Belinda’s Dream’ - the plant form is that of a shrubby landscape rose, but blooms resemble hybrid tea roses.
‘Betty Prior’ - a vigorous pink rebloomer.
Yellow/Orange Shrubs
‘Apricot Nectar’ - a fragrant apricot-colored repeat bloomer.
‘Gold Medal’ - one of the few yellow roses with good disease resistance.
‘Fragrant Cloud’ - an orange rose so fragrant it won the American Rose Society’s Fragrance Award.
Red Shrubs
‘Chrysler Imperial’ - classic red rose with long stems suitable for cutting.
‘Mister Lincoln’ - popular traditional red hybrid tea rose.
White Shrubs
‘Double Delight’ - starts out creamy white but changes to strawberry red as it ages; has a spicy aroma that earned it an American Rose Society Fragrance Award.
‘Pristine’ - white blooms that shade to pink.

Next, we’ll move on to North Carolina where Richard Bir, extension horticulture specialist at the Mountain Crops Research and Extension Center in Fletcher, North Carolina, and Dr. Thomas Ranney from the Raleigh campus of North Carolina State University tested a dozen rose cultivars reportedly resistant to pests. Again, no spraying or fertilizing was done to any of the roses in the trial. Conditions at Fletcher are humid, but cooler than Missouri, since it is located in the Blue Ridge Mountains. During the study, seven of the 12 rose varieties showed no signs at all of blackspot or Cercospora leaf spot; three showed some signs of infection, but still looked good in the landscape; and two were nearly defoliated. Results are summarized below:
Complete Resistance
Rosa rugosa ‘Alba Semi-plena’ - pure white double flowers on a 4-foot tall shrub with dark green foliage; fall leaf color is yellow-orange.
Rosa rugosa ‘Blanc Double de Coubert’ - pure white semi-double to double flowers; plant tends to sucker; yellow fall color.
Rosa rugosa ‘Frau Dagmar Hastrup’ a.k.a. ‘Frau Dagmar Hartopp’ - abundant single pink flowers all season long; red hips are showy by midsummer; dark green foliage turns yellow-orange in fall; neat mounding 3 1/2-foot tall plant.
Rosa rugosa ‘Roseraie de l’Hay’ - pink fully double fragrant flowers in clusters in June, then sporadically the rest of the season; did suffer some Botrytis (gray mold) on blooms in wet weather.
Rosa rugosa ‘Alba’ - 4-inch diameter white blooms; showy orange-red hips by midsummer; dark green foliage turns yellow in fall.
‘Sarah Van Fleet’ - a hybrid rose with double, rose-pink fragrant blooms suitable for cutting; sprawling open growth habit.
Rosa rugosa ‘Topaz Jewel’ - 4-inch semi-double light yellow flowers with repeat bloom; dark green foliage.
Good Resistance
Bonica™ (‘Meidomonac’) - pink reblooming shrub rose with heaviest flowering in spring; first shrub rose to win All-America Rose Selection status; produces orange-red hips.
Alba Meideland® (‘Meiflopan’) - small, double white flowers from June through fall; low growing, spreading plant, up to 12 feet wide.
Scarlet Meideland® (‘Meikrotal’) - double scarlet flowers in early summer, then sporadically through fall; spreading plant 2 1/2 feet tall by 10 feet wide.

Our final stop is at the University of Wisconsin in Madison, Wisconsin, where Jeffrey Epping and Dr. Ed Hasselkus examined the hardiness and disease resistance of many shrub roses. Admittedly, Wisconsin is a lot cooler than Missouri, but some of their recommended varieties show up on the previous lists, so their recommendations are certainly a good place to start with your own trials of disease resistant roses for your own backyard. Their results:
Recommended Rugosa Roses
Rosa rugosa ‘Albo-plena’ - perhaps the same as ‘Albo- semi-plena’ above?
Rosa rugosa ‘Belle Poitevine’ - slightly fragrant, semi- double mauve-pink flowers; yellow to orange fall foliage color; 3 1/2 - 4 feet tall.
Rosa rugosa ‘Blanc Double de Coubert’ - see above.
Rosa rugosa ‘Frau Dagmar Hastrup’ - see above.
R. X calocarpa - a hybrid with R. rugosa with purplish crimson fragrant flowers; foliage turns burnt orange/red/ maroon in fall; attractive orange-red hips.
Acceptable Rugosa Roses
Rosa rugosa ‘Hansa’ - semi-double purplish red fragrant flowers; many orange-red hips; yellow to orange fall foliage color; leggy habit.
Rosa rugosa ‘Scabrosa’ - single deep mauve-pink flowers; large orange-red hips; yellow to orange fall color.
Rosa rugosa ‘Therese Bugnet’ - double, medium pink very fragrant flowers; blue-green foliage turns yellow and orange in fall; suckering habit creates a thicket; very attractive shiny red canes in winter; susceptible to rose girdler.
Rosa rugosa ‘Roseraie de l’Hay’ - see above.
Rosa rugosa ‘Topaz Jewel’ - see above.
Other Disease Resistant Shrub Roses
Bonica™ (‘Meidomanac’) - see above.
Carefree Beauty™ (‘Bucbi’) - large, semi-double medium pink blooms from June until frost; upright, open growth habit.
Rosa hugonis - single bright yellow blooms with very fine-textured foliage; yellow to maroon fall color; very thorny canes 6 to 8 feet tall.
Rosa spinosissima altaica (Rosa pimpinellifolia altaica) - single pale yellow to white flowers; small brownish-red hips; suckering habit 3 to 4 feet tall suitable as a groundcover.
Rosa setigera - single pale pink blooms; abundant, persistent small red hips; orange to maroon fall color; sprawling canes 12 to 15 feet long.
Rosa virginiana - single light pink blooms; bright red hips persist through winter; orange to maroon fall color; red glossy canes 3 to 5 feet tall are showy in winter. (Denny Schrock, Extension Horticulture, UMC)