Treating and preventing rose bush pests and diseases

Roses require regular attention to their needs. Use these guidelines to see causes of disease and infestation in your plants and learn how to properly heal them.

Shoots and flower buds are covered with greenish insects. Severe attacks cause malformation of stems, leaves, and buds.

1. Aphids. Spray plants with a strong stream of water or apply insecticidal soap. Leaves are eaten, sometimes also rolled.
2. Caterpillar. Apply Bacillus thuringiensis kurstaki.
3. Sawfly larvae. Apply neem. Leaves show pale mottling, may yellow and fall prematurely. Small jumping and flying insects on plant.
4. Leafhoppers. Spray plants with a strong stream of water. Apply Beauveria bassiana. Insecticidal soap may provide control. Leaves and flower buds may be severely distorted. Leaves often have tattered or spotted appearance.
5. Plant bugs. Spray with summer oil or insecticidal soap. Flowers are malformed, or buds turn brown and fail to open. Tiny insects scurry among petals.
6. Thrips. Spray plants with a strong stream of water. Apply Beauveria bassiana or spinosad. Leaves are off-colour, often bronzed, with fine silver-white dots. Leaves may be webbed. Two-spotted mites (red spider mites)If problem is severe, spray top and bottom of leaves with insecticidal soap weekly. Knotted galls on roots. Plants are sickly, stunted, off-colour.
7. Root-knot nematodes. Buy plants certified free of nematodes. Do not replant roses in infected soil for four years. Leaves have black rounded spots and may fall prematurely.

1. Black spot (fungus). Spray with fungicidal soap or wettable sulphur. Stems and crowns are attacked, causing dieback and purplish- black to brown cankers.
2. Cankers (fungus). Prune affected stems back to at least 3 cm (1 in) below any discoloured area on stems. Do this after spring growth begins. After each cut, dip knives and pruners in a 1:10 chlorine bleach solution. Spray with lime sulphur. Plants are attacked at soil line, causing large knotty growths.
3. Crown galls (bacteria). Remove and destroy badly affected plants. Take care not to damage stems when working around plants. Difficult to control. Leaves and young shoots have whitish coating. They may be distorted.
4. Powdery mildew (fungus). Spray with baking soda or fungicidal soap. Shoots are twisted or malformed; covered with orange powder. Small yellow spots are visible on undersides of leaves, which may fall prematurely.
5. Rust (primarily on West Coast). Not always easy to control, but spray with wettable sulfur or fungicidal soap at first sign of attack. Cut out and destroy affected shoots. Shoot tips are blackened or purplish. Slightly discoloured patches may occur on young leaves.
6. Frost or cold winds. If this happens regularly, make sure final pruning is delayed until spring so that young shoots are produced later. Leaves yellow and fall early. Flowers are few and short-lived. General growth is thin and poor.
7. Starvation, drought, or combination of both. Make sure that soil does not dry out. Mulch annually with well-decayed manure or garden compost, plus rose fertilizer.