Troubleshooting Common Rose Problems: Diseases and Pests

Black Spot

Problem: Small, fringed, black-to-brown spots on leaves appear first, then leaves yellow and drop. Symptoms start at the bottom and move up. Common in warm, humid weather.

Solution: Remove and discard infected leaves. To reduce infection, try a baking soda-oil spray (2 teaspoons baking soda + 2 teaspoons summer oil in 1 gallon water). Apply often to protect new growth.

Powdery Mildew

Problem: Patches of white fungal filaments and spores disfigure leaves, buds, and stems. Thrives in humid air but needs dry foliage to establish.

Solution: Overhead watering in early morning may wash off spores. Baking soda-oil sprays (see black spot) can help. For severe cases, spray with fungicide like triforine or benomyl.

Rust

Problem: Small rust-colored spots on leaf undersides; leaf tops show yellow mottling; advanced cases cause yellowing and drop. Warm days, cool nights, and moisture encourage this spore-spread fungus.

Solution: Keep fallen leaves picked up; in winter, remove any rust-infected leaves remaining on the plant. During growing season, spray foliage with wettable sulfur or fungicide like triforine.

Aphids

Problem: Small green, red, pink, or black oval insects cluster on new leaves, undersides, and buds, distorting them by sucking plant juices.

Solution: For light infestations, do nothing; beneficial insects like ladybugs will feed on them. For heavier infestations, dislodge with a strong water spray or spray with insecticidal soap.

Spider Mites

Problem: Barely visible spiderlike insects on leaf undersides, often weaving delicate webs. They suck juices, turning leaves stippled yellow.

Solution: Spray leaves with water in early morning. For heavy infestations, spray with insecticidal soap or summer oil.