Biology Reference
In-Depth Information
usually similar to mycelium and interwoven with
it; mycelium brown in rare cases.
Blumeria graminis (see
Erysiphe graminis
).
Powdery Mildew
of cereals and grasses, econom-
ically important on bromegrass, wheat, oats, bar-
ley, and rye; aesthetically important on lawn
grasses, wheatgrass, fescue, and bluegrass.
Brasiliomyces trina (formerly
Erysiphe trina
).
Oak Powdery Mildew
, on tanbark oak and coast
live oak, in California, causing witches' broom
(but
▶
Sphaerotheca lanestris
for the common
live-oak mildew). Perithecia are small, yellow-
brown, with appendages lacking or rudimentary;
asci have two, rarely three, spores.
Erysiphe aggregata
Alder Powdery Mildew
.
Perithecia large, asci with eight spores, rarely
six or seven.
Golovinomyces cichoracearum (formerly
Erysiphe cichoracearum
).
Powdery Mildew
of
cucurbits and many ornamentals, mostly compos-
ites, perhaps best known to gardeners as the
Phlox
Mildew
. Asci are two-spored, perithecia rather
small, haustoria not lobed. There are nearly 300
hosts including: cucumber, squash, pumpkin,
gourds, cantaloupe, watermelon, lettuce, endive,
Jerusalem artichoke, pepper, potato, salsify, Ech-
inacea, Eucalyptus,
Achillea, Anchusa, Artemi-
sia
, aster, begonia,
Boltonia
, calendula,
campanula, chrysanthemum, clematis, coreopsis,
cosmos, dahlia delphinium
Eupatorium
, gaillar-
dia golden-glow, goldenrod,
Helenium
, holly-
hock,
Inula
, mallow
Mertensia
phlox,
rudbeckia,
Salpiglossis
, salvia (sage), sunflower,
stokesia and zinnia.
There are various strains of the fungus, the
form on cucurbits not affecting ornamentals, the
strain of phlox (see
Fig. 3
) is reportedly limited to
that host, the strain on zinnia with a wide range of
host plants. The lettuce strain, perhaps a mutation
of the form on wild lettuce, was not reported on
cultivated lettuce before 1951 and is important
only in California and Arizona. Powdery mildew
was reported on cucurbits in North America in
1890, but did not gain much prominence until
1926, when it suddenly reduced the melon crop
in the Imperial Valley of California by 5000
carloads. By 1939 mildew-resistant Cantaloupe
45 had been developed to meet the situation, but
Fig. 3 Erysiphe cichoracearum
on Phlox
in another decade the fungus had produced
a different strain to which Cantaloupe 45 was
susceptible. Plant breeders can never rest on
their laurels because fungi that are obligate para-
sites seldom stay long outwitted. Other varieties,
Cantaloupes 5, 6, and 7, were bred resistant to
both strains of the fungus.
Powdery mildew is the principal disease of
cucumbers in greenhouse culture, with tiny
white superficial spots on leaves and stems
enlarging and becoming powdery. Young water-
melon fruits in greenhouses have small pimples
or warts under the area covered by mildew
mycelium.
Phlox mildew is only too familiar to gar-
deners. The white coating often appears on vari-
ety Miss Lingard in June, but on other varieties
(in New Jersey) more prominently in July and
August. The mycelium is present on both leaf
surfaces and forms a thick felt on stems. In late
