Biology Reference
In-Depth Information
are dark brown or black, irregular, and in addition
there are narrow streaks on petioles, midribs, and
larger veins. Petiole tissue may be softened as
with soft rot. Infection is only through wounds.
Pseudomonas syringae pv. coronafa-
ciens
Halo Blight
on grasses, such as
Poa
spp. and
Calamagrostis
spp.
Pseudomonas syringae pv. delphinii -
Delphinium Black Spot
on delphinium and aco-
nite (monkshood). Irregular tarry black spots on
leaves, flower buds, petioles, and stems may coa-
lesce in late stages to form large black areas. The
bacteria enter through stomata or water pores.
Occasionally this bacterial leaf spot results in
some distortion, but most abnormal growth and
blackening of buds is due to the cyclamen mite,
a much more important problem than black spot.
Control
Remove diseased leaves as noticed; cut
and burn all old stalks at end of season; avoid
overhead watering. In a wet season spraying with
bordeaux mixture may have some value.
Pseudomonas syringae pv. glycinea
Bacterial
Blight
of soybean. Perhaps the most common
and conspicuous disease of soybean, appearing
in fields when plants are half-grown and
remaining active until maturity, with defoliation
during periods of high humidity or heavy dews.
Small, angular, translucent leaf spots, yellow to
light brown, turn dark reddish brown to nearly
black with age. There is often a white exudate
drying to a glistening film on under leaf surfaces.
Black lesions appear on stems and petioles, and
on pods water-soaked spots enlarge to cover
a wide area, darken, and produce an exudate
drying to brownish scales; seeds are often
infected. Seedlings from infected seed have
brown spots on cotyledons and often die. Flam-
beau and Hawkeye varieties are somewhat less
susceptible. Use seed taken from disease-free
pods.
Pseudomonas syringae pv. helianthi
Bacterial
Leaf Spot
of sunflower. Leaves show brown,
necrotic spots, first water-soaked, then dark and
oily.
Pseudomonas syringae pv. hibisci
Bacterial
Leaf Spot
on
Hibiscus
.
Pseudomonas syringae pv. lachrymans
Angular
Leaf Spot
of cucurbits, general on cucumber,
muskmelon, summer squash, occasional on
other cucurbits. Leaves or stems have irregular,
angular, water-soaked spots with bacteria oozing
out in tearlike droplets that dry down to a white
residue. Eventually the spots turn gray, die, and
shrink, leaving holes in foliage. Fruit spots are
small, nearly round, with the tissue turning white,
sometimes cracking. The bacteria overwinter in
diseased plant tissue and in the seed coat. They
are spread from soil to stems and later to fruit in
rainy weather, also transferred from plant to plant
on hands and clothing. Infection is most severe in
plants gone over by pickers early in the morning
before dew has dried off.
Control
Plow under or remove vines immedi-
ately after harvest.
Pseudomonas syringae pv. mori
Bacterial
Blight
of mulberry, general on black and white
mulberry. Numerous water-soaked leaf spots join
to form brown or black areas with surrounding
yellow tissue. Young leaves may be distorted,
with dark sunken spots on midribs and veins.
Dark stripes with translucent borders on young
shoots exude white or yellow ooze from lenticels.
Dead twigs and brown leaves resemble fire
blight; trees are stunted but seldom killed.
Remove and burn blighted branches; do not
plant young mulberry trees near
infected
specimens.
Pseudomonas syringae pv. mors-prunorum -
Bacterial Canker
of stone fruits,
Citrus Blast
,
Lilac
Blight
on many unreleated plants, including
apple, plum, peach, cherry, pear, almond, avo-
cado, citrus fruits, lilacs, flowering stock, rose,
beans, cowpeas, oleander, and leaf spot on peas.
On stone fruits all plant parts are subject to
attack, but most destructive are elongated water-
soaked lesions or gummy cankers on trunks and
branches, usually sour-smelling. Dormant buds
of cherry and apricot are likely to be blighted,
pear blossoms blasted. Small purple spots appear
on leaves of plum and apricot, black lesions on
fruit of cherry and apricot. All varieties of apricot
are very susceptible to the disease. Plums on
Myrobalan rootstock are more resistant, and vari-
eties California, Duarte, and President are toler-
ant. On citrus, and particularly lemons, dark
sunken spots, called black pit, are formed on
