Cause The fungus Erysiphecaprifoliacearumvar.. This fungus is
favored by conditions that produce high humidity but dry leaves. It is a highly
specialized pathogen that forms a close association with the host. Conditions
that favor the host also favor the pathogen. Much of the fungus remains outside
infected plant parts where it grows on the surface but sinks root-like
structures called haustoria into plant cells to obtain nutrients. The white
growth seen is composed of both mycelium and spores of the fungus.
Symptoms The leaves, branch tips, and buds may be covered with a
thin layer or irregular patches of grayish white powdery material. Infected
leaves may turn yellow and drop.
Space plants for good air circulation.
Plant in full sun.
Fungicides will do best when used before
symptoms develop. Few materials have good eradicant activity. Use at 7- to
14-day intervals; using shorter intervals when environmental conditions favor
disease development. Alternate or tank-mix products from different groups that
have different modes of action.
Cygnus 50 WG at 1.6 to 3.2 oz/ 100 gal water plus a
non-organosilicone spreader-sticker. Best used before symptoms develop. Group
11 fungicide.12-hr reentry.
Eagle 20 EW at 6 to 12 fl oz/100 gal water. Group 3 fungicide.24-hr
Myclobutanil 20 EW T&O at 6 to 12 fl oz/100 gal water plus
spreading agent. May observe a PGR effect.Group 3 fungicide.24-hr reentry.
Pageant at 6 to 12 oz/100 gal water. Do not use more than two (2)
consecutive applications before switching to a different fungicide group. Group
7 + 11 fungicide.12-hr reentry.