Biology Reference
In-Depth Information
Peronospora rumicis
Rhubard Downy Mil-
dew
. A European disease reported from Califor-
nia on garden rhubarb. Fungus winters
Control
Use seed grown in the West where mil-
dew is not present; plan a 2 to 3-year rotation.
Copper dusts are satisfactory.
in
rootstalks and grows up into new leaves.
Peronospora
Peronospora
farinosa
).
Beet Downy Mildew
, on beet, sugar
beet, and swiss chard.
Peronospora sorghi (see
schactii (see
▶
Plasmopara
Oomycetes, Peronosporales
Peronosclerospora
sorghi
). Downy mildew, on sweet corn.
Peronospora sparsa
Rose Downy Mildew
,
chiefly on roses under glass, rarely outdoors.
Young foliage is spotted, leaves drop; flowers
are delayed or unmarketable. Abundant spores
are produced on undersurface of leaves. To con-
trol, keep humidity below 85 % and daytime
temperature relatively high.
Peronospora
▶
Sporangiophores with monopodial branches, with
obtuse tips, arising more or less at right angles;
haustoria unbranched and knoblike; sporangia
(conidia) small, hyaline, papillate, germinating
sometimes by germ tubes but usually by swarm
spores; oospores yellowish brown, outer wall
wrinkled, sometimes reticulate, oogonial wall per-
sistent but not fused with oospore wall (see
Fig. 1
).
Plasmopara
statices
Downy Mildew
on
statice.
Peronospora tabacina
Blue Mold
of tobacco,
Downy Mildew
; also on eggplant, pepper, and
tomato. This is a seedling disease that can be
controlled by sprays on eggplant and pepper; it
is unimportant on tomato.
Peronospora trifoliorum
Downy Mildew
of
lupine, and alfalfa.
acalyphae
Acalypha
Downy
Mildew
.
Plasmopara geranii on geranium P. gonolobi
on gonolobus.
Plasmopara halstedii
Downy Mildew
of bur-
marigold, centaurea, erigeron, eupatorium,
gnaphalium, goldenrod, hymenopappus, Jerusa-
lem artichoke, ratibida, rudbeckia, senecio,
silphium, verbesina, and vernonia. Zoospores
germinate in soil moisture and invade seedlings
via root hairs; myceliummoving up into stem and
leaves causes early wilting and death. Older
plants may not die but exhibit a light yellow
mottling. Sporangiophores project through sto-
mata on underside of leaves. The fungus winters
in seed and as oospores in soil.
Plasmopara crustosa (formerly
Plasmopara
nivea
).
Downy Mildew
of carrot, parsley, pars-
nip, and chervil. Yellow spots on upper surface of
foliage and white mycelial wefts on under surface
turn dark brown with age. The disease is rela-
tively infrequent, important when plants are so
crowded they cannot dry off quickly after rain or
heavy dew. Control by spacing rows properly.
Plasmopara nivea (see
Phytophthora
Blights
.
Phytophthora phaseoli
Downy Mildew
of
lima bean, most important in Middle and North
Atlantic states, in periods of cool nights, heavy
dews, and fairly warm days. Some seasons it
takes 50 to 90 % of the crop; in other years it
is of little consequence. The white downy mold
is conspicuous on the pod, either in patches or
covering it completely. The fungus grows
through the pod wall into the bean, then the pod
dries, turns black. On leaves the white mycelial
weft appears sparingly, but veins are often
twisted, purplish, or otherwise distorted. Young
shoots and flowers are also attacked, bees
and other insects carrying spores from diseased
to healthy blossoms. The fungus fruits abun-
dantly on pods, stems, and leaves; spores are
splashed by rain.
▶
Plasmopara crustosa
).
Downy Mildew
of carrot, parsley, parsnip, and
chervil.
Plasmopara pygmaea, on anemone, and
hepatica. Fine white mildew covers underside of
leaves; plants are distorted, stems aborted.
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