Biology Reference
In-Depth Information
fruit rind, but there is no decay. The blast form of
the disease is most often on oranges and
grapefruit - water-soaked areas in leaves, which
may drop or hang on, twigs blackened and shriv-
eled. The disease is most serious in seasons with
cold, driving rainstorms.
On lilac, brown water-soaked spots on leaves
and internodes on young shoots blacken and rap-
idly enlarge. Young leaves are killed; older
leaves have large portions of the blade affected.
Infection starts in early spring in rainy weather.
The bacteria are primarily in the parenchyma,
spreading through intercellular spaces, blacken-
ing and killing cells, forming cavities. The vas-
cular system may also be affected, followed by
wilting of upper leaves.
Control
Prune out infected twigs and branches.
In California spray fruits in fall with bordeaux
mixture, at the time first leaves are dropping.
Grow bushy, compact citrus trees less liable to
wind injury; use windbreaks for orchards.
Pseudomonas syringae pv. papulans
Blister
Spot
of apple. Small, dark brown blisters on
fruit and rough bark cankers on limbs start at
lenticels. Bark may have rough scaly patches
from a few inches to a yard long, bordered with
a pimpled edge, and with outer bark sloughing off
in spring.
Pseudomonas syringae pv. phaseolicola
Bean
Halo Blight
, halo spot on common, lima, and
scarlet runner beans. The symptoms are those of
other bean blights except that there are wide
green or yellowish green halos around water-
soaked leaf spots, such spots later turning brown
and dry. Leaves wilt and turn brown; young pods
wither and produce no seed; sometimes plants are
dwarfed with top leaves crinkled and mottled. In
hot weather, spots are often angular, reddish
brown, and without halo. Stem streaks are red-
dish, with gray ooze; pod spots are red to brown
with silver crusts; seeds are small, wrinkled, with
cream-colored spots. All snap beans are suscep-
tible; many dry beans - Pinto, Great Northern,
Red Mexican, Michelite - are rather resistant.
Control
Use seed from blight-free areas. Blight
is rare in California, occasional in Idaho. Plan
a 3-year rotation. Do not pick beans when foliage
is wet.
Pseudomonas syringae pv. pisi
Bacterial Blight
of pea, general on field and garden peas, espe-
cially in East and South, and causing a leaf spot of
sweet peas. Dark green water-soaked dots on
leaves enlarge and dry to russet brown; stems
have dark green to brown streaks. Flowers are
killed or young pods shriveled, with seed covered
with bacterial slime. Bacteria enter through sto-
mata or wounds, and if they reach the vascular
system, either leaflets or whole plants wilt. Vines
infected when young usually die. Alaska and
Telephone varieties are particularly susceptible.
Control
Avoid wounding vines during cultiva-
tion. Sow peas in early spring in well-drained
soil. Use disease free seed and plan a 4-year
rotation.
Pseudomonas
syringae
pv.
porri
Bacterial
Blight
of shallot.
Pseudomonas syringae pv. primulae
Bacterial
Leaf Spot
of primrose in ornamental and com-
mercial plantings in California. Infection is con-
fined to older leaves - irregularly circular brown
lesions surrounded by conspicuous yellow halos.
Spots may coalesce to kill all or part of leaf.
Spraying with bordeaux mixture has prevented
infection.
Pseudomonas syringae pv. savastanoi
Olive
Knot
,
Bacterial Knot
of olive. Irregular, spongy,
more or less hard, knotty galls on roots, trunk,
branches, leaf, or fruit pedicels start as small
swellings and increase to several inches with
irregular fissures. Terminal shoots are dwarfed
or killed; whole trees may die. Bacteria enter
through wounds, often leaf scars or frost cracks.
Variety Manzanilla is most susceptible of the
olives commonly grown in California. Another
form of this species causes similar galls on ash.
Control
Cut out galls carefully, disinfesting
tools; paint larger cuts with bordeaux paste and
spray trees with bordeaux mixture in early
November, repeating in December and March if
infection has been abundant. Do not plant
infected nursery trees or bring equipment from
an infected orchard into a healthy one.
Pseudomonas syringae pv. syringae
Brown
Spot, Foliar
on wild rice (
Zizania
); leaf spot and
stem collapse on urd bean; leaf spot and stem
canker on Ginkgo.
