Cause Powdery mildew has been observed on Geum spp. in all states. Podosphaera aphanis, P. macularis and Erysiphe polygoni have been reported from Washington and Idaho. Disease appears to be worse in shaded areas of gardens.
Symptoms White powdery patches occur on both sides of the leaves and on stems. Distribution is scattered on leaves and plants. Whole leaves may be covered later in the development of the disease.
Cultural control
- Space or thin plants for good air circulation.
Chemical control There are no fungicides specifically registered for this crop. Many fungicides are legal to use if not phytotoxic and may have activity against this disease:
Reference Dugan, F.M., and Glawe, D.A., 2007. Powdery mildews on weeds in the Pacific Northwest: a miscellany of new records. North American Fungi, 2, pp.1-7.