Rose bushes are susceptible to a wide variety of diseases and viral infections. Yellowing of leaves is typically only one factor in the plant's decline. It is essential for gardeners to be able to diagnose what is causing their rose bush leaves to yellow to choose the right management option.
Black spot is caused by a fungus called Diplocarpon rosae. This fungal disease causes yellow rings and black spots to appear on leaves. Eventually, the rose plant may become completely defoliated by the fungal disease especially when temperatures are around 75F and damp. Gardeners should use fungicidal soap and wettable sulphur when treating the rose bush, according to Rose Magazine. Pruning the bush can increase air circulation, which helps control the spread of black spot.
Rose mosaic is a viral disease that causes yellow patterns on green leaves. Gardeners should monitor their rose bushes during times of rapid shoot growth for this infection. Bushes that have been infected decline in health, and the disease can spread to your other rose bushes. It is important for the health of the rest of your rose plants to remove the plant from the area. Burn or throw away the infected rose bush.
Droughts, dry spells and too much watering can cause the yellowing of rose leaves. According to the All American Rose Collection, roses need 1 to 2 inches of water a week. Gardeners can set tuna cans out next to their plants to know how much rain the plant has received each week. If the can is full, the plant doesn't need water. Furthermore, you should water your rose plants at their base to prevent creating a hospitable environment for fungal diseases.
Damage can occur to rose bushes when gardeners hit their root systems while digging up weeds or when mower blades clip the roots or base of the plant. Yellowing of leaves indicates that an inadequate amount of water is reaching the rest of the plant. Prevent root damage by only hand pulling weeds around your rose plants. Spreading a layer of mulch around your plants discourages weeds and creates a shield between the rose bushes and lawnmower.
- Rose Magazine: Blackspot
- North Carolina State University Department of Crop Science, College of Agriculture & Life Sciences; Rose Diseases and Treatment; R.K. Jones and D.M. Benson
- Washington State University Spokane County Extension; Rose Problems: Milo Ball, January 2005
- Garden Grapevine Magazine; Leaf Yellowing on Roses; Nigel Roxburgh
- All-American Rose Collection: Watering Roses