Biology Reference
In-Depth Information
Fig. 1
Powdery Mildew:
mycelium and conidia
formed on surface of a leaf
and two types of the
haustoria in host cells
Fig. 2
Powdery Mildews.
Perithecia (cleistothecia) of
the six genera:
Erysiphe
,
simple appendages and
several asci;
Sphaerotheca
,
same with one ascus;
Mycrosphaera
,
dichotomously branched
appendages and several
asci;
Podosphaera
, same
with one ascus;
Phyllactinia
, appendages
bulbous at base;
Uncinula
,
appendages coiled at tip
Powdery mildews are obligate parasites, hav-
ing no saprophytic growth periods in dead
plant parts, although the perithecia carry the fun-
gus through the winter on either living or dead
tissue. Mycelium sometimes winters in buds.
Symptoms of mildew are dwarfing and stunting,
often with a slight reddening and curling of
leaves before the white mycelium is noticeable.
There may be deformation of flower buds. Such
symptoms are due to the withdrawal of plant
foods by the fungus and to excessive respiration.
Sulfur dust and lime sulfur sprays have long
been considered specific remedies for powdery
mildews; some copper sprays are effective.
Many of the newer organics are ineffective.
However, inorganics, in a formulated form,
i.e. potassium biocarbonate are very effective
and safe.
Erysiphe
Cleistothecia globose, or globose-depressed,
sometimes concave; asci several, two-to eight-
spored; appendages floccose (cottony), simple
or
irregularly branched; sometimes obsolete,
