Downy mildew causes pale spots on the upper sides of leaves. Corresponding regions on the undersides of the leaves are covered with grayish mildew. No chemical control is listed.
Leaf spot causes numerous small circular spots which vary in color from violet to brown. The spots are found on the upper leaf surface. On the undersides the spots are yellowish brown. As the spots run together the leaves look scorched, ragged and shotholed. The last stage of the disease is defoliation. Destroy all fallen and spotted leaves. The disease is caused by Septoria veronicae and no chemical control is listed.
Powdery mildew causes a white powdery growth on the leaves. The disease can be controlled with benomyl or sulfur.