See:
Hebe (Veronica spp.) - Downy Mildew
Cause Peronospora grisea, a fungus-like organism. Moist or very humid conditions favor sporulation and disease development. Spores are dispersed by wind and splashing water. Spores germinate and infect when free water is present on the leaves.
Symptoms Chlorosis, stunting of shoots, and distortion of the younger growth. Distorted leaves may have sporulation on the underside that looks fuzzy gray. Upper leaf surfaces may show purple sections.
Cultural control
- Space plants for good air circulation.
- Water such that plants are not wet for extended periods of time.
- Remove and destroy infected plants. Don't purchase diseased plants.
Chemical control Use before symptoms develop. Alternate or tank-mix products from different groups that have different modes of action. Although not many fungicides are registered for this crop, there may be several others that are effective and legal to use. Try on a few plants first to test for phytotoxicity before wide scale use.
- Heritage at 1 to 4 oz/100 gal water plus a non-silicone-based wetter sticker. Group 11 fungicide. 4-hr reentry.
- Phyton 27 at 1 to 2 fl oz/10 gal water. Group M1 fungicide. 48-hr reentry.
Reference Gleason, M.L., Daughtrey, M.L., Chase, A.R., Moorman, G.W., and Mueller, D.S. 2009. Diseases of Herbaceous Perennials. APS Press, St. Paul, MN.