Shrub Diseases

Black Spot (Diplocarpon rosae) on Roses

Black Spot shrub rose disease

The characteristic black leaf spots are circular with feathery borders surrounding the spots. Black Spot disease is caused by a fungal pathogen. Once the disease has progressed to the point where black spots are visible it means that the plant tissue has been permanently damaged. Because this disease is so difficult to control, there are no repeat service calls after the initial treatment.

Leaf Spot (Entomosporium mespili) on Hawthornes

Leaf Spot shrub disease

When a hawthorne is affected by the leaf spot, the leaves will turn a yellowish color and drop off. This disease can initially be identified by the presence of small, angular purple dots. When hawthornes are affected by the leaf spot, it can be especially damaging to the plant. Control measures include removing infected leaves that have fallen to the ground and applying fungicide. Both are necessary for control.

Leaf Spot (Cercospora) on Ligustrums

Leaf Spot shrub disease

Low levels of leaf spot usually cause little more than cosmetic damage. Severe leaf spot fungi attack leaves and can cause premature leaf drop. The disease spots are usually light to dark brown with a yellow border. Control measures include applying a fungicide.

Leaf Spot (Entomosporium maculatum) on Red Tip Photinias

Leaf Spot shrub disease

Low levels of leaf spot on red tip photinias usually cause little more than cosmetic damage but maintain a source of spores for future infections. Severe infections often result in early and heavy leaf drop. Heavy leaf drop severely reduces the landscape value of red tip and can cause plant death. Mild temperature and prolonged leaf wetness are the requirements for infection. Removing infected leaves that have fallen to the ground and a contact fungicide is used for control.

Powdery Mildew on Shrubs

Powdery Mildew shrub disease

Powdery mildew is a fungal disease attacking leaves, shoots, buds and flowers. It produces numerous spores which, when seen under a microscope, resemble chains of beads. The result is a powder-like dusting that grows in thin layers on the plant tissue surfaces. Powdery mildew is most evident on young, actively growing plant tissues. It can cover new growth entirely in late spring and into early summer and cause severe damage to those plant tissues, causing leaves to become misshapen and even delaying the first summer bloom until the disease abates.


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