What is Wrong with my Roses?
A rose problem is almost always a reflection of the plant’s environment. Bad drainage, too little water, poor soil preparation, insects, and disease – all are environmental conditions that can either be remedied or prevented from the start.
This information, prepared by Jackson & Perkins, will help you diagnose and treat problems. Our garden center staff will be helpful in identifying a pest or disease or in recommending a treatment.
The first line of defense against any rose problem is a strong, healthy plant. A little advance preparation such as the addition of peat or well-composed organic material to the soil before planting will provide a blooming environment.
Symptom: Masses of bugs on the buds and leaves.
Cause: Aphids – red, green or black soft bugs, about 1/8” long, found mostly on new growth. They appear early and can stay around or come back all summer.
Remedy: Most insecticide sprays, including insecticide soap, are effective. Aerosol insecticides labeled for plant pests will also work – spray up-wind and allow the mist to drift through the plant. Later, wash off the insects with hose 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 definitely spread by wind.
Remedy: Apply insecticides containing acephate when the buds are pea-sized, then again at two-week intervals. Follow instructions on the label for mixing and spray intervals.
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: Sprays Insecticide soap, miticides, and high-pressure hose water. All treatments must be applied from the bottom up in order to contact the insect, which is always on the leaf underside.
Symptom: Leaves have been eaten leaving either skeleton structure or midribs. 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 Diazinon are somewhat effective. Apply Bp (Bacillus papillae) or ‘milky spore’ when the grubs are first detected in spring or late summer. Neem oil, a new natural insecticide, or its derivative Azadirachtin, has show some limited control. Practical, yet effective, is to spread cloth or plastic on the ground and shake the beetles off the plants. Traps can also be effective if placed away from your roses.
Symptom: Leaves stuck together, unopened buds with holes bored into them.
Cause: Omnivorous leaf roller – This is a moth larvae that makes a cocoon-like structure with leaves.
Remedy: B.T. (Bacillus thuringiensis) or Orthene used as previously explained for thrips.
Symptom: Holes in pruned cane ends. Circular pieces cut from leaf margins.
Cause: Leaf cutter bee – They are the circular leaf pieces for egg partitions inside the burrowed cane.
Remedy: Controlled by applying white glue to the cane ends.
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 Diazinon 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: Slow starting roses.
Possible Cause: Dry canes, dry roots.
Remedy: Water the roses heavily during 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 clear polyethylene bag or burlap to force new growth. Be careful of excessive heat buildup. Check daily for signs of bud growth, then remove.
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 than the rest of the plant.
Remedy: Wearing gloves grasp firmly and snap or pull off from below ground level. Be sure the growth originates from below the graft. Bottom or basal growth from 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.
Symptom: Leaves fold at mid-rib, or are distorted. White powdery material appears on the forming buds and leaf tops or undersides.
Cause: Powdery Mildew – Fostered by cool nights, warm days and high humidity.
Remedy: Dust with sulphur, or spray with baking soda and soap.
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-sulphur spray. Remove dropped leaves and other debris. Spray with Neem oil, Garden Defense, or a sulphur-based fungicide. The fungus spores are on leaf undersides so spray up from underneath. Spray in the early morning when weather is calm and cool. When watering, keep foliage dry or water in the morning so foliage dries by midday.
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 Garden Defense. Clean up all twigs on the plant and leaves and debris below to prevent fungus from spreading. Maintain good air circulation.
Symptom: Dark irregular splotches on the leaves, dropping of healthy leaves, yellowed leaf sections.
Cause: Downy Mildew – A systemic fungus disease. It is present in the soil and will begin to cause problems when night temperatures reach 55-65 degrees, with still air measuring 85% humidity.
Remedy: Cut back the defoliated plant. Clean up debris, dust with sulfur and spray with Garden Defense. (Be careful to spray Garden Defense only in the morning so it will dry before hot mid-day temperatures occur.)
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 contaminated pruning tool.
Remedy: Prune away the 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 seasons before replanting.