Biology Reference
In-Depth Information
infects many other trees, shrubs, and vines,
including azalea, beech, bittersweet, birch,
catalpa, dogwood, elder, elm, euonymus,
forestiera, hazelnut, magnolia, mountain-holly,
plane, New Jersey tea, privet, trumpetvine, and
viburnum. According to some taxonomists the
proper name of this species is
Microsphaera
penicillata
, but
M. alni
is more familiar and still
widely used. Mildew is prevalent on lilac in late
summer and fall, sometimes in dry seasons,
almost completely covering foliage with a thick
white coating; but, because it comes so late in the
season, it is not very injurious. It is also common
on deciduous azaleas in late summer, forming
a very thin grayish white coating with numerous
prominent dark perithecia. This species is more
prevalent than the legume mildew on sweet peas,
but it is chiefly a greenhouse problem in spring,
when temperatures and humidity are less uni-
form. The foliage may be malformed, dropping
prematurely or drying out and shriveling.
Among tree hosts oaks are probably most sus-
ceptible, but it would seldom pay to attempt con-
trol measures except in nursery rows. On pecans
the white coating starts forming on leaves and
nuts in July with occasional defoliation, shuck
splitting, and shriveled kernels. Most commercial
pecan varieties are mildew-resistant.
Blueberry Mildew is caused by a special strain
of lilac mildew, reported as
Microsphaera
vaccinii
, and
M. penicillata
var.
vaccinii
. Varie-
ties Pioneer, Cabot, and Wareham are said to be
particularly susceptible; Concord, Jersey, and
Rubel are intermediate; and Stanley, Rancocas,
Harding, and Katherine, highly resistant. On
some blueberries the mycelium is conspicuous
on upper leaf surfaces, on others barely visible
on underside. Midsummer defoliation weakens
the bushes. Cranberries, farkleberries, trailing
arbutus and lyonia are possible hosts to this
strain.
Control
Bordeaux mixture is recommended for
pecans - two applications, June and July. Dust
blueberries with sulfur. Use sulfur on lilacs and
other ornamentals.
Microsphaera diffusa General on snowberry,
widespread on wolfberry, coralberry, occasional
on black locust,
soybean. Appendages are two to four times the
diameter of the perithecia, with ultimate branches
long, forming a narrow fork.
Microsphaera
euphorbiae On
lima
bean,
euphorbia, roselle.
Microsphaera grossulariae
European Pow-
dery Mildew
, occasional on currant, gooseberry.
There is a light weft of mycelium mainly on
upper surface of leaves. For the more important
American mildew
Sphaerotheca mors-uvae
.
Microsphaera penicillata
Powdery Mildew
on
Leucothoe¨ axillaris
.
Microsphaera pulchra
Powdery Mildew
on
flowering dogwood.
▶
Oidium
This term is used for mildews known solely from
the conidial stage. In some cases the type of
conidial fructification may suggest correct gen-
era, but until perithecia are found,
Oidium
is
preferred.
Oidium araliacearum
Powdery Mildew
on
English Ivy.
Oidium begoniae
Begonia Mildew
, especially
important on tuberous begonias on the West
Coast, though it may also occur on fibrous-rooted
begonias.
Oidium dianthi
Carnation Powdery Mildew
.
Oidium euonymus japonici
Euonymus Mil-
dew
, general throughout the South and on the
Pacific Coast on
Euonymus japonicus
. The myce-
lium forms a thick felt on the leaf surface, causing
some yellowing and defoliation (see
Fig. 4
).
I have seen this disease rampant in foggy coast
towns like Beaufort, South Carolina, or Mobile,
Alabama, and equally severe in semiarid El Paso,
Texas. The washing effect of a water spray
applied with pressure, either by adjusting the
hose nozzle or putting the thumb over a portion
of the orifice, is a deterrent to this mildew. Sulfur
dust can be used, probably Karathane.
Oidium obductum On oriental plane.
Oidium pyrinum On crabapple.
Oidium tingitaninum
Citrus Mildew
, common
in Java, Ceylon, India, but in this country causing
only limited injury to tangerine
lima bean, kidney bean and
trees
in
