GARDENPlants and seeds

How To Care For Garden Roses

A rose problem is almost always a reflection of the plant’s environment. Bad drainage, too little water, poor soil preparation, insects, disease – all are environmental conditions that can either be remedied or prevented from the start. This leaflet is to help you diagnose and treat problems. Plant problems can be caused by either living organisms (insect, fungal, or bacterial pests) or non-living cultural conditions. If the damage is uniform it is usually a non-living cause, while living pathogens cause non-uniform damage. 

The first line of defense against any rose problem is a strong, healthy plant. A little advance preparation such as the addition of wellcomposted organic material to the soil before planting, will provide the optimal blooming environment. Fertilizer, amendments, and pruning helps as well. We have collected a list of common rose problems in the backyard garden along with suggested remedies. We have endeavored to recommend the best and most effective remedies. Please follow label directions on all pesticides to avoid plant damage.

Plant roses in late February; early March in coastal areas. Spring rains will promote and spread blackspot. Cleanup of plant debris is a must. Winter lime-sulfur sprays of dormant plants will help stop blackspot before it begins. Powdery mildew is a problem in mid-season. To help prevent it, plant in an area where there’s good air circulation and avoid wetting rose foliage. Prune annually in December and January. Cut back about half the height of the plant. Irrigation is a paramount concern when planting a rose garden. Growing in hot, dry summers is not difficult with efficient watering and fertilizing techniques. Mulching helps cool roots and retain moisture. Roses are America’s favorite flower. They are easy to grow and provide abundant blooms when properly cared for. Below is a quick list of plant problems that can occur in the rose garden. You will see that they are grouped into insect, disease, and cultural categories. 

-INSECT PROBLEMS

Symptom: Masses of bugs on the buds and leaves. 
Cause: Aphids- green, red, or black soft bugs, about 1/8″ long, found clustered mostly on new growth. They appear in spring and can remain all summer. 
Remedy: Most insecticidal sprays, including insecticidal soap, are effective. Aerosol insecticides labeled for plant pests will also work: spray up-wind and allow the mist to drift through the plant. Or simply hose off the insects when you water. 

Symptom: Blooms are shredded, discolored or buds distorted. 
Cause: Thrips – light brown insects, very slender, about 1/8″ long. Squeeze an open bloom and watch the inside of the petals for movement. Thrips move quickly. They are spread by wind. 
Remedy: Apply systemic containing acephate or disulforon when 1″ or more of new growth has occurred in spring. Contact treatments of pyrethrins, pyrethroids or other pesticide types can be used on a rotational basis when buds are peasized. 

Symptom: Leaves stuck together, unopened buds with holes bored into them 
Cause: Omnivorous leaf roller- a moth larvae that makes a cocoon like structure with leaves. 
Remedy: Use B.T. (Bacillus thuringiensis) or systemics as previously explained for thrips. 

Symptom: Leaves appear fuzzy yellow on surface; underside has small red specks, webbing or spider-like insects moving about. (Best seen with a magnifying glass.) 
Cause: Spider-mite (red spider or 2-spotted mite). Microscopic in size, but visible to the naked eye. Hot weather is prime spider-mite season. Activity increases or decreases with temperature changes. 
Remedy: Apply insecticidal soap, spray oils, miticides or high pressure hose water. All treatments must be applied to the underside of leaves in order to come in contact with the mites. 

Symptom: Leaves have been eaten leaving either skeleton structure or mid-ribs. Unopened flower buds chewed and open buds damaged. 
Cause: Beetles – most notorious is the Japanese beetle, metallic brown with a green head. (Caterpillars can also cause the same symptoms.) 
Remedy: Sprays, dust and “shaking.” Sprays of Carbaryl (Sevin) or Rotenone are somewhat effective. Apply Bp (Bacillus papilliae) or ‘milky spore’ when the problem is first detected in spring or late summer. Neem oil, a new natural insecticide, or its derivative Azadirachtin, has shown some limited control. A practical, yet effective approach is to spread cloth or plastic on the ground and shake the beetles off the plants. Traps can be effective if placed away from your roses. 

Symptom: Drooping unopened buds, accompanied by a small discolored stem slightly below the bud. 
Cause: Rose Midge – a small fly that pupates in the ground below the bush, then flies up and lays eggs in the soft upper stem. The hatched larvae eat the stems and cause breakage. The worm then drops to the ground to complete the last stage of metamorphosis into a fly. 
Remedy: Spread systemic granules on the ground below the bush to control this pest. Sprays are of limited value here because of midge life stages in the ground. 

Symptom: Holes in pruned cane ends. Circular pieces cut from leaf margins. 
Cause: Leaf cutter bees – they use the circular leaf pieces for egg partitions inside the burrowed cane. 
Remedy: Controlled by applying white glue to the can ends. NOTE: Leaf cutter bee is a beneficial, effective garden pollinator. Our suggested damage prevention measure is preferable to eradication. 

- DISEASE PROBLEMS –

Symptom: Tumor-like growths on canes, roots or at bud union. 
Cause: Gall (aerial, crown, or root) – a bacterial problem entering through a wound or contaminates pruning tool. 
Remedy: Prune away affected section, if possible. (Galls on the graft would kill the plant if pruned off.) Be sure to sterilize pruners and other tools with bleach or alcohol to prevent bacteria from spreading. Destroy seriously weakened plants. Treat soil with bactericide or leave fallow for two or more seasons before replanting. 

Symptom: Leaves fold at mid-rid, or are distorted. White powdery material appears on the forming buds and leaf tops or undersides.
Cause: Powdery Mildew – a fungal disease fostered by cool nights, warm days, and high humidity. 
Remedy: Spray Triforine or myclobuanil (Immunox), dust with sulphur, or spray with baking soda and soap. Make sure plants have good air circulation and ample sunlight. 

Symptom: Dark irregular splotches on the leaves, dropping of healthy leaves, yellowed leaf sections. 
Cause: Downy Mildew – this systemic fungus disease is present in the soil and will begin to cause problems when night temperatures reach 55F to 65F, with still air measuring 85% humidity. 
Remedy: Cut back the defoliated plant. Clean up debris, dust with sulfur and spray with Aluminum tris (Aliethe). 

Symptom: Brown spots on petals, also red-pink spots on lighter colored flower buds. Brown dieback of cut canes; brown fuzzy mold on debris around the plant. In severe cases, the entire flower bud rots. 
Cause: Botrytis blight – high-humidity nights or rainy cool periods favor fungus growth. 
Remedy: Spray with fungicide. Remove all damaged twigs on the plant, and clean up leaves and debris below to prevent fungus from spreading. Maintain good air circulation. 

Symptom: Dark black spots on the leaves. The spots tend to be round, varying in size from pinpoint to quarter sized. Half of leaf yellows or leaf drops completely from the plant. 
Cause: Black spot – this is a fungus favored by rainy weather or improper watering. 
Remedy: Sprays-Dusts-Watering Technique. Begin in winter with a dormant lime-sulfur spray. Remove dropped leaves and other debris. Spray with Neem oil, Trifoine, Mtclobutanil, or a sulfur-based fungicide on a rotational basis. Fungus spores are found on leaf undersides so spray upward from underneath. When watering, keep foliage dry or water in the morning so foliage dries by midday. 

- CULTURAL PROBLEMS –

Symptom: Slow starting roses. 
Cause: Dry canes, dry roots. 
Remedy: Water the roses heavily during the first three weeks. Spray canes during the day if possible. After three weeks, if the rose is not showing growth, sweat the plant by placing wet sphagnum moss in the center of the crown and then cover the canes with a polyethylene or plastic grocery bag to force new growth. Be careful of excessive heat buildup. Check daily for signs of bud growth, then remove. 

Symptom: Disfigured, discolored or erratic growth. 
Cause: Herbicide damage. 
Remedy: Apply herbicides sparingly (if at all) and only on windless days to prevent drift. Do not apply pre-emergent when warm temperatures could cause volatilization. Wash off any plants that are accidentally sprayed and prune back affected areas. 

Symptom: Sucker growth. This is seen on grafted plants. It is the root stock trying to grow out around the graft. This growth is usually very rapid, producing long canes with no lower leaf buds. Foliage is usually lighter color and thorns are spaced differently then the rest of the plant. 
Cause: Wearing gloves grasp firmly and snap of pull of the sucker from below ground level. 
Remedy: Be sure the growth originates form below the graft. Bottom or basal growth form the graft can be confused with suckers. If in doubt, allow the growth to continue until the difference is visible. You may have to remove suckers throughout the growing season. They are not symptoms of a sick plant but of a healthy, vigorous one.

About the Author

Steve McShane is Founder, Owner and General Manager of McShane’s Nursery & Landscape Supply. Steve is a Soil Science graduate from Cal Poly, San Luis Obispo and has his MBA from Santa Clara University.

Email Steve: steve@mcshanesnursery.com

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