Roses are a favorite flower in America, gracing gardens across the country. When leaves start turning yellow, though, gardeners must diagnose and respond quickly if they want to keep their beauties blooming. Yellowing leaves can be a symptom of several maladies.
Roses like a slightly acidic soil with a pH near 6.7 and require nutrients to grow and produce well. A soil that is too alkaline or deficient in iron may cause general yellowing. Soil with excess phosphorus or potassium may need nitrogen to "green up" leaves.
Crowding can deny leaves the sunlight and air they crave, and they might start to yellow. Over-watering and too much fertilizer can also damage leaves, turning them yellow.
Pre-emergent herbicides used on lawns in the spring can damage roots of nearby plants, such as rose bushes, causing the leaves to turn yellow, and glyphosate spray, a common summer broad-leaf weed killer, may cause yellowing from the point of contact.
Aphids, spider mites, rose scales and leaf hoppers can cause yellow spots and patches on leaves. Use pesticides formulated for the particular insect infecting your roses.
Fungi are transmitted by rain, wind, insects and gardening tools. Black spot is surrounded by a yellow "halo" and rust makes yellow patches with orange or black spores on the underside of the leaf. Prune the affected parts out of your rose bush.
Mosaic virus is a disease transmitted from a parent plant or by insects. It starts with yellow streaks on leaves.